Measurement of the semileptonic \( \mathrm{t}\overline{\mathrm{t}} \) + γ production cross section in pp collisions at \( \sqrt{s}=8 \) TeV

Journal of High Energy Physics, Oct 2017

A measurement of the cross section for top quark-antiquark (\( \mathrm{t}\overline{\mathrm{t}} \)) pairs produced in association with a photon in proton-proton collisions at \( \sqrt{s}=8 \) TeV is presented. The analysis uses data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.7 fb1. The signal is defined as the production of a \( \mathrm{t}\overline{\mathrm{t}} \) pair in association with a photon having a transverse energy larger than 25 GeV and an absolute pseudorapidity smaller than 1.44. The measurement is performed in the fiducial phase space corresponding to the semileptonic decay chain of the \( \mathrm{t}\overline{\mathrm{t}} \) pair, and the cross section is measured relative to the inclusive \( \mathrm{t}\overline{\mathrm{t}} \) pair production cross section. The fiducial cross section for associated \( \mathrm{t}\overline{\mathrm{t}} \) pair and photon production is found to be 127 ±27 (stat+syst) fb per semileptonic final state. The measured value is in agreement with the theoretical prediction.

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Measurement of the semileptonic \( \mathrm{t}\overline{\mathrm{t}} \) + γ production cross section in pp collisions at \( \sqrt{s}=8 \) TeV

Received: June 8 TeV A measurement of the cross section for top quark-antiquark (tt) pairs proThe analysis uses data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.7 fb1. The signal is de ned as the production of a tt pair in association with a photon having a transverse energy larger than 25 GeV and an absolute pseudorapidity smaller than 1.44. The measurement is performed in the ducial phase space corresponding to the semileptonic decay chain of the tt pair, and the cross section is measured relative to the inclusive tt pair production cross section. The ducial cross section for associated tt pair and photon production is found to be 127 tonic nal state. The measured value is in agreement with the theoretical prediction. Hadron-Hadron scattering (experiments); Top physics - The CMS collaboration 1 Introduction 2 The CMS detector 3 Signal and background modeling 4 Event reconstruction and selection 5 Analysis strategy 6 Multijet and Z+jets background estimation 7 Estimate of top quark pair production 7.1 7.2 Measurement of the tt yield Measurement of the top quark purity 8 Photon purity measurement 9 The tt + yield measurement 10 Calculation of the cross section ratio 11 Sources of systematic uncertainty 12 Results 13 Summary The CMS collaboration 1 Introduction As the heaviest elementary particle in the standard model (SM), the top quark has the potential to provide insights into physics beyond the SM (BSM). Many BSM models introduce changes within the top quark sector [ 1, 2 ], which can be constrained by precise measurements of the cross sections and properties of top quark production channels [3]. By measuring the associated production cross section of a top quark-antiquark pair and a photon (tt+ ), the coupling of the top quark and the photon is probed [ 4, 5 ]. Any deviation of the measured cross section value from the SM prediction would be an indication of BSM physics, such as the production of an exotic quark with electric charge of 4/3, or a top quark with an anomalous electric dipole moment [6, 7]. { 1 { g t ¯ t γ W+ W− b q top quarks (left), and through quark-antiquark annihilation with a photon emitted from one of the decays leptonically, resulting in an electron or muon and a corresponding neutrino , and the other W boson decays hadronically. Examples of two Feynman diagrams for the tt+ process in the semileptonic nal states are shown in gure 1. In the signal de nition we include possible contributions from W ! , where the lepton decays further into an electron or a muon. The presence of a charged lepton from the W boson decay signi cantly improves the power to reject dominant backgrounds from multijet processes and allows for e cient triggering of signal events using single-lepton triggers. Measurements of the production cross section of tt+ have been performed by the CDF Collaboration at the Tevatron using pp collisions at p Collaboration at the LHC using pp collisions at p s = 7 TeV [9] and p results are in agreement with the SM predictions within uncertainties [11]. s = 1:96 TeV [8], and by the ATLAS s = 8 TeV [10]. These In this paper, the measurement of the tt+ production cross section in pp collisions at p s = 8 TeV is presented. The analysis is based on a data sample corresponding to an integrated luminosity of 19:7 fb 1, recorded with the CMS detector in 2012. The measurement of the tt+ production cross section in the semileptonic decay channel is performed relative to the tt production cross section. The tt+ cross section is measured in a ducial kinematic region de ned by the presence of exactly one charged lepton and corresponding neutrino, at least three jets, and a photon within the selection requirements. 2 The CMS detector The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic eld of 3.8 T. Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter, each composed of a barrel and two endcap sections. Forward calorimeters extend the pseudorapidity coverage provided by the barrel and endcap detectors. Muons are detected in gas-ionization chambers embedded in the { 2 { steel ux-return yoke outside the solenoid. In the barrel section of the ECAL, an energy resolution of about 1% is achieved for unconverted or late-converting photons in the tens of GeV energy range, relevant to this analysis. The remaining barrel photons have a resolution of about 1.3% up to j j = 1, rising to about 2.5% at j j = 1:4. In the endcaps, the resolution of unconverted or late-converting photons is about 2.5%, while the remaining endcap photons have a resolution between 3 and 4% [12]. A more detailed description of the CMS detector, together with a de nition of the coordinate system used and the relevant kinematic variables, can be found in ref. [13]. 3 Signal and background modeling The signal process produces events in which a pair of top quarks is produced in association with a photon. This process includes photons radiated from the top quarks as well as from initial state partons or the decay products of the top quarks. The simulation of the tt+ signal process is performed in the region with photons having transverse momentum (pT) of at least 13 GeV and j j < 3:0, as well as having a separation from all other generated particles of at least R > 0:3, where R = )2 + ( )2, and and are the p ( di erences in the azimuthal angle (in radians) and pseudorapidity, respectively, between the generated particles and the photon. For the purpose of this analysis, nonprompt photons originating from jets are not included in the de nition of the tt+ signal process. The tt+ signal process is simulated at leading order (LO) using the MadGraph v5.1.3.30 generator [14]. The dominant backgrounds, tt, V+jets, and V+ (where V = W, Z), are also simulated using the MadGraph generator. Single top quark production is simulated at next-to-leading order (NLO) using the powheg v1.0 r1380 event generator [15{18]. In order to avoid any overlap between the simulation of the tt+ signal and the inclusive tt process, events that fall under the tt+ signal de nition are removed from tt simulation. Overlap between V+ and V+jets simulation is also taken into account by removing events from V+jets samples, which are accounted for in the V+ simulation. Approximately 1% of events from tt simulation and approximately 3% of V+jets events are removed through this procedure. The parton showering and hadronization for all simulated samples are handled by pythia v6.426 [19], with the decays of leptons modeled with tauola v27.121.5 [20]. The CTEQ6L1 and CTEQ6M [21] parton distribution functions (PDFs) are used for samples simulated at LO and NLO, respectively. A top quark mass mt = 172:5 GeV is used in the simulation. The response of the full CMS detector is simulated with Geant4 v9.4 [22, 23], followed by a detailed trigger simulation and event reconstruction. The pythia event generator is used to simulate the presence of additional pp interactions in the same and nearby bunch crossings (\pileup"). Simulated events are reweighted to correct for di erences between the number of pileup interactions observed from data and the number produced in the simulation. A cross section of 244:9 6:4 (lumi) pb is used to normalize the tt background [24]. The next-to-next-to-leading-order (NNLO) SM prediction is calculated with fewz v3.1 [25, 26] for the V+jets backgrounds. The W+ and Z+ simulations are { 3 { HJEP10(27)6 normalized to their NLO predictions, calculated with mcfm v6.6 [27]. Values of 553.9 pb for the leptonic decay of the W+gamma process and 159.1 pb for the leptonic decay of the Z+gamma process are used. The single top quark samples are normalized to their approximate NNLO predictions [28, 29]. 4 Event reconstruction and selection The nal state of the signal process in the semileptonic decay channel consists of a high-pT charged lepton, momentum imbalance due to the presence of a neutrino, jets originating from both the b quarks and from the decay of a W boson, and an energetic photon. Events with either a high-pT electron or muon are initially selected through a single-lepton trigger. Events in the e+jets nal state must pass a trigger requiring an electron with pT > 27 GeV within j j < 2:5 and a relative isolation of less than 0.2, where the relative isolation is de ned as the sum of the pT of all particles, excluding the lepton, within a cone around the lepton of R = 0:3, divided by the pT of the lepton. The +jets nal state requires a single-muon trigger selecting a muon with pT > 24 GeV within j j < 2:1 and relative isolation less than 0.3 within R = 0:4. Events are additionally required to have a well reconstructed primary vertex [30], chosen as the one having the largest sum p2T of the tracks associated with it. The particle- ow (PF) algorithm is used to reconstruct individual particles in the event [31]. The PF objects include electrons, muons, charged and neutral hadrons, photons, and an imbalance of the transverse momentum. The following describes the selection of reconstructed objects that are used in the analysis. Electrons are reconstructed from energy deposits in the ECAL matched to a track from the tracker [32]. Electrons are required to have pT > 35 GeV and j j < 2:5. excluding the transition region between the barrel and endcap of the ECAL, 1:44 < j j < 1:57. Electrons from the decay of the top quark are expected to be isolated from other activity in the detector and thus have a requirement that the relative isolation must be less than 0.1. Selected electrons are required to be originating from the primary vertex, and are rejected if identi ed as likely having originated from a converted photon. Additionally, a multivariate-based identi cation is applied to reduce the contribution from nonprompt or misidenti ed electrons. Electrons that fail the above criteria, but pass looser identi cation requirements (pT > 20 GeV, j j < 2:5, and a relative isolation less than 0.2 within a cone of size R = 0:3) are considered to be \loose" electrons. The presence of loose electrons can then be used to reject events from the dilepton Muons are reconstructed based on measurements from both the tracker and muon systems. Selected muons are required to have pT > 26 GeV and j j < 2:1. A requirement on relative isolation less than 0.2 within a cone of R = 0:4 is applied. Loose muons are de ned as failing the tight requirements but passing a selection in which the pT threshold is lowered to 10 GeV and j j < 2:5, with the same requirement on the relative isolation as the tight selection. Jets are reconstructed from PF candidates clustered using the anti-kT algorithm with a distance parameter of 0.5 [33, 34]. Jets must have pT > 30 GeV and j j < 2:4. To remove { 4 { the contribution to the jet energy from pileup interaction, charged hadrons candidates associated with other vertices are not included in the clustering, and an o set correction to the energy is applied for the contribution of neutral hadrons that would fall within the jet area. Additionally, corrections for the jet energy scale and resolution are applied in simulation, to account for imperfect measurements of the energy of the jet in the detector [35]. Jets are identi ed as originating from the hadronization of b quarks (b tagged) using the combined secondary vertex algorithm, which combines secondary vertex and trackbased lifetime information to provide a discriminant between jets originating from the fragmentation of b quarks and light quarks or gluons. The b tagging algorithm has an e ciency of approximately 70%, while having a probability of incorrectly b tagging a light jet of only 1.4% [36, 37]. Photons are reconstructed as energy deposits in the ECAL that are not matched to track seeds in the pixel detector [12]. The photon is required to have pT > 25 GeV and j j < 1:44 (ECAL barrel). A selection based on the shape of the shower caused by the photon in the ECAL is applied using the variable, which measures the lateral spread of energy in the space [12]. Selected photons are required to have < 0:012. This is used to distinguish genuine photons from hadronic activity that can be reconstructed as a photon, as the latter will tend to produce a wider energy spread in , leading to a larger value of . As photons can convert into a pair of electrons before reaching the calorimeter, photon showers along can be larger compared to that of an electron. Thus, the isolation is de ned di erently for photons than it was for leptons, in order to account for a possible energy leakage along . A characteristic photon energy deposition pro le, or \footprint", is used to restrict the area used to calculate isolation of the photon candidate. The charged-hadron isolation variable for photons is de ned as the sum of the pT of all charged hadrons spatially separated from the photon candidate by R = 0:3, but not falling within the photon footprint. The charged-hadron isolation is required not to exceed 5 GeV for selected photons, to help distinguish prompt photons from nonprompt photons produced from hadronic activity. The missing transverse momentum (pTmiss) is de ned as the magnitude of the vector sum of the momenta of all reconstructed PF candidates in the event, projected on the plane perpendicular to the beams. The nal event selection is divided in two steps: a preselection designed to select events with the same topology as top quark pairs (referred to as the \top quark selection"), and a \photon selection". The top quark selection requires: exactly one lepton passing the selection requirements (either an electron or muon); no other lepton candidates passing loose selection criteria; at least 3 jets, with at least one of these jets passing the b tagging requirement; and T pmiss > 20 GeV. The photon selection requires that events pass the top quark selection and additionally have at least one photon passing the identi cation and isolation requirements described above. { 5 { Analysis strategy After the photon selection is applied, over half of the events in simulation originate from background processes, and not tt+ production. The two largest backgrounds are from tt events that have a nonprompt photon coming from jets in the event and from V+ events. There is not a single variable that can su ciently discriminate both of these backgrounds from the tt+ signal. The V+ background can be di erentiated from tt+ events by attempting to reconstruct a top quark in the event. However, tt events are very similar to the signal in this respect. Alternatively, the nonprompt photon from the tt background will tend to be less isolated than the photons from the tt+ signal, but the photon isolation variable does not have discrimination power to distinguish the V+ background from tt+ events. In order to be able to distinguish both tt and V+ background events, both of these methods are used and the results are combined to measure the tt+ yield observed in data. The fraction of events passing the photon selection containing top quark pairs, referred to as the \top quark purity", can be measured by reconstructing the hadronically decaying top quark in the event. The M3 variable, de ned as the invariant mass of the three-jet combination that gives the highest vector sum of individual jet transverse momenta, is used for this purpose. Section 7 describes the t to the distribution of the M3 variable, used to distinguish top quark pair events from other backgrounds. Section 8 describes the measurement of the \photon purity", de ned as the fraction of reconstructed photons in the selection region, which come from genuine, isolated photons as opposed to misidenti ed photons originating from jets. A t to the photon isolation is used to measure this quantity, which can discriminate between the genuine photons expected from signal and the nonprompt photons from the tt background. The ts for extracting the top quark and photon purity are performed sequentially, and then the values are used in a likelihood function, from which a t is performed to extract the number of events that originate from the tt+ signal process. The likelihood t and extraction of the number of tt+ events are described in section 9. 6 Multijet and Z+jets background estimation The quantum chromodynamics (QCD) multijet process is not adequately modeled by simulation, so a data-based approach is applied to measure the shape and normalization of this background component. The shape of the QCD multijet background is taken from a sideband region in data. The sideband region is de ned by inverting the lepton relative isolation requirement, selecting leptons with a relative isolation greater than 0.25. Additionally, in the e+jets nal state the requirement on the multivariate-based electron identi cation is inverted, selecting electrons that would typically be identi ed as misidenti ed or nonprompt. This control region is dominated by QCD multijet events, with only minor contributions from other processes such as tt and W+jets. The small contribution in the control region from other processes is subtracted using simulation to provide shapes of the variable distributions used in the analysis. { 6 { The normalization of the QCD multijet background is measured through a binned T maximum-likelihood t to the pmiss distribution after the standard top quark selection is applied. The distribution of pTmiss is softer in the QCD multijet background than the other processes considered, and thus provides some discriminating power for this background. For the purposes of the t, the selection requirement on pmiss is removed, in order to improve the discriminating power of the t by bringing in more multijet events into the t region. Two distributions are used in the t, one for the multijet background and one for the contribution from all other processes. The distribution for the multijet background is taken from the shape found in the sideband control region, while the second distribution is T taken from the sum of all simulated events (which does not include the QCD background component). The t is performed separately in the e+jets and +jets nal states, and the results are used to scale the QCD multijet background distributions later in the analysis. The normalization and modeling of the Z+jets background distribution is taken from simulation, but the normalization is corrected by applying a scale factor derived from a t to data. In order to check the normalization, the selection is modi ed, selecting same- avor dilepton events, while keeping all other top quark selection requirements in place. A binned maximum-likelihood t is performed to the dilepton invariant mass for events passing this modi ed selection. The t is performed using two normalized distributions (templates) from simulation, a Z+jets template and a background template, which predominantly contains tt events. Scale factors for the normalization of the Z+jets background are derived from the t and applied to the simulation. 7 Estimate of top quark pair production The number of events containing top quark pairs, both after the top quark selection and for events passing the photon selection, are extracted through a binned maximum-likelihood t to the distribution of the M3 variable. In events with semileptonic decays of the top quark pair, the M3 variable provides a simple reconstruction of the hadronically decaying top quark, and has a distribution peaking at the mass of the top quark. Other processes have a wider M3 distribution. Two separate ts are performed to the M3 distribution. The rst t is performed after the top quark selection, to extract the total number of tt events passing the selection, Ntt. The second t is performed for events passing the photon selection in order to measure the top quark purity. 7.1 Measurement of the tt yield The t to the M3 distribution for events passing the top quark selection is used to extract the total number of top quark pairs, used for measuring the tt component of the cross section ratio. The t uses three templates: associated to top quark events (taken from tt and tt+ simulation), W+jets, and other background processes. The template for the other background processes is a combination of the data-based QCD multijet background and all other simulated samples. In the t, the normalizations of the top quark and W+jets templates are allowed to oat, while the normalizations of the other backgrounds { 7 { templates are kept xed. The QCD multijet background is normalized to the t to the pTmiss distribution, while other simulated samples are scaled to their theoretical cross sections. From the t, 162168 1565 (stat) and 219128 1869 (stat) tt events are observed in the e+jets and +jets nal states, respectively, consistent with the expected total number of tt events. The t results are used to scale the normalization of the tt and W+jets contributions in the rest of the analysis. Measurement of the top quark purity After the photon selection, a t to the M3 distribution is used to measure the top quark purity. The t uses three templates: associated to top quark events, W+ events, and the sum of all other processes. In the t, the normalizations of the top quark and W+ templates are varied, while the templates of all other processes remain xed. The top quark template contains simulated events for both tt+ and tt samples. Figure 2 shows the normalized M3 distributions for tt+ , tt, W+ , and other background processes. The backgrounds from non-top quark processes have a wider distribution in this variable, while the tt+ and tt processes peak near the top quark mass with a tail caused by events with an incorrect assignment of the jets. The relative contributions of the tt+ and tt samples to the top quark template are computed from the expected yields from simulation, though this does not change the shape of the top quark template as the two distributions are compatible. After the photon selection is applied, the distribution of the M3 variable in many of the background processes begins to su er from uctuations caused by the limited number of simulated events. Because the photon selection does not change the shape of the M3 distribution, the problem is solved by taking the shapes for the non-tt processes from the events after the top quark selection, while retaining the normalization of the samples observed after the photon selection is applied. result of the t. From the t result, the top quark purity is measured to be 0:70 with the expected values from simulation of 0:70 0:03 (stat) in the e+jets nal state and 0:72 0:02 (stat) in the +jets nal state, where the uncertainties are due to the limited number of simulated events. 8 Photon purity measurement Events are sorted into one of three categories based on the origin of their reconstructed photons. Genuine photons are those which are promptly produced, originating from nonhadronic sources. Misidenti ed photons can come from misreconstructed electrons, for which the track from the electron is not correctly reconstructed or properly matched to the energy cluster in the calorimeter, causing the electron to be reconstructed as a photon. Quark or gluon fragmentation and hadronization processes can be misidenti ed as photons or yield genuine photons, which for both cases are expected to be nonisolated, in contrast with promptly produced photons. The tt+ signal events predominantly fall within the rst category while the latter two categories are mostly composed of background events. { 8 { HJEP10(27)6 100 200 300 400 500 600 M3 (GeV) processes in a combination of the e+jets and +jets nal state after the photon selection. tt+γ tt W+γ Other backgrounds a combination of statistical and systematic uncertainties in the simulation. Simulated events can be placed in one of these three categories based on matching between the reconstructed and generated photons. Matching is performed based on the di erence between the reconstructed photon and the generated particles in both pT and the - phase space. If a reconstructed photon is matched to a generated photon from a nonhadronic source, it is classi ed in the rst category. Reconstructed photons that are not matched to a generated photon but instead are matched to a generated electron are classi ed as misidenti ed electrons, and placed in the second category. All other events, which are not matched to either a generated photon or electron, are considered to be nonprompt photons originating from hadronic activity and placed in the third category. { 9 { Photons in the last category, which are produced from hadronic activity, are typically less isolated than genuine photons or misidenti ed electrons. This di erence in the isolation distribution is used to measure the photon purity, de ned as the fraction of events with a photon originating from an isolated source (including both genuine photons and misidentied electrons). A binned maximum-likelihood t to the distribution of the charged-hadron isolation is used to measure the photon purity. Templates for the shape of the charged-hadron isolation for isolated photons (coming from either genuine photons or misidenti ed electrons) and nonprompt (nonisolated) photons are taken from data. The shape of the charged-hadron isolation for the isolated photon template is obtained using the random cone isolation method [38]. In this method, the sum of the transverse energy of PF charged-hadron candidates is measured within a cone of size R = 0:3 at the same value as the reconstructed photon, but in a random direction. Contributions to the isolation sum from charged hadrons coming from pileup interactions are subtracted from the energy in the cone. This gives an estimate of the isolation of a completely isolated particle. The shape of the charged-hadron isolation for nonprompt photon events is taken from a sideband region. The charged-hadron isolation of events with a photon having between 0.012 and 0.016 is used to construct the template for nonisolated photons. These events typically have nonprompt, hadronically produced photons. Comparisons of the distributions of the charged-hadron isolation templates for isolated and nonprompt photons extracted from the data-based method and the templates taken from simulation using the generated particle matching are shown in gure 4. In order to reduce the statistical uctuations in the background template, the selection requirement of the photon charged-hadron isolation being less than 5 GeV is relaxed during the t. Instead, the t is performed in the range of charged-hadron isolation less than 20 GeV, with all other photon selection requirements still in place. The distribution su ers from lower statistical precision at higher values of the isolation, so the distribution is rebinned with larger bins for higher isolation values and ner binning for lower values where the statistical precision is better. Figure 5 shows the result of the t of the photon chargedhadron isolation in a combination of the e+jets and +jets nal state. The photon purity is measured based on the fraction of events coming from isolated sources after the chargedhadron isolation requirement is put back in place. The photon purity is measured to be 0:57 0:06 (stat) and 0:53 The expected value for the photon purity in simulation, assuming the SM prediction for tt+ production, is 0:58 0:03 in the e+jets nal state and 0:57 0:02 in the +jets nal state. In order to correct the rate of misidenti ed electrons in simulation, the Z ! e+e process is used to measure events in which one of the electrons from the Z boson decay is misidenti ed as a photon. If the photon originates from a misidenti ed electron from the Z boson decay, the invariant mass of the combination of the electron and photon in the event will be near the Z boson mass. Under the nominal event selection described previously, the contribution from Z boson production is highly suppressed and does not provide a large enough sample of events to measure the electron misidenti cation rate accurately. In order to improve the statistical 10−4 .10−5 m CMS CMS hadron isolation, comparing templates derived from data to the distributions found from simulation in a combination of the e+jets and +jets nal states. The lower panel shows the ratio of the distributions derived from data to those found from simulation. 2ts000 1ne800 1vE600 1400 1200 1000 800 600 400 200 a t 1 aD0.50 CMS 10−3 .10−4 nal states. The uncertainty band shows the statistical uncertainties in the templates derived from data. The lower panel shows the ratio of the distribution observed in data to the sum of the templates scaled to the t result. precision, the event selection is modi ed by relaxing the requirement of having a b-tagged jet in the event, while keeping all other requirements the same. This enhances the contribution of Z ! e+e for this new selection. events. All steps for the multijet estimation and M3 t are repeated The removal of the b tagging requirement makes the Z boson mass peak much more pronounced in the e invariant mass distribution. This allows a template t to be performed, in order to estimate how well the misidenti cation of an electron as a photon is modeled in simulation. The t to the e invariant mass is performed using two templates, both derived from simulation. The rst template consists of events with Z bosons in which the reconstructed photon is matched to one of the electrons from the Z boson decay at the generator level. The second template consists of all other simulated samples not included in the previous template and the data-based multijet sample. The result of the t is shown Sample tt+ a t 1 aD0.520 CMS Data Sum Z→ee (e→γ) Background M(e,γ)(GeV) M(e,γ) (GeV) 8:5 215 60 11 16 31 342 0:9 13 15 6 4 18 28 | 0:5+00::75 | 321 237 75 60 16 54 29 31 823 17 14 25 15 5 30 7 18 52 935 40 60 modi ed event selection with the b tagging requirement relaxed. Distributions are shown scaled to the results of the t for Z ! ee (e ! ) and all other simulated samples (dashed lines), as well as the sum of the two samples (solid line). The lower panel shows the ratio of the data to the simulation scaled to the t results. Genuine photon Misid. electron Nonprompt photon Total 0:2 22 1:3 43 2:0 69 | | | | 0:1 3 1:1 28 1:3 29 in the e+jets channel. The data-based multijet sample is not expected to have signal photons or electrons. All uncertainties combine statistical and systematic contributions. in gure 6. A scale factor of 1:46 0:20 (stat) is found for simulated events with a misidenti ed electron. This scale factor is applied to all simulated events in which the photon is identi ed as originating from a misidenti ed electron. 9 The tt + yield measurement As previously mentioned, reconstructed photons originate from either a genuine photon, a misidenti ed electron, or a jet that produces a nonprompt photon. Di erent processes contribute to each of these three categories in di erent ways. For example, the tt+ and V+ processes predominantly produce genuine photons, while the tt and V+jets processes contribute to the nonprompt-photon or misidenti ed-electrons categories. The breakdown of the number of events in the three reconstructed photon categories from each of the tt+ 407 140 21 12 | | | | | 23 41 7 3 580 48 0:4 31 1:5 33 | | | | | | 0:3 5 1:3 5 11 291 9:0 57 1:4 9:6 25 36 440 1 16 6:7 14 0:9 5:8 13 20 33 418 322 149 57 23 10 38 36 1053 24 17 45 14 7 6 14 20 61 | 1136 +jets channel. The data-based multijet sample is not expected to have signal photons or electrons. All uncertainties combine statistical and systematic contributions. di erent simulated processes as well as the total number of expected and observed events are shown in tables 1 and 2 for the e+jets and The modeling of misidenti ed electrons has been corrected using the scale factor described in section 8, but the modeling of nonprompt photons from jets remains uncorrected. The normalization of the tt+jets, W+jets, Z+jets, and QCD samples have been cross-checked and corrected as described previously in sections 6 and 7. The contribution from single top quark processes is expected to be small and accurately modeled, and is left normalized to the theoretical cross sections. This leaves three major contributing sources, which have so far not been constrained and for which scale factors still need to be measured: tt+ , V+ , and photons originating from jets. e 2=2 where 2 is the sum of three terms: The three remaining scale factors, the scale factor on tt+ simulation (SFtt+ ), on V+ simulation (SFV+ ), and on simulation of photons originating from jets (SFjet! ), are derived by de ning a likelihood function based on the three previously measured quantities: the photon purity, edata; top quark purity, tdtata; and the number of events in data after the photon selection, N data. The likelihood function is de ned as L(SFtt+ ; SFV+ ; SFjet! ) = 2(SFtt+ ; SFV+ ; SFjet! ) = ( edata eMC)2 + ( tdtata tMt C)2 + 2 tt (N data N MC)2 2 N ; (9.1) where eMC; tMt C, and N MC are the photon purity, top quark purity, and the number of events expected from simulation, and tt , and N are the statistical uncertainties in the measured quantities. The value of the photon purity from simulation is taken to be the fraction of events in which the reconstructed photon originates from either a genuine photon or a misidenti ed electron. Similarly, the top quark purity in simulation is found as the fraction of the total simulated events coming from either the tt or tt+ processes. Because these three values depend on the relative contribution of events from the di erent processes, they are functions of the three scale factors, SFtt+ , SFV+ , and SFjet! . For 2 e e SFjet! of SFtt+ SFV+ example, the photon purity would be increased for larger values of SFtt+ or SFV+ whereas would increase the number of nonprompt photons and have the inverse e ect on the photon purity. Similarly the top quark purity would be increased for larger values or SFjet! (since tt is the largest contributor of nonprompt photons), whereas has the inverse e ect. The likelihood t is performed by scanning over the possible combinations of the three scale factors to and N MC, which most closely match the values observed in data, and thus returns the nd the one that results in values of eMC; tMt C; maximum likelihood value. The likelihood t is performed in the e+jets and +jets nal states individually, as well as in a combination of the two channels. The combination is performed by maximizing the product of the likelihood functions from the e+jets and +jets nal states. The scale factors obtained in the likelihood t are applied to the simulation to extract the number of tt+ events observed, Ntt+ . All tt+ events are scaled by SFtt+ , and those which fall within the nonprompt-photon category are additionally scaled by SFjet! . Applying the results of the t in a combination of the e+jets and +jets nal states, 780 119 (stat) tt+ events are observed, 338 53 (stat) events and 442 69 (stat) events in the e+jets and +jets nal states, respectively. The uncertainty comes predominantly from the statistical uncertainty in the results of the likelihood t. 10 Calculation of the cross section ratio The ducial tt+ cross section ( ttd+. ) and the inclusive tt+ cross section ( tt+ ) can be calculated based on the equations: tt+ d. = Ntt+ ; tt+ L tt+ = Ntt+ Att+ tt+ L = Atttt++ ; (10.1) where Ntt+ is the number of tt+ events observed, Att+ is the acceptance of tt+ events within the ducial phase space, tt+ is the e ciency of the tt+ selection within events in the acceptance region, and L is the integrated luminosity of the data set. The acceptance is determined at generator level, by requiring generated events to fall within the ducial phase space de ned for the analysis. Events are required to have exactly one generated prompt lepton in the ducial phase space. For electrons, this requires pT > 35 GeV and j j < 2:5 while not falling in the region 1:44 < j j < 1:56. The visible phase space for muons is de ned as pT > 26 GeV and j j < 2:5. Events are required to have at least three generated jets with pT > 30 GeV and j j < 2:4. In order to replicate the pmiss requirement, the vector sum of the pT of generated neutrinos is required to be greater T than 20 GeV. Lastly, events are required to have a generated photon with pT > 25 GeV and j j < 1:44. The acceptance can be split into two components: the one coming from the branching fraction of tt+ to the e+jets or +jets channels, and the one coming from the kinematic phase space requirements. The kinematic acceptance is measured by the number of events passing the kinematic phase space requirements described above divided by the number of events generated in the e+jets and +jets nal states. Kinematic acceptance E ciency 0:2380 0:1198 0:0014 0:0071 0:2551 0:1268 0:0014 0:0070 The e ciency is calculated as the ratio of reconstructed events that pass the event selection over the number of events generated in the ducial phase space. This accounts for the migration of events into and out of the ducial phase space, and includes the e ciencies of the trigger requirement, object identi cation and reconstruction, and the event selection. The measured values for the acceptance and e ciency of the tt+ selection in the e+jets and +jets channels are given in table 3. In order to reduce the e ect of systematic uncertainties that similarly a ect all tt+jets production modes, the ratio of the cross section of ducial tt+ production to the inclusive tt production cross section is calculated as R = d tt+ tt = Ntt+ tt+ tttopAtttop ; Ntt (10.2) where Ntt is the number of tt events passing the top quark selection, and ttotp and Atttop are the e ciency and acceptance of top quark selection for tt events. The value of tttop Atttop is determined from simulation to be 0:034 in the e+jets nal state and 0:046 in the +jets nal state with negligible statistical uncertainties. 11 Sources of systematic uncertainty The e ects of the systematic uncertainties are estimated by varying the simulated samples according to the uncertainty and repeating the measurement. The top quark purity measurement, photon purity measurement, and likelihood t are repeated for each source of systematic uncertainty and the new value of the cross section ratio is compared to the nominal value. In this way, an estimate of the e ect each source of systematic uncertainty has on the nal result is found. Table 4 lists the uncertainties in decreasing order of their e ect on the cross section ratio, as found through the combination of the e+jets and +jets nal states. The statistical uncertainty in the number of signal events found after maximizing the likelihood t described in section 9, dominates the determination of the cross section for tt+ . It includes the uncertainties in the measurement of the photon purity, top quark purity after photon selection, and the statistical uncertainty from the observed number of events in data. The contribution from each of these three portions is estimated individually by performing the likelihood t in which the uncertainties in these parameters are set to zero one at a time. This e ectively xes the value to the measured value. The change in the SFtt+ uncertainty (which is roughly 14% in the standard likelihood t) can be attributed to the xed parameter. The uncertainty is dominated by the top quark purity and photon purity uncertainties, which contribute 10% and 9%, respectively. The statistical uncertainty caused by the limited number of events in data is approximately 4.8%. The uncertainties in the energy of reconstructed objects in the event are taken into account by scaling the energies of reconstructed objects in simulation up and down by the uncertainties in their corrections. The uncertainties in the jet energy scale (JES) and jet energy resolution (JER) [35] are applied to the reconstructed jets and the e ect is propagated to the calculation of pTmiss. Similarly the uncertainty due to the photon energy is found by scaling the energy of reconstructed photons up and down by 1%, and the measurement is repeated [12]. The uncertainty due to the lepton energy scale is found by varying the pT of the electrons and muons in the event by 1% in the e+jets and +jets nal states, respectively [32, 39]. A 50% uncertainty is assigned to the normalization of the data-based multijet sample T derived from the t to the pmiss distributions. Additionally, a 20% normalization uncertainty is applied to the backgrounds that are xed to their theoretical cross sections in the M3 t (described in section 7). The systematic uncertainty due to the scale factor for Z+jets simulation (described in section 6) is applied by adjusting the scale factor up and down by its uncertainty. The uncertainty in the e ciency of the b tagging algorithm is taken into account by varying the b tagging scale factors up and down by their uncertainties [37]. Di erences between the distribution of the pT of the top quarks in data and simulation are taken into account by applying a reweighting based on the pT of the generated top quarks and treating the di erence from the nominal sample as a systematic uncertainty (\top quark pT reweighting") [40]. The uncertainty in the pileup correction is found by recalculating the pileup distribution in data with a plus and minus 5% change to the total inelastic protonproton cross section [41], and using these new distributions to reweight the simulation. The uncertainty in the factorization and renormalization scales is taken into account by simulating the tt+ and tt+jets processes with the scales doubled and halved compared to the nominal value of F = R = Q = p mt2 + p2T (where the sum is taken over all nal state partons). The uncertainty in the matching of partons at ME level to the parton shower (PS) is found by simulating tt+ and tt+jets processes with the threshold used for matching doubled and halved from the nominal value of 20 GeV. The uncertainty arising from the choice of the top quark mass used in simulation is measured by simulating the samples with a value of mt varied up and down by 1 GeV from its central value of mt = 172:5 GeV. 12 Results The ratio of the ducial cross section of tt+ to tt production is found to be R = (5:7 1:8) the 10 4 (stat+syst) in the e+jets nal state and R = (4:7 1:3) 10 4 (stat+syst) in +jets nal state. The value of the ducial tt+ cross section can be extracted from the cross section ratio using the measured tt cross section of 244:9 6:4 (lumi) pb [24]. Multiplying the cross section ratio by the measured tt cross section Source Statistical likelihood t Top quark mass JES JER Fact. and renorm. scale ME/PS matching threshold Photon energy scale Multijet estimate Electron misid. rate Z+jets scale factor Pileup Background normalization Top quark pT reweighting b tagging scale factor Muon e ciency Electron e ciency PDFs Total Muon energy scale Electron energy scale Uncertainty (%) semileptonic nal states [42]. The value of the cross section times the branching fraction in the lepton+jets nal states can be extrapolated from the ducial cross section by dividing by the kinematic acceptance. The kinematic acceptances (as given in section 10) are found to be 0:2380 0:0014 and 0:2551 0:0014 in the e+jets and +jets nal states. This gives a cross section times branching fraction of tt+ B = 582 187 fb in the e+jets nal state and 453 124 fb +jets nal state. These values are in agreement with theoretical prediction of 71(scales) 30 (PDFs) fb for the cross section times branching fraction of each of the The combination of the e+jets and +jets channels results in a cross section ratio per semileptonic nal state of (5:2 1:1) 10 4 (stat+syst). This results in a value of 127 27 (stat+syst) fb for the ducial tt+ cross section. When extrapolated to the cross section times branching fraction by dividing by the kinematic acceptance, the result is tt+ B = 515 108 fb per lepton+jets nal state, in good agreement with the theoretical prediction. Table 5 summarizes the measured ratios and cross sections for the e+jets and +jets nal states as well as the combination. HJEP10(27)6 1:8) 1:3) 1:1) | ×103 CMS passing the photon selection. The lower panel shows the ratio of the data to the prediction from simulation. The uncertainty band is a combination of statistical and systematic uncertainties in the simulation. The distributions of the transverse momentum and absolute value of the pseudorapidity of the photon candidate are shown in gures 7 and 8, scaled to the results of the likelihood t. While the statistical precision of this analysis currently limits the ability to perform a di erential measurement of the tt+ cross section, there is the potential to measure the di erential cross section in the future in both of these variables. 13 Summary The results of a measurement of the production of a top quark-antiquark (tt) pair produced in association with a photon have been presented. The measurement is performed using 19.7 fb 1 of data collected by the CMS detector at a center-of-mass energy of 8 TeV. The analysis has been performed in the semileptonic e+jets and +jets decay channels. The ratio of the tt+ to tt production cross sections has been measured to be R = tt+ = tt = (5:2 1:1) 10 4. By multiplying the measured ratio by the previously measured value of the tt cross section, the ducial cross section for tt+ production of 127 27 fb has been found for events in the e+jets and +jets nal states. The measured values are in agreement with the theoretical predictions. CMS / ts500 e/μ+jets in600 b n 300 200 100 W/Z+γ W/Z+jets simulation, scaled to the result of the likelihood t in a combination of the e+jets and +jets channels for events passing the photon selection. The lower panel shows the ratio of the data to the prediction from simulation. The uncertainty band is a combination of statistical and systematic uncertainties in the simulation. Acknowledgments We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC and thank the technical and administrative sta s at CERN and at other CMS institutes for their contributions to the success of the CMS e ort. In addition, we gratefully acknowledge the computing centres and personnel of the Worldwide LHC Computing Grid for delivering so e ectively the computing infrastructure essential to our analyses. Finally, we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: BMWFW and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RPF (Cyprus); SENESCYT (Ecuador); MoER, ERC IUT, and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM (Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON, RosAtom, RAS, RFBR and RAEP (Russia); MESTD (Serbia); SEIDI, CPAN, PCTI and FEDER (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR, and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC (United Kingdom); DOE and NSF (U.S.A.). Individuals have received support from the Marie-Curie programme and the European Research Council and Horizon 2020 Grant, contract No. 675440 (European Union); the Leventis Foundation; the A. P. Sloan Foundation; the Alexander von Humboldt Foundation; the Belgian Federal Science Policy O ce; the Fonds pour la Formation a la Recherche dans l'Industrie et dans l'Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); the Ministry of Education, Youth and Sports (MEYS) of the Czech Republic; the Council of Science and Industrial Research, India; the HOMING PLUS programme of the Foundation for Polish Science, co nanced from European Union, Regional Development Fund, the Mobility Plus programme of the Ministry of Science and Higher Education, the National Science Center (Poland), contracts Harmonia 2014/14/M/ST2/00428, Opus 2014/13/B/ST2/02543, 2014/15/B/ST2/03998, and 2015/19/B/ST2/02861, Sonata-bis 2012/07/E/ST2/01406; the National Priorities Research Program by Qatar National Research Fund; the Programa Clar n-COFUND del Principado de Asturias; the Thalis and Aristeia programmes co nanced by EU-ESF and the Greek NSRF; the Rachadapisek Sompot Fund for Postdoctoral Fellowship, Chulalongkorn University and the Chulalongkorn Academic into Its 2nd Century Project Advancement Project (Thailand); and the Welch Foundation, contract C-1845. 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Godinovic, D. Lelas, I. Puljak, P.M. Ribeiro Cipriano, T. Sculac University of Split, Faculty of Science, Split, Croatia Z. Antunovic, M. Kovac Institute Rudjer Boskovic, Zagreb, Croatia V. Brigljevic, D. Ferencek, K. Kadija, B. Mesic, T. Susa University of Cyprus, Nicosia, Cyprus A. Attikis, G. Mavromanolakis, J. Mousa, C. Nicolaou, F. Ptochos, P.A. Razis, H. Rykaczewski, D. Tsiakkouri Charles University, Prague, Czech Republic M. Finger8, M. Finger Jr.8 Universidad San Francisco de Quito, Quito, Ecuador E. Carrera Jarrin Academy of Scienti c Research and Technology of the Arab Republic of Egypt, Egyptian Network of High Energy Physics, Cairo, Egypt E. El-khateeb9, S. Elgammal10, A. Mohamed11 National Institute of Chemical Physics and Biophysics, Tallinn, Estonia M. Kadastik, L. Perrini, M. Raidal, A. Tiko, C. Veelken Department of Physics, University of Helsinki, Helsinki, Finland P. Eerola, J. Pekkanen, M. Voutilainen Helsinki Institute of Physics, Helsinki, Finland J. Harkonen, T. Jarvinen, V. Karimaki, R. Kinnunen, T. Lampen, K. Lassila-Perini, S. Lehti, T. Linden, P. Luukka, J. Tuominiemi, E. Tuovinen, L. Wendland Lappeenranta University of Technology, Lappeenranta, Finland J. Talvitie, T. Tuuva IRFU, CEA, Universite Paris-Saclay, Gif-sur-Yvette, France M. Besancon, F. Couderc, M. Dejardin, D. Denegri, B. Fabbro, J.L. Faure, C. Favaro, F. Ferri, S. Ganjour, S. Ghosh, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry, I. Kucher, E. Locci, M. Machet, J. Malcles, J. Rander, A. Rosowsky, M. Titov Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS/IN2P3, Universite Paris-Saclay, Palaiseau, France A. Abdulsalam, I. Antropov, S. Ba oni, F. Beaudette, P. Busson, L. Cadamuro, E. Chapon, C. Charlot, O. Davignon, R. Granier de Cassagnac, M. Jo, S. Lisniak, P. Mine, M. Nguyen, C. Ochando, G. Ortona, P. Paganini, P. Pigard, S. Regnard, R. Salerno, Y. Sirois, A.G. Stahl Leiton, T. Strebler, Y. Yilmaz, A. Zabi, A. Zghiche Universite de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg, France S. Gadrat J.-L. Agram12, J. Andrea, A. Aubin, D. Bloch, J.-M. Brom, M. Buttignol, E.C. Chabert, N. Chanon, C. Collard, E. Conte12, X. Coubez, J.-C. Fontaine12, D. Gele, U. Goerlach, A.-C. Le Bihan, P. Van Hove Centre de Calcul de l'Institut National de Physique Nucleaire et de Physique des Particules, CNRS/IN2P3, Villeurbanne, France Universite de Lyon, Universite Claude Bernard Lyon 1, CNRS-IN2P3, Institut de Physique Nucleaire de Lyon, Villeurbanne, France S. Beauceron, C. Bernet, G. Boudoul, C.A. Carrillo Montoya, R. Chierici, D. Contardo, B. Courbon, P. Depasse, H. El Mamouni, J. Fay, S. Gascon, M. Gouzevitch, G. Grenier, B. Ille, F. Lagarde, I.B. Laktineh, M. Lethuillier, L. Mirabito, A.L. Pequegnot, S. Perries, A. Popov13, D. Sabes, V. Sordini, M. Vander Donckt, P. Verdier, S. Viret Georgian Technical University, Tbilisi, Georgia A. Khvedelidze8 D. Lomidze Tbilisi State University, Tbilisi, Georgia RWTH Aachen University, I. Physikalisches Institut, Aachen, Germany C. Autermann, S. Beranek, L. Feld, M.K. Kiesel, K. Klein, M. Lipinski, M. Preuten, C. Schomakers, J. Schulz, T. Verlage RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany A. Albert, M. Brodski, E. Dietz-Laursonn, D. Duchardt, M. Endres, M. Erdmann, S. Erdweg, T. Esch, R. Fischer, A. Guth, M. Hamer, T. Hebbeker, C. Heidemann, K. Hoepfner, S. Knutzen, M. Merschmeyer, A. Meyer, P. Millet, S. Mukherjee, M. Olschewski, K. Padeken, T. Pook, M. Radziej, H. Reithler, M. Rieger, F. Scheuch, L. Sonnenschein, D. Teyssier, S. Thuer RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany V. Cherepanov, G. Flugge, B. Kargoll, T. Kress, A. Kunsken, J. Lingemann, T. Muller, A. Nehrkorn, A. Nowack, C. Pistone, O. Pooth, A. Stahl14 Deutsches Elektronen-Synchrotron, Hamburg, Germany M. Aldaya Martin, T. Arndt, C. Asawatangtrakuldee, K. Beernaert, O. Behnke, U. Behrens, A.A. Bin Anuar, K. Borras15, A. Campbell, P. Connor, C. ContrerasCampana, F. Costanza, C. Diez Pardos, G. Dolinska, G. Eckerlin, D. Eckstein, T. Eichhorn, E. Eren, E. Gallo16, J. Garay Garcia, A. Geiser, A. Gizhko, J.M. Grados Luyando, A. Grohsjean, P. Gunnellini, A. Harb, J. Hauk, M. Hempel17, H. Jung, A. Kalogeropoulos, O. Karacheban17, M. Kasemann, J. Keaveney, C. Kleinwort, I. Korol, D. Krucker, W. Lange, A. Lelek, T. Lenz, J. Leonard, K. Lipka, A. Lobanov, W. Lohmann17, R. Mankel, I.-A. Melzer-Pellmann, A.B. Meyer, G. Mittag, J. Mnich, A. Mussgiller, D. Pitzl, R. Placakyte, A. Raspereza, B. Roland, M.O . Sahin, P. Saxena, T. SchoernerSadenius, S. Spannagel, N. Stefaniuk, G.P. Van Onsem, R. Walsh, C. Wissing University of Hamburg, Hamburg, Germany V. Blobel, M. Centis Vignali, A.R. Draeger, T. Dreyer, E. Garutti, D. Gonzalez, J. Haller, M. Ho mann, A. Junkes, R. Klanner, R. Kogler, N. Kovalchuk, T. Lapsien, I. Marchesini, D. Marconi, M. Meyer, M. Niedziela, D. Nowatschin, F. Pantaleo14, T. Pei er, A. Perieanu, C. Scharf, P. Schleper, A. Schmidt, S. Schumann, J. Schwandt, H. Stadie, G. Steinbruck, F.M. Stober, M. Stover, H. Tholen, D. Troendle, E. Usai, L. Vanelderen, A. Vanhoefer, B. Vormwald Institut fur Experimentelle Kernphysik, Karlsruhe, Germany M. Akbiyik, C. Barth, S. Baur, C. Baus, J. Berger, E. Butz, R. Caspart, T. Chwalek, F. Colombo, W. De Boer, A. Dierlamm, S. Fink, B. Freund, R. Friese, M. Gi els, A. Gilbert, P. Goldenzweig, D. Haitz, F. Hartmann14, S.M. Heindl, U. Husemann, I. Katkov13, S. Kudella, H. Mildner, M.U. Mozer, Th. Muller, M. Plagge, G. Quast, K. Rabbertz, S. Rocker, F. Roscher, M. Schroder, I. Shvetsov, G. Sieber, H.J. Simonis, R. Ulrich, S. Wayand, M. Weber, T. Weiler, S. Williamson, C. Wohrmann, R. Wolf Institute of Nuclear and Particle Physics (INPP), NCSR Demokritos, Aghia Paraskevi, Greece I. Topsis-Giotis G. Anagnostou, G. Daskalakis, T. Geralis, V.A. Giakoumopoulou, A. Kyriakis, D. Loukas, National and Kapodistrian University of Athens, Athens, Greece S. Kesisoglou, A. Panagiotou, N. Saoulidou, E. Tziaferi University of Ioannina, Ioannina, Greece I. Evangelou, G. Flouris, C. Foudas, P. Kokkas, N. Loukas, N. Manthos, I. Papadopoulos, MTA-ELTE Lendulet CMS Particle and Nuclear Physics Group, Eotvos Lorand University, Budapest, Hungary N. Filipovic, G. Pasztor Wigner Research Centre for Physics, Budapest, Hungary G. Bencze, C. Hajdu, D. Horvath18, F. Sikler, V. Veszpremi, G. Vesztergombi19, A.J. ZsigInstitute of Nuclear Research ATOMKI, Debrecen, Hungary N. Beni, S. Czellar, J. Karancsi20, A. Makovec, J. Molnar, Z. Szillasi Institute of Physics, University of Debrecen, Debrecen, Hungary M. Bartok19, P. Raics, Z.L. Trocsanyi, B. Ujvari Indian Institute of Science (IISc), Bangalore, India J.R. Komaragiri National Institute of Science Education and Research, Bhubaneswar, India S. Bahinipati21, S. Bhowmik22, S. Choudhury23, P. Mal, K. Mandal, A. Nayak24, D.K. Sahoo21, N. Sahoo, S.K. Swain Panjab University, Chandigarh, India S. Bansal, S.B. Beri, V. Bhatnagar, U. Bhawandeep, R. Chawla, A.K. Kalsi, A. Kaur, M. Kaur, R. Kumar, P. Kumari, A. Mehta, M. Mittal, J.B. Singh, G. Walia University of Delhi, Delhi, India Ashok Kumar, A. Bhardwaj, B.C. Choudhary, R.B. Garg, S. Keshri, S. Malhotra, M. Naimuddin, K. Ranjan, R. Sharma, V. Sharma Saha Institute of Nuclear Physics, HBNI, Kolkata, India R. Bhattacharya, S. Bhattacharya, K. Chatterjee, S. Dey, S. Dutt, S. Dutta, S. Ghosh, N. Majumdar, A. Modak, K. Mondal, S. Mukhopadhyay, S. Nandan, A. Purohit, A. Roy, D. Roy, S. Roy Chowdhury, S. Sarkar, M. Sharan, S. Thakur Indian Institute of Technology Madras, Madras, India P.K. Behera Bhabha Atomic Research Centre, Mumbai, India R. Chudasama, D. Dutta, V. Jha, V. Kumar, A.K. Mohanty14, P.K. Netrakanti, L.M. Pant, P. Shukla, A. Topkar Tata Institute of Fundamental Research-A, Mumbai, India T. Aziz, S. Dugad, G. Kole, B. Mahakud, S. Mitra, G.B. Mohanty, B. Parida, N. Sur, B. Sutar Tata Institute of Fundamental Research-B, Mumbai, India S. Banerjee, R.K. Dewanjee, S. Ganguly, M. Guchait, Sa. Jain, S. Kumar, M. Maity22, G. Majumder, K. Mazumdar, T. Sarkar22, N. Wickramage25 Indian Institute of Science Education and Research (IISER), Pune, India S. Chauhan, S. Dube, V. Hegde, A. Kapoor, K. Kothekar, S. Pandey, A. Rane, S. Sharma Institute for Research in Fundamental Sciences (IPM), Tehran, Iran S. Chenarani26, E. Eskandari Tadavani, S.M. Etesami26, M. Khakzad, M. Mohammadi Najafabadi, M. Naseri, S. Paktinat Mehdiabadi27, F. Rezaei Hosseinabadi, B. Safarzadeh28, M. Zeinali University College Dublin, Dublin, Ireland M. Felcini, M. Grunewald INFN Sezione di Bari a, Universita di Bari b, Politecnico di Bari c, Bari, Italy M. Abbresciaa;b, C. Calabriaa;b, C. Caputoa;b, A. Colaleoa, D. Creanzaa;c, L. Cristellaa;b, N. De Filippisa;c, M. De Palmaa;b, L. Fiorea, G. Iasellia;c, G. Maggia;c, M. Maggia, G. Minielloa;b, S. Mya;b, S. 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Bacchettaa, L. Benatoa;b, D. Biselloa;b, A. Bolettia;b, R. Carlina;b, A. Carvalho Antunes De Oliveiraa;b, P. Checchiaa, M. Dall'Ossoa;b, P. De Castro Manzanoa, T. Dorigoa, F. Fanzagoa, F. Gasparinia;b, F. Gonellaa, S. Lacapraraa, M. Margonia;b, A.T. Meneguzzoa;b, J. Pazzinia;b, N. Pozzobona;b, P. Ronchesea;b, F. Simonettoa;b, E. Torassaa, S. Venturaa, M. Zanettia;b, P. Zottoa;b, G. Zumerlea;b INFN Sezione di Pavia a, Universita di Pavia b, Pavia, Italy A. Braghieria, F. Fallavollitaa;b, A. Magnania;b, P. Montagnaa;b, S.P. Rattia;b, V. Rea, C. Riccardia;b, P. Salvinia, I. Vaia;b, P. Vituloa;b INFN Sezione di Perugia a, Universita di Perugia b, Perugia, Italy L. Alunni Solestizia;b, G.M. Bileia, D. Ciangottinia;b, L. Fanoa;b, P. Laricciaa;b, R. Leonardia;b, G. Mantovania;b, V. Mariania;b, M. Menichellia, A. Sahaa, A. Santocchiaa;b INFN Sezione di Pisa a, Universita di Pisa b, Scuola Normale Superiore di Pisa c, Pisa, Italy K. Androsova;29, P. Azzurria;14, G. Bagliesia, J. 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Pachera;b, N. Pastronea, M. Pelliccionia, G.L. Pinna Angionia;b, F. Raveraa;b, A. Romeroa;b, M. Ruspaa;c, R. Sacchia;b, K. Shchelinaa;b, V. Solaa, A. Solanoa;b, A. Staianoa, P. Traczyka;b INFN Sezione di Trieste a, Universita di Trieste b, Trieste, Italy S. Belfortea, M. Casarsaa, F. Cossuttia, G. Della Riccaa;b, A. Zanettia Kyungpook National University, Daegu, Korea D.H. Kim, G.N. Kim, M.S. Kim, S. Lee, S.W. Lee, Y.D. Oh, S. Sekmen, D.C. Son, HJEP10(27)6 Y.C. Yang A. Lee Kwangju, Korea H. Kim Chonbuk National University, Jeonju, Korea Chonnam National University, Institute for Universe and Elementary Particles, Hanyang University, Seoul, Korea J.A. Brochero Cifuentes, T.J. Kim Korea University, Seoul, Korea J. Lim, S.K. Park, Y. Roh Seoul National University, Seoul, Korea G.B. Yu University of Seoul, Seoul, Korea S. Cho, S. Choi, Y. Go, D. Gyun, S. Ha, B. Hong, Y. Jo, Y. Kim, K. Lee, K.S. Lee, S. Lee, J. Almond, J. Kim, H. Lee, S.B. Oh, B.C. Radburn-Smith, S.h. Seo, U.K. Yang, H.D. 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Krofcheck P.H. Butler University of Auckland, Auckland, New Zealand University of Canterbury, Christchurch, New Zealand National Centre for Physics, Quaid-I-Azam University, Islamabad, Pakistan A. Ahmad, M. Ahmad, Q. Hassan, H.R. Hoorani, W.A. Khan, A. Saddique, M.A. Shah, M. Shoaib, M. Waqas National Centre for Nuclear Research, Swierk, Poland H. Bialkowska, M. Bluj, B. Boimska, T. Frueboes, M. Gorski, M. Kazana, K. Nawrocki, K. Romanowska-Rybinska, M. Szleper, P. Zalewski Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland K. Bunkowski, A. Byszuk34, K. Doroba, A. Kalinowski, M. Konecki, J. Krolikowski, M. Misiura, M. Olszewski, M. Walczak Laboratorio de Instrumentac~ao e F sica Experimental de Part culas, Lisboa, Portugal P. Bargassa, C. Beir~ao Da Cruz E Silva, B. Calpas, A. Di Francesco, P. Faccioli, P.G. Ferreira Parracho, M. Gallinaro, J. Hollar, N. Leonardo, L. Lloret Iglesias, M.V. Nemallapudi, J. Rodrigues Antunes, J. Seixas, O. Toldaiev, D. Vadruccio, J. Varela Joint Institute for Nuclear Research, Dubna, Russia S. Afanasiev, P. Bunin, M. Gavrilenko, I. Golutvin, I. Gorbunov, A. Kamenev, V. Karjavin, A. Lanev, A. Malakhov, V. Matveev35;36, V. Palichik, V. Perelygin, S. Shmatov, S. Shulha, N. Skatchkov, V. Smirnov, N. Voytishin, A. Zarubin Petersburg Nuclear Physics Institute, Gatchina (St. Petersburg), Russia L. Chtchipounov, V. Golovtsov, Y. Ivanov, V. Kim37, E. Kuznetsova38, V. Murzin, V. Oreshkin, V. Sulimov, A. Vorobyev Institute for Nuclear Research, Moscow, Russia Yu. Andreev, A. Dermenev, S. Gninenko, N. Golubev, A. Karneyeu, M. Kirsanov, N. Krasnikov, A. Pashenkov, D. Tlisov, A. Toropin Institute for Theoretical and Experimental Physics, Moscow, Russia V. Epshteyn, V. Gavrilov, N. Lychkovskaya, V. Popov, I. Pozdnyakov, G. Safronov, A. Spiridonov, M. Toms, E. Vlasov, A. Zhokin Moscow Institute of Physics and Technology, Moscow, Russia T. Aushev, A. Bylinkin36 National Research Nuclear University 'Moscow Engineering Physics Institute' (MEPhI), Moscow, Russia R. Chistov39, M. Danilov39, V. Rusinov P.N. Lebedev Physical Institute, Moscow, Russia V. Andreev, M. Azarkin36, I. Dremin36, M. Kirakosyan, A. Leonidov36, A. Terkulov Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia P. Volkov A. Baskakov, A. Belyaev, E. Boos, V. Bunichev, M. Dubinin40, L. Dudko, V. Klyukhin, O. Kodolova, N. Korneeva, I. Lokhtin, I. Miagkov, S. Obraztsov, M. Per lov, V. Savrin, Novosibirsk State University (NSU), Novosibirsk, Russia V. Blinov41, Y.Skovpen41, D. Shtol41 State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, Russia I. Azhgirey, I. Bayshev, S. Bitioukov, D. Elumakhov, V. Kachanov, A. Kalinin, D. Konstantinov, V. Krychkine, V. Petrov, R. Ryutin, A. Sobol, S. Troshin, N. Tyurin, A. Uzunian, A. Volkov University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, Belgrade, Serbia P. Adzic42, P. Cirkovic, D. Devetak, M. Dordevic, J. Milosevic, V. Rekovic Centro de Investigaciones Energeticas Medioambientales y Tecnologicas (CIEMAT), Madrid, Spain J. Alcaraz Maestre, M. Barrio Luna, E. Calvo, M. Cerrada, M. Chamizo Llatas, N. Colino, B. De La Cruz, A. Delgado Peris, A. Escalante Del Valle, C. Fernandez Bedoya, J.P. Fernandez Ramos, J. Flix, M.C. Fouz, P. Garcia-Abia, O. Gonzalez Lopez, S. Goy Lopez, J.M. Hernandez, M.I. Josa, E. Navarro De Martino, A. Perez-Calero Yzquierdo, J. Puerta Pelayo, A. Quintario Olmeda, I. Redondo, L. Romero, M.S. Soares Universidad Autonoma de Madrid, Madrid, Spain J.F. de Troconiz, M. Missiroli, D. Moran Universidad de Oviedo, Oviedo, Spain J. Cuevas, J. Fernandez Menendez, I. Gonzalez Caballero, J.R. Gonzalez Fernandez, E. Palencia Cortezon, S. Sanchez Cruz, I. Suarez Andres, P. Vischia, J.M. Vizan Garcia Instituto de F sica de Cantabria (IFCA), CSIC-Universidad de Cantabria, Santander, Spain I.J. Cabrillo, A. Calderon, E. Curras, M. Fernandez, J. Garcia-Ferrero, G. Gomez, A. Lopez Virto, J. Marco, C. Martinez Rivero, F. Matorras, J. Piedra Gomez, T. Rodrigo, A. RuizJimeno, L. Scodellaro, N. Trevisani, I. Vila, R. Vilar Cortabitarte CERN, European Organization for Nuclear Research, Geneva, Switzerland D. Abbaneo, E. Au ray, G. Auzinger, P. Baillon, A.H. Ball, D. Barney, P. Bloch, A. Bocci, C. Botta, T. Camporesi, R. Castello, M. Cepeda, G. Cerminara, Y. Chen, D. d'Enterria, A. Dabrowski, V. Daponte, A. David, M. De Gruttola, A. De Roeck, E. Di Marco43, M. Dobson, B. Dorney, T. du Pree, D. Duggan, M. Dunser, N. Dupont, A. Elliott-Peisert, P. Everaerts, S. Fartoukh, G. Franzoni, J. Fulcher, W. Funk, D. Gigi, K. Gill, M. Girone, F. Glege, D. Gulhan, S. Gundacker, M. Gutho , P. Harris, J. Hegeman, V. Innocente, P. Janot, J. Kieseler, H. Kirschenmann, V. Knunz, A. Kornmayer14, M.J. Kortelainen, K. Kousouris, M. Krammer1, C. Lange, P. Lecoq, C. Lourenco, M.T. Lucchini, L. Malgeri, M. Mannelli, A. Martelli, F. Meijers, J.A. Merlin, S. Mersi, E. Meschi, P. Milenovic44, F. Moortgat, S. Morovic, M. Mulders, H. Neugebauer, S. Orfanelli, L. Orsini, L. Pape, E. Perez, M. Peruzzi, A. Petrilli, G. Petrucciani, A. Pfei er, M. Pierini, A. Racz, T. Reis, G. Rolandi45, M. Rovere, H. Sakulin, J.B. Sauvan, C. Schafer, C. Schwick, M. Seidel, A. Sharma, P. Silva, P. Sphicas46, J. Steggemann, M. Stoye, Y. Takahashi, M. Tosi, D. Treille, A. Triossi, A. Tsirou, V. Veckalns47, G.I. Veres19, M. Verweij, N. Wardle, H.K. Wohri, A. Zagozdzinska34, W.D. Zeuner Paul Scherrer Institut, Villigen, Switzerland W. Bertl, K. Deiters, W. Erdmann, R. Horisberger, Q. Ingram, H.C. Kaestli, D. Kotlinski, U. Langenegger, T. Rohe, S.A. Wiederkehr Institute for Particle Physics, ETH Zurich, Zurich, Switzerland F. Bachmair, L. Bani, L. Bianchini, B. Casal, G. Dissertori, M. Dittmar, M. Donega, C. Grab, C. Heidegger, D. Hits, J. Hoss, G. Kasieczka, W. Lustermann, B. Mangano, M. Marionneau, P. Martinez Ruiz del Arbol, M. Masciovecchio, M.T. Meinhard, D. Meister, F. Micheli, P. Musella, F. Nessi-Tedaldi, F. Pandol , J. Pata, F. Pauss, G. Perrin, L. Perrozzi, M. Quittnat, M. Rossini, M. Schonenberger, A. Starodumov48, V.R. Tavolaro, K. Theo latos, R. Wallny Universitat Zurich, Zurich, Switzerland T.K. Aarrestad, C. Amsler49, L. Caminada, M.F. Canelli, A. De Cosa, C. Galloni, A. Hinzmann, T. Hreus, B. Kilminster, J. Ngadiuba, D. Pinna, G. Rauco, P. Robmann, D. Salerno, C. Seitz, Y. Yang, A. Zucchetta National Central University, Chung-Li, Taiwan V. Candelise, T.H. Doan, Sh. Jain, R. Khurana, M. Konyushikhin, C.M. Kuo, W. Lin, A. Pozdnyakov, S.S. Yu National Taiwan University (NTU), Taipei, Taiwan Arun Kumar, P. Chang, Y.H. Chang, Y. Chao, K.F. Chen, P.H. Chen, F. Fiori, W.-S. Hou, Y. Hsiung, Y.F. Liu, R.-S. Lu, M. Min~ano Moya, E. Paganis, A. Psallidas, J.f. Tsai Chulalongkorn University, Faculty of Science, Department of Physics, Bangkok, Thailand Turkey B. Asavapibhop, G. Singh, N. Srimanobhas, N. Suwonjandee Cukurova University, Physics Department, Science and Art Faculty, Adana, A. Adiguzel, S. Cerci50, S. Damarseckin, Z.S. Demiroglu, C. Dozen, I. Dumanoglu, S. Girgis, G. Gokbulut, Y. Guler, I. Hos51, E.E. Kangal52, O. Kara, U. Kiminsu, M. Oglakci, G. Onengut53, K. Ozdemir54, D. Sunar Cerci50, B. Tali50, H. Topakli55, S. Turkcapar, I.S. Zorbakir, C. Zorbilmez Middle East Technical University, Physics Department, Ankara, Turkey B. Bilin, S. Bilmis, B. Isildak56, G. Karapinar57, M. Yalvac, M. Zeyrek Bogazici University, Istanbul, Turkey E. Gulmez, M. Kaya58, O. Kaya59, E.A. Yetkin60, T. Yetkin61 Istanbul Technical University, Istanbul, Turkey A. Cakir, K. Cankocak, S. Sen62 Institute for Scintillation Materials of National Academy of Science of Ukraine, Kharkov, Ukraine B. Grynyov Kharkov, Ukraine L. Levchuk, P. Sorokin National Scienti c Center, Kharkov Institute of Physics and Technology, University of Bristol, Bristol, United Kingdom R. Aggleton, F. Ball, L. Beck, J.J. Brooke, D. Burns, E. Clement, D. Cussans, H. Flacher, J. Goldstein, M. Grimes, G.P. Heath, H.F. Heath, J. Jacob, L. Kreczko, C. Lucas, D.M. Newbold63, S. Paramesvaran, A. Poll, T. Sakuma, S. Seif El Nasr-storey, D. Smith, V.J. Smith Rutherford Appleton Laboratory, Didcot, United Kingdom K.W. Bell, A. Belyaev64, C. Brew, R.M. Brown, L. Calligaris, D. Cieri, D.J.A. Cockerill, J.A. Coughlan, K. Harder, S. Harper, E. Olaiya, D. Petyt, C.H. Shepherd-Themistocleous, A. Thea, I.R. Tomalin, T. Williams Imperial College, London, United Kingdom M. Baber, R. Bainbridge, O. Buchmuller, A. Bundock, D. Burton, S. Casasso, M. Citron, D. Colling, L. Corpe, P. Dauncey, G. Davies, A. De Wit, M. Della Negra, R. Di Maria, P. Dunne, A. Elwood, D. Futyan, Y. Haddad, G. Hall, G. Iles, T. James, R. Lane, C. Laner, R. Lucas63, L. Lyons, A.-M. Magnan, S. Malik, L. Mastrolorenzo, J. Nash, A. Nikitenko48, J. Pela, B. Penning, M. Pesaresi, D.M. Raymond, A. Richards, A. Rose, E. Scott, C. Seez, S. Summers, A. Tapper, K. Uchida, M. Vazquez Acosta65, T. Virdee14, J. Wright, S.C. Zenz Brunel University, Uxbridge, United Kingdom J.E. Cole, P.R. Hobson, A. Khan, P. Kyberd, I.D. Reid, P. Symonds, L. Teodorescu, M. Turner Baylor University, Waco, U.S.A. A. Borzou, K. Call, J. Dittmann, K. Hatakeyama, H. Liu, N. Pastika Catholic University of America, Washington, U.S.A. R. Bartek, A. Dominguez The University of Alabama, Tuscaloosa, U.S.A. A. Buccilli, S.I. Cooper, C. Henderson, P. Rumerio, C. West Boston University, Boston, U.S.A. D. Arcaro, A. Avetisyan, T. Bose, D. Gastler, D. Rankin, C. Richardson, J. Rohlf, L. Sulak, D. Zou R. Syarif Brown University, Providence, U.S.A. G. Benelli, D. Cutts, A. Garabedian, J. Hakala, U. Heintz, J.M. Hogan, O. Jesus, K.H.M. Kwok, E. Laird, G. Landsberg, Z. Mao, M. Narain, S. Piperov, S. Sagir, E. Spencer, University of California, Davis, Davis, U.S.A. R. Breedon, D. Burns, M. Calderon De La Barca Sanchez, S. Chauhan, M. Chertok, J. Conway, R. Conway, P.T. Cox, R. Erbacher, C. Flores, G. Funk, M. Gardner, W. Ko, R. Lander, C. Mclean, M. Mulhearn, D. Pellett, J. Pilot, S. Shalhout, M. Shi, J. Smith, M. Squires, D. Stolp, K. Tos, M. Tripathi University of California, Los Angeles, U.S.A. M. Bachtis, C. Bravo, R. Cousins, A. Dasgupta, A. Florent, J. Hauser, M. Ignatenko, N. Mccoll, D. Saltzberg, C. Schnaible, V. Valuev, M. Weber University of California, Riverside, Riverside, U.S.A. E. Bouvier, K. Burt, R. Clare, J. Ellison, J.W. Gary, S.M.A. Ghiasi Shirazi, G. Hanson, J. Heilman, P. Jandir, E. Kennedy, F. Lacroix, O.R. Long, M. Olmedo Negrete, M.I. Paneva, A. Shrinivas, W. Si, H. Wei, S. Wimpenny, B. R. Yates University of California, San Diego, La Jolla, U.S.A. J.G. Branson, G.B. Cerati, S. Cittolin, M. Derdzinski, R. Gerosa, A. Holzner, D. Klein, V. Krutelyov, J. Letts, I. Macneill, D. Olivito, S. Padhi, M. Pieri, M. Sani, V. Sharma, S. Simon, M. Tadel, A. Vartak, S. Wasserbaech66, C. Welke, J. Wood, F. Wurthwein, A. Yagil, G. Zevi Della Porta bara, U.S.A. N. Amin, R. Bhandari, J. Bradmiller-Feld, C. Campagnari, A. Dishaw, V. Dutta, M. Franco Sevilla, C. George, F. Golf, L. Gouskos, J. Gran, R. Heller, J. Incandela, S.D. Mullin, A. Ovcharova, H. Qu, J. Richman, D. Stuart, I. Suarez, J. Yoo California Institute of Technology, Pasadena, U.S.A. D. Anderson, J. Bendavid, A. Bornheim, J. Bunn, J. Duarte, J.M. Lawhorn, A. Mott, H.B. Newman, C. Pena, M. Spiropulu, J.R. Vlimant, S. Xie, R.Y. Zhu Carnegie Mellon University, Pittsburgh, U.S.A. M.B. Andrews, T. Ferguson, M. Paulini, J. Russ, M. Sun, H. Vogel, I. Vorobiev, M. WeinUniversity of Colorado Boulder, Boulder, U.S.A. J.P. Cumalat, W.T. Ford, F. Jensen, A. Johnson, M. Krohn, S. Leontsinis, T. Mulholland, K. Stenson, S.R. Wagner Cornell University, Ithaca, U.S.A. J. Thom, J. Tucker, P. Wittich, M. Zientek Fair eld University, Fair eld, U.S.A. D. Winn J. Alexander, J. Chaves, J. Chu, S. Dittmer, K. Mcdermott, N. Mirman, G. Nicolas Kaufman, J.R. Patterson, A. Rinkevicius, A. Ryd, L. Skinnari, L. So , S.M. Tan, Z. Tao, Fermi National Accelerator Laboratory, Batavia, U.S.A. S. Abdullin, M. Albrow, G. Apollinari, A. Apresyan, S. Banerjee, L.A.T. Bauerdick, A. Beretvas, J. Berryhill, P.C. Bhat, G. Bolla, K. Burkett, J.N. Butler, H.W.K. Cheung, F. Chlebana, S. Cihangiry, M. Cremonesi, V.D. Elvira, I. Fisk, J. Freeman, E. Gottschalk, L. Gray, D. Green, S. Grunendahl, O. Gutsche, D. Hare, R.M. Harris, S. Hasegawa, J. Hirschauer, Z. Hu, B. Jayatilaka, S. Jindariani, M. Johnson, U. Joshi, B. Klima, B. Kreis, S. Lammel, J. Linacre, D. Lincoln, R. Lipton, M. Liu, T. Liu, R. Lopes De Sa, J. Lykken, K. Maeshima, N. Magini, J.M. Marra no, S. Maruyama, D. Mason, P. McBride, P. Merkel, S. Mrenna, S. Nahn, V. O'Dell, K. Pedro, O. Prokofyev, G. Rakness, L. Ristori, E. SextonKennedy, A. Soha, W.J. Spalding, L. Spiegel, S. Stoynev, J. Strait, N. Strobbe, L. Taylor, S. Tkaczyk, N.V. Tran, L. Uplegger, E.W. Vaandering, C. Vernieri, M. Verzocchi, R. Vidal, M. Wang, H.A. Weber, A. Whitbeck, Y. Wu University of Florida, Gainesville, U.S.A. D. Acosta, P. Avery, P. Bortignon, D. Bourilkov, A. Brinkerho , A. Carnes, M. Carver, D. Curry, S. Das, R.D. Field, I.K. Furic, J. Konigsberg, A. Korytov, J.F. Low, P. Ma, K. Matchev, H. Mei, G. Mitselmakher, D. Rank, L. Shchutska, D. Sperka, L. Thomas, J. Wang, S. Wang, J. Yelton Florida International University, Miami, U.S.A. S. Linn, P. Markowitz, G. Martinez, J.L. Rodriguez Florida State University, Tallahassee, U.S.A. A. Ackert, T. Adams, A. Askew, S. Bein, S. Hagopian, V. Hagopian, K.F. Johnson, T. Kolberg, H. Prosper, A. Santra, R. Yohay Florida Institute of Technology, Melbourne, U.S.A. M.M. Baarmand, V. Bhopatkar, S. Colafranceschi, M. Hohlmann, D. Noonan, T. Roy, F. Yumiceva University of Illinois at Chicago (UIC), Chicago, U.S.A. M.R. Adams, L. Apanasevich, D. Berry, R.R. Betts, I. Bucinskaite, R. Cavanaugh, O. Evdokimov, L. Gauthier, C.E. Gerber, D.J. Hofman, K. Jung, I.D. Sandoval Gonzalez, N. Varelas, H. Wang, Z. Wu, M. Zakaria, J. Zhang The University of Iowa, Iowa City, U.S.A. B. Bilki67, W. Clarida, K. Dilsiz, S. Durgut, R.P. Gandrajula, M. Haytmyradov, V. Khristenko, J.-P. Merlo, H. Mermerkaya68, A. Mestvirishvili, A. Moeller, J. Nachtman, H. Ogul, Y. Onel, F. Ozok69, A. Penzo, C. Snyder, E. Tiras, J. Wetzel, K. Yi Johns Hopkins University, Baltimore, U.S.A. B. Blumenfeld, A. Cocoros, N. Eminizer, D. Fehling, L. Feng, A.V. Gritsan, P. Maksimovic, J. Roskes, U. Sarica, M. Swartz, M. Xiao, C. You The University of Kansas, Lawrence, U.S.A. A. Al-bataineh, P. Baringer, A. Bean, S. Boren, J. Bowen, J. Castle, L. Forthomme, R.P. Kenny III, S. Khalil, A. Kropivnitskaya, D. Majumder, W. Mcbrayer, M. Murray, S. Sanders, R. Stringer, J.D. Tapia Takaki, Q. Wang Kansas State University, Manhattan, U.S.A. A. Ivanov, K. Kaadze, Y. Maravin, A. Mohammadi, L.K. Saini, N. Skhirtladze, S. Toda Lawrence Livermore National Laboratory, Livermore, U.S.A. F. Rebassoo, D. Wright University of Maryland, College Park, U.S.A. C. Anelli, A. Baden, O. Baron, A. Belloni, B. Calvert, S.C. Eno, C. Ferraioli, J.A. Gomez, N.J. Hadley, S. Jabeen, G.Y. Jeng, R.G. Kellogg, J. Kunkle, A.C. Mignerey, F. Ricci-Tam, Y.H. Shin, A. Skuja, M.B. Tonjes, S.C. Tonwar Massachusetts Institute of Technology, Cambridge, U.S.A. D. Abercrombie, B. Allen, A. Apyan, V. Azzolini, R. Barbieri, A. Baty, R. Bi, K. Bierwagen, S. Brandt, W. Busza, I.A. Cali, M. D'Alfonso, Z. Demiragli, G. Gomez Ceballos, M. Goncharov, D. Hsu, Y. Iiyama, G.M. Innocenti, M. Klute, D. Kovalskyi, K. Krajczar, Y.S. Lai, Y.-J. Lee, A. Levin, P.D. Luckey, B. Maier, A.C. Marini, C. Mcginn, C. Mironov, S. Narayanan, X. Niu, C. Paus, C. Roland, G. Roland, J. Salfeld-Nebgen, G.S.F. Stephans, K. Tatar, D. Velicanu, J. Wang, T.W. Wang, B. Wyslouch University of Minnesota, Minneapolis, U.S.A. A.C. Benvenuti, R.M. Chatterjee, A. Evans, P. Hansen, S. Kalafut, S.C. Kao, Y. Kubota, Z. Lesko, J. Mans, S. Nourbakhsh, N. Ruckstuhl, R. Rusack, N. Tambe, J. Turkewitz University of Mississippi, Oxford, U.S.A. J.G. Acosta, S. Oliveros University of Nebraska-Lincoln, Lincoln, U.S.A. E. Avdeeva, K. Bloom, D.R. Claes, C. Fangmeier, R. Gonzalez Suarez, R. Kamalieddin, I. Kravchenko, A. Malta Rodrigues, J. Monroy, J.E. Siado, G.R. Snow, B. Stieger State University of New York at Bu alo, Bu alo, U.S.A. M. Alyari, J. Dolen, A. Godshalk, C. Harrington, I. Iashvili, J. Kaisen, D. Nguyen, A. Parker, S. Rappoccio, B. Roozbahani Northeastern University, Boston, U.S.A. G. Alverson, E. Barberis, A. Hortiangtham, A. Massironi, D.M. Morse, D. Nash, T. Orimoto, R. Teixeira De Lima, D. Trocino, R.-J. Wang, D. Wood Northwestern University, Evanston, U.S.A. S. Bhattacharya, O. Charaf, K.A. Hahn, A. Kumar, N. Mucia, N. Odell, B. Pollack, M.H. Schmitt, K. Sung, M. Trovato, M. Velasco University of Notre Dame, Notre Dame, U.S.A. N. Dev, M. Hildreth, K. Hurtado Anampa, C. Jessop, D.J. Karmgard, N. Kellams, K. Lannon, N. Marinelli, F. Meng, C. Mueller, Y. Musienko35, M. Planer, A. Reinsvold, R. Ruchti, N. Rupprecht, G. Smith, S. Taroni, M. Wayne, M. Wolf, A. Woodard The Ohio State University, Columbus, U.S.A. J. Alimena, L. Antonelli, B. Bylsma, L.S. Durkin, S. Flowers, B. Francis, A. Hart, C. Hill, R. Hughes, W. Ji, B. Liu, W. Luo, D. Puigh, B.L. Winer, H.W. Wulsin Princeton University, Princeton, U.S.A. S. Cooperstein, O. Driga, P. Elmer, J. Hardenbrook, P. Hebda, D. Lange, J. Luo, D. Marlow, T. Medvedeva, K. Mei, I. Ojalvo, J. Olsen, C. Palmer, P. Piroue, D. Stickland, A. Svyatkovskiy, C. Tully University of Puerto Rico, Mayaguez, U.S.A. S. Malik Purdue University, West Lafayette, U.S.A. A. Barker, V.E. Barnes, S. Folgueras, L. Gutay, M.K. Jha, M. Jones, A.W. Jung, A. Khatiwada, D.H. Miller, N. Neumeister, J.F. Schulte, X. Shi, J. Sun, F. Wang, W. Xie Purdue University Northwest, Hammond, U.S.A. N. Parashar, J. Stupak Rice University, Houston, U.S.A. A. Adair, B. Akgun, Z. Chen, K.M. Ecklund, F.J.M. Geurts, M. Guilbaud, W. Li, B. Michlin, M. Northup, B.P. Padley, J. Roberts, J. Rorie, Z. Tu, J. Zabel University of Rochester, Rochester, U.S.A. B. Betchart, A. Bodek, P. de Barbaro, R. Demina, Y.t. Duh, T. Ferbel, M. Galanti, A. Garcia-Bellido, J. Han, O. Hindrichs, A. Khukhunaishvili, K.H. Lo, P. Tan, M. Verzetti Rutgers, The State University of New Jersey, Piscataway, U.S.A. A. Agapitos, J.P. Chou, Y. Gershtein, T.A. Gomez Espinosa, E. Halkiadakis, M. Heindl, E. Hughes, S. Kaplan, R. Kunnawalkam Elayavalli, S. Kyriacou, A. Lath, K. Nash, M. Osherson, H. Saka, S. Salur, S. Schnetzer, D. She eld, S. Somalwar, R. Stone, S. Thomas, P. Thomassen, M. Walker University of Tennessee, Knoxville, U.S.A. A.G. Delannoy, M. Foerster, J. Heideman, G. Riley, K. Rose, S. Spanier, K. Thapa Texas A&M University, College Station, U.S.A. O. Bouhali70, A. Celik, M. Dalchenko, M. De Mattia, A. Delgado, S. Dildick, R. Eusebi, J. Gilmore, T. Huang, E. Juska, T. Kamon71, R. Mueller, Y. Pakhotin, R. Patel, A. Perlo , L. Pernie, D. Rathjens, A. Safonov, A. Tatarinov, K.A. Ulmer Texas Tech University, Lubbock, U.S.A. N. Akchurin, J. Damgov, F. De Guio, C. Dragoiu, P.R. Dudero, J. Faulkner, E. Gurpinar, S. Kunori, K. Lamichhane, S.W. Lee, T. Libeiro, T. Peltola, S. Undleeb, I. Volobouev, Z. Wang Vanderbilt University, Nashville, U.S.A. S. Tuo, J. Velkovska, Q. Xu University of Virginia, Charlottesville, U.S.A. T. Sinthuprasith, X. Sun, Y. Wang, E. Wolfe, F. Xia Wayne State University, Detroit, U.S.A. C. Clarke, R. Harr, P.E. Karchin, J. Sturdy S. Greene, A. Gurrola, R. Janjam, W. Johns, C. Maguire, A. Melo, H. Ni, P. Sheldon, M.W. Arenton, P. Barria, B. Cox, J. Goodell, R. Hirosky, A. Ledovskoy, H. Li, C. Neu, University of Wisconsin - Madison, Madison, WI, U.S.A. D.A. Belknap, J. Buchanan, C. Caillol, S. Dasu, L. Dodd, S. Duric, B. Gomber, M. Grothe, M. Herndon, A. Herve, P. Klabbers, A. Lanaro, A. Levine, K. Long, R. Loveless, T. Perry, G.A. Pierro, G. Polese, T. Ruggles, A. Savin, N. Smith, W.H. Smith, D. Taylor, N. Woods y: Deceased China 1: Also at Vienna University of Technology, Vienna, Austria 2: Also at State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, 3: Also at Institut Pluridisciplinaire Hubert Curien (IPHC), Universite de Strasbourg, CNRS/IN2P3, Strasbourg, France 4: Also at Universidade Estadual de Campinas, Campinas, Brazil 5: Also at Universidade Federal de Pelotas, Pelotas, Brazil 6: Also at Universite Libre de Bruxelles, Bruxelles, Belgium 7: Also at Deutsches Elektronen-Synchrotron, Hamburg, Germany 8: Also at Joint Institute for Nuclear Research, Dubna, Russia 9: Now at Ain Shams University, Cairo, Egypt 10: Now at British University in Egypt, Cairo, Egypt Moscow, Russia 12: Also at Universite de Haute Alsace, Mulhouse, France 13: Also at Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 14: Also at CERN, European Organization for Nuclear Research, Geneva, Switzerland 15: Also at RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany 16: Also at University of Hamburg, Hamburg, Germany 17: Also at Brandenburg University of Technology, Cottbus, Germany 18: Also at Institute of Nuclear Research ATOMKI, Debrecen, Hungary 19: Also at MTA-ELTE Lendulet CMS Particle and Nuclear Physics Group, Eotvos Lorand University, Budapest, Hungary 20: Also at Institute of Physics, University of Debrecen, Debrecen, Hungary 21: Also at Indian Institute of Technology Bhubaneswar, Bhubaneswar, India 22: Also at University of Visva-Bharati, Santiniketan, India 23: Also at Indian Institute of Science Education and Research, Bhopal, India 24: Also at Institute of Physics, Bhubaneswar, India 25: Also at University of Ruhuna, Matara, Sri Lanka 26: Also at Isfahan University of Technology, Isfahan, Iran 27: Also at Yazd University, Yazd, Iran 28: Also at Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran 29: Also at Universita degli Studi di Siena, Siena, Italy 30: Also at Purdue University, West Lafayette, U.S.A. 31: Also at International Islamic University of Malaysia, Kuala Lumpur, Malaysia 32: Also at Malaysian Nuclear Agency, MOSTI, Kajang, Malaysia 33: Also at Consejo Nacional de Ciencia y Tecnolog a, Mexico city, Mexico 34: Also at Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland 35: Also at Institute for Nuclear Research, Moscow, Russia 36: Now at National Research Nuclear University 'Moscow 37: Also at St. Petersburg State Polytechnical University, St. Petersburg, Russia 38: Also at University of Florida, Gainesville, U.S.A. 39: Also at P.N. Lebedev Physical Institute, Moscow, Russia 40: Also at California Institute of Technology, Pasadena, U.S.A. 41: Also at Budker Institute of Nuclear Physics, Novosibirsk, Russia 42: Also at Faculty of Physics, University of Belgrade, Belgrade, Serbia 43: Also at INFN Sezione di Roma; Sapienza Universita di Roma, Rome, Italy Belgrade, Serbia 45: Also at Scuola Normale e Sezione dell'INFN, Pisa, Italy 46: Also at National and Kapodistrian University of Athens, Athens, Greece 47: Also at Riga Technical University, Riga, Latvia 48: Also at Institute for Theoretical and Experimental Physics, Moscow, Russia 49: Also at Albert Einstein Center for Fundamental Physics, Bern, Switzerland 50: Also at Adiyaman University, Adiyaman, Turkey 51: Also at Istanbul Aydin University, Istanbul, Turkey 52: Also at Mersin University, Mersin, Turkey 53: Also at Cag University, Mersin, Turkey 44: Also at University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, 55: Also at Gaziosmanpasa University, Tokat, Turkey 56: Also at Ozyegin University, Istanbul, Turkey 57: Also at Izmir Institute of Technology, Izmir, Turkey 58: Also at Marmara University, Istanbul, Turkey 59: Also at Kafkas University, Kars, Turkey 60: Also at Istanbul Bilgi University, Istanbul, Turkey 61: Also at Yildiz Technical University, Istanbul, Turkey 62: Also at Hacettepe University, Ankara, Turkey 63: Also at Rutherford Appleton Laboratory, Didcot, United Kingdom 64: Also at School of Physics and Astronomy, University of Southampton, Southampton, United 65: Also at Instituto de Astrof sica de Canarias, La Laguna, Spain 66: Also at Utah Valley University, Orem, U.S.A. 67: Also at Argonne National Laboratory, Argonne, U.S.A. 68: Also at Erzincan University, Erzincan, Turkey 69: Also at Mimar Sinan University, Istanbul, Istanbul, Turkey 70: Also at Texas A&M University at Qatar, Doha, Qatar 71: Also at Kyungpook National University, Daegu, Korea [1] T. Han , The `top priority' at the LHC, Int . J. Mod. Phys. A 23 ( 2008 ) 4107 [2] W. Bernreuther , Top quark physics at the LHC, J. Phys. G 35 ( 2008 ) 083001 [3] A. Buckley et al., Constraining top quark e ective theory in the LHC Run II era , JHEP 04 [4] U. Baur , A. Juste , L.H. Orr and D. Rainwater , Probing electroweak top quark couplings at hadron colliders , Phys. Rev. D 71 ( 2005 ) 054013 [ hep -ph/0412021] [INSPIRE]. [5] A.O. Bouzas and F. Larios , Electromagnetic dipole moments of the top quark , Phys. Rev . D [11] D. Peng-Fei et al., QCD corrections to associated production of tt at hadron colliders , [13] CMS collaboration , The CMS experiment at the CERN LHC , 2008 JINST 3 S08004 [14] J. Alwall et al., The automated computation of tree-level and next-to-leading order [28] N. Kidonakis, NNLL resummation for s-channel single top quark production , Phys. Rev . D [33] M. Cacciari , G.P. Salam and G. Soyez, The anti-kt jet clustering algorithm , JHEP 04 ( 2008 ) [34] M. 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