Search for anomaly-mediated supersymmetry breaking with the ATLAS detector based on a disappearing-track signature in pp collisions at \(\sqrt{s} = 7~\mathrm{TeV}\)

The European Physical Journal C, Apr 2012

In models of anomaly-mediated supersymmetry breaking (AMSB), the lightest chargino is predicted to have a lifetime long enough to be detected in collider experiments. This letter explores AMSB scenarios in pp collisions at \(\sqrt {s}=7\ \mathrm{TeV}\) by attempting to identify decaying charginos which result in tracks that appear to have few associated hits in the outer region of the tracking system. The search was based on data corresponding to an integrated luminosity of 1.02 fb−1 collected with the ATLAS detector in 2011. The p T spectrum of candidate tracks is found to be consistent with the expectation from Standard Model background processes and constraints on the lifetime and the production cross section were obtained. In the minimal AMSB framework with m 3/2<32 TeV, m 0<1.5 TeV, tanβ=5 and μ>0, a chargino having mass below 92 GeV and a lifetime between 0.5 ns and 2 ns is excluded at 95 % confidence level.

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Search for anomaly-mediated supersymmetry breaking with the ATLAS detector based on a disappearing-track signature in pp collisions at \(\sqrt{s} = 7~\mathrm{TeV}\)

The ATLAS Collaboration 0 0 CERN, 1211 Geneva 23, Switzerland In models of anomaly-mediated supersymmetry breaking (AMSB), the lightest chargino is predicted to have a lifetime long enough to be detected in collider experiments. This letter explores AMSB scenarios in pp collisions at s = 7 TeV by attempting to identify decaying charginos which result in tracks that appear to have few associated hits in the outer region of the tracking system. The search was based on data corresponding to an integrated luminosity of 1.02 fb1 collected with the ATLAS detector in 2011. The pT spectrum of candidate tracks is found to be consistent with the expectation from Standard Model background processes and constraints on the lifetime and the production cross section were obtained. In the minimal AMSB framework with m3/2 < 32 TeV, m0 < 1.5 TeV, tan = 5 and > 0, a chargino having mass below 92 GeV and a lifetime between 0.5 ns and 2 ns is excluded at 95 % confidence level. - Supersymmetry (SUSY) [19] is a promising solution to the hierarchy problem of the Standard Model (SM) and the search for SUSY is an important programme at the Large Hadron Collider (LHC). For each SM particle, SUSY postulates a supersymmetric partner with identical quantum numbers but with a spin that differs by 1/2. Since scalar superpartners of quarks and leptons with masses equal to quarks and leptons have not been observed in previous searches, SUSY must be a broken symmetry. One mechanism which provides a calculable mass spectrum of supersymmetric particles is provided by anomaly mediation [10, 11]. The anomaly-mediated SUSY breaking (AMSB) model provides a constrained particle mass spectrum; the ratios of the three gaugino masses are given approximately as M1 : M2 : M3 3 : 1 : 7 where Mi (i = 1, 2, 3) are the bino, wino and gluino masses, respectively. The neutral wino becomes the lightest supersymmetric particle (LSP) while the charged wino becomes slightly heavier due to radiative corrections involving electroweak gauge bosons in the loops. This phenomenological feature of the nearly degenerate lightest chargino (1) and neutralino (10) has the important implication that predominantly decays into 10 plus a low-momentum 1 (100 MeV) . The decay length of 1 is typically expected to be a few centimeters at LHC energies; some 1 charginos could therefore decay inside the tracking volume of the ATLAS detector. The 10 escapes detection and the softly emitted is not reconstructed. A track arising from a 1 with these characteristics is classified as a disappearing track. The search described in this letter is based on this signature of decaying charginos which leads to a track having few associated hits in the outer part of the tracking volume. 2 The ATLAS detector ATLAS is a multi-purpose detector [12], covering nearly the entire solid angle1 around the collision point with layers of inner tracking devices surrounded by a superconducting solenoid providing a 2 T magnetic field, a calorimeter system and a muon spectrometer. The inner tracking detector provides tracking in the region || < 2.5. It consists of pixel and silicon microstrip (SCT) detectors inside a transition radiation tracker (TRT). 1ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point (IP) in the centre of the detector and the zaxis coinciding with the axis of the beam pipe. The x-axis points from the IP to the centre of the LHC ring, and the y-axis points upward. Cylindrical coordinates (r, ) are used in the transverse plane, being the azimuthal angle around the beam pipe. The pseudorapidity is defined in terms of the polar angle as = ln tan(/2). Of particular importance to this analysis is the TRT which covers the region || < 2.0. The barrel TRT is divided into inner, middle and outer concentric rings of 32 modules comprising a stack in the azimuthal angle; each covers the radial range from 563 mm to 1066 mm and || < 1.0. A module consists of a carbon-fibre laminate shell and an array of straw tubes and has a different structure for each ring. The calorimeter system covers the range || < 4.9. The electromagnetic calorimeter is a lead/liquid-argon (LAr) detector in the barrel (|| < 1.475) and endcap (1.375 < || < 3.2) regions. The hadron calorimeters are composed of a steel and scintillator barrel (|| < 1.7), a LAr/copper endcap (1.5 < || < 3.2) and a LAr forward system (3.1 < || < 4.9) with copper and tungsten absorbers. The muon spectrometer consists of three large superconducting toroids with 24 coils, a system of trigger chambers and precision tracking chambers which provide muon momentum measurements up to || of 2.7. 3 Simulated event samples Table 1 Summary of AMSB signal parameters, chargino masses and their NLO cross sections with tan = 5 and sgn() = +1 In the model, gluinos and squarks are expected to be produced copiously via the strong interaction in pp collisions. The decay cascade of these to the 1 and 10 produces multiple jets with high transverse momentum (pT). LSPs escape from the detector, resulting in an event topology with multiple jets and large missing transverse momentum (ETmiss). Chargino tracks are expected to have significant transverse momentum since the difference between the gluino and chargino masses is large; the chargino track typically has pT > 50 GeV and is well isolated from the jet activity in the event. 4 Data and event selection The analysis was based on pp collision data at s = 7 TeV recorded from March to July 2011. The corresponding integrated luminosity, after the application of beam, detector and data quality requirements, was 1.02 fb1. Events were selected at the trigger level by requiring at least one jet with a transverse momentum, measured at the electromagnetic scale, above 75 GeV, and a missing transverse momentum above 55 GeV. Jets were reconstructed using the anti-kt algorithm [23] with a distance parameter of 0.4. The inputs to the jet reconstruction algorithm were three-dimensional topological calorimeter energy clusters [24]. The measurement of jet transverse momentum at the electromagnetic scale (pTjet,EM) underestimates the true momentum due to the nature of the non-compensating calorimeters and the dead material. Thus, an average correction [25], depending on and pjet,EM, was applied to obtain the calibrated jet pT. Jets T with pT > 20 GeV and || < 3.2 were selected. Electron candidates were selected with medium purity cuts, as described in Ref. [26]. Furthermore, electrons were required to fulfill the requirements of pT > 10 GeV, || < 2.47 and R< 0.2 pTtrack/pT < 0.1, where R< 0.2 pTtrack is the sum of pT for all the tracks with pT > 1 GeV in a cone of R ( ) 2 + ( ) 2 < 0.2 around the electron candidate, excluding the pT of the electron candidate itself. Muon candidates were identified by an algorithm which combines a track reconstructed in the muon spectrometer with a track in the inner detector. Furthermore, muons were required to have pT > 10 GeV and || < 2.7, and to be isolated [27]: the sum of pT of tracks within a cone of R < 0.2 around the muon candidate (excluding the muon candidate itself) was required to be less than 1.8 GeV. Following the object reconstruction described above, overlaps between jets and leptons were resolved. First, any jet candidate lying within a distance of R < 0.2 of an electron was discarded. Then, any lepton candidates within a distance of R < 0.4 of any surviving jet were discarded. The calculation of ETmiss was based on the transverse momenta of jets and lepton candidates, and all clusters in the calorimeter that are not associated to such objects [28]. In order to suppress non-collision background events, additional selection criteria [25] were applied to jets. Signal candidate events were required to have no electron or muon candidates (lepton veto), ETmiss > 130 GeV and three leading (highest pT) jets with pT > 130 GeV for one jet and pT > 60 GeV for another two jets (kinematic selection). The trigger selection is fully efficient for signal events satisfying the kinematic selection requirements. The search described in this letter was based on the detection of charginos decaying in the TRT. The average number of hits on a track going through the TRT in the central region is about 34 and consecutive hits can be observed along the track with small radial spacing between adjacent hits. This feature provides the capability of substantial discrimination between penetrating and decaying charged particles. If a chargino decays in the volume of the inner or middle TRT modules, multiple hits associated to the chargino track are expected in the SCT detector but not in the outer TRT subdetector. Such a chargino track candidate can be fully reconstructed by the ATLAS standard track reconstruction algorithm. The chargino candidate tracks were required to fulfill the following criteria: (1) The track should have at least one hit in the innermost layer of the pixel detector. (2) The track should have at least six hits in the SCT. (3) The track should have |d0| < 1.5 mm and |z0 sin | < 1.5 mm, where d0 and z0 are the transverse and longitudinal impact parameters. (4) There should be no other tracks with pT > 0.5 GeV within a cone of radius R = 0.05. (5) The candidate track should have the highest pT among the isolated tracks in the event and have pT above 10 GeV. (6) The track should point to the TRT barrel layers and not point to the inactive regions around = 0. (7) The number of hits in the TRT outer module associated to the track (NToRutTer) should be fewer than five. The first four criteria were applied to all tracks in the event in order to ensure a well-reconstructed primary track whereas Fig. 1 The NToRutTer distribution for data and signal events (LL01, = 1 ns) with the high-pT isolated track selection. The selection 1 boundary is indicated by the arrow. The expectation from SM MC events, normalized to the number of observed events, is also shown. When charginos decay before reaching the TRT outer module, NToRutTer is expected to have a value near zero; conversely, SM charged particles traversing the TRT typically have NToRutTer 15 the fifth is meant to select chargino tracks that usually have the highest pT in the event. The chargino tracks sufficiently fulfill the fifth criterion. The sixth criterion was based on the extrapolated track position, and was set to avoid inactive regions of the TRT. This requirement helped to reject fake disappearing tracks and works as an effective acceptance cut of || < 0.63. For the seventh criterion, NToRutTer was calculated by counting TRT hits lying on the extrapolated track. The hits satisfying d < rstraw were taken into account, where d is the distance between the hit and the track in the transverse plane and rstraw is the radius of the straw tube. Hereafter, unless explicitly stated otherwise, highpT isolated track selection and disappearing track selection indicate criteria (1)(6) and (1)(7), respectively. Figure 1 shows the NToRutTer distributions with the high-pT isolated track selection requirements for data, signal and SM MC events. When charginos decay before reaching the TRT outer module, NToRutTer is expected to have a value near zero; conversely, SM charged particles traversing the TRT typically have NToRutTer 15. The sample of selected tracks after requirements (1)(6) is dominated by through-going tracks with NToRutTer 15. Criterion (7) removes the vast majority of these tracks: although it reduces the signal efficiency, it enhances the expected signal to background ratio very strongly. These criteria select charginos decaying in the region 514 < r < 863 mm effectively. The data reduction is summarized in Table 2. After the application of all kinematic and track selection criteria, 185 candidate events remained. 5 Background estimation With the selection criteria described above, there are two main background sources for high-pT disappearing tracks: Charged hadrons (mostly charged pions) interacting with material in the TRT detector. Low-pT charged particles whose pT is badly measured due to scattering in the inner detector material. The two categories are labelled as high-pT interacting hadron track and bad track backgrounds, respectively. Figure 2 shows schematically the origins of disappearing high-pT tracks. According to the MC simulation, high-pT interacting hadron tracks were responsible for more than 95 % of the background tracks. Electrons having low pT can be classified as disappearing tracks due to bremsstrahlung, however, the contribution of these tracks was negligibly small after the lepton veto and the track selection criterion (5). The fraction of events containing these background tracks is expected to be 104; background estimation based on the MC simulation would therefore suffer from large uncertainties due to the lack of sufficient MC statistics and also from the difficulty in simulating the properties of these background mechanisms. A data-driven background estimation technique was therefore used to estimate the background track pT spectrum, which used control samples enriched in the two background categories. The main contribution to the high-pT interacting hadron background originated from charged hadrons in jets and hadronic decays. In the pT range above 10 GeV, where inelastic interactions dominate, the interaction rate has nearly no pTdependence [29]. Therefore, the pT spectrum of interacting hadron tracks was obtained from that of non-interacting hadron tracks. By adopting the same kinematic selection criteria as those for the signal and ensuring penetration through the TRT detector by requiring NToRutTer > 10, a pure sample of high-pT non-interacting hadron tracks was obtained. The contamination from bad tracks and any chargino signal was removed by requiring the calorimeter activity associated to the track, R< 0.1 ETclus/pTtrack, to be larger than 0.3, where pTtrack is the pT of the track and R< 0.1 ETclus is the Fig. 2 Origins of disappearing high-pT tracks sum of cluster transverse energies in a cone of R = 0.1 around the track. Simulation studies indicated that the pT spectrum of bad tracks depends little on the production process. A sample with an enhanced bad track contribution was therefore obtained with the same track quality requirements as for the chargino track, but requiring ETmiss < 100 GeV. The ETmiss requirement makes this sample orthogonal to the signal search sample. In addition, the number of pixel hits associated to the track was required to be zero, and R< 0.1 ETclus/ptrack < 0.3 in order to reject possible con T tributions from high-pT interacting hadron tracks and to enhance the purity of bad tracks. The requirement on the number of pixel hits had negligible impact on the shape of the reconstructed pT spectrum. The purity of bad tracks was close to 100 % after these requirements. An ansatz functional form (1 + x)a0 /xa1+a2 ln(x) was fitted to the pT spectrum of the control sample of the highpT non-interacting hadron tracks, where x ptrack and ai T (i = 0, 1, 2) are fit parameters. Figure 3(a) shows the track pT distribution and the shape derived from a maximum likelihood fit. Alternative fit functions gave shapes that agreed with each other and with the original form within the fit uncertainties. The choice of functional form in this analysis was based on the 2 values. Bad tracks could have anomalously high values of pT and become a significant background. Therefore, for the bad track background shape, a flat term representing the high-pT tail was added to give an estimate in the region of interest. Fig. 3 The pT distributions of high-pT hadron track (a) and bad track (b) background control samples. The data and the fitted model are shown by the solid circles and the line, respectively. The significance The resulting functional form was (1 + x)b0 /xb1+b2 ln(x) + b3, where bi (i = 0, 1, 2, 3) are fit parameters. The shape of the bad track background is shown in Fig. 3(b). 6 Signal extraction and constraints In order to evaluate how well the observed data agree with a given signal model, a statistical test was performed based on a maximum likelihood. The likelihood function for the sample of observed events (nobs), using the track pT, is defined as: exp where s, ns , nb and fbad are the signal strength (i.e. the ratio of a given cross section to its predicted value), the expected number of signal events for a given model, the number of background events and the fraction of bad tracks in the background, respectively. The parameters s, nb and fbad were left free in the fit. The probability density functions of signal, interacting hadron track and bad track, Ls, Lhad and Lbad, are shown in Fig. 4. The full shape of the distributions for pT > 10 GeV was fitted with the two background contributions, and a signal contribution was also included in the fit for pT > 50 GeV. A small signal contribution below pT = 50 GeV was neglected. The effects of systematic uncertainties were incorporated via constraint terms on Fig. 4 Probability densities of the signal (LL01, 1 = 1 ns) and background components, shown as a function of track pT. In the signal case, only the region pT > 50 GeV is shown nuisance parameters. The overall normalisation of the signal and the parameters describing the background track pT shapes were set as nuisance parameters; they were treated with a normal distribution and multivariate normal distributions with covariance matrices obtained by the fit of the background control samples, respectively. A total uncertainty of 25 % was found for the signal normalisation; the main contribution comes from the uncertainties in the theoretical cross section from the renormalisation and factorisation scales (18 %) and the parton distribution functions (9 %). The jet energy scale [25], the track reconstruction efficiency [30] and the integrated luminosity [31, 32] could alter the signal yield; their contributions were estimated to be 9 %, 2 % and 3.7 %, respectively. The systematic uncertainties due to pile-up were evaluated by examining the stability of the signal acceptance and the pT spectra of background tracks as a function of the number of pp interactions. Both data and signal MC were used for this purpose, and the resulting uncertainties were found to be negligible. Figure 5 shows the best-fit shape of the signal + background model for the sample signal point LL01 with 1 = 1 ns (nsexp = 4.2). The fit resulted in nb = 185 14 and the best fit values of s and fbad were zero; upper limits of s < 0.15 and fbad < 4.0 102 were set at 68 % CL. The p-value for the consistency of the observed data with the background-only hypothesis was calculated to be 0.5, showing that the observed track pT spectrum was in agreement with the background expectation. The result also indicated that interacting hadron tracks were the dominant background, consistent with MC predictions. The expected background and observed events in the region pT > 50 GeV were 13 1 and 5, respectively; this background estimate was derived from the background-only fit in the region 10 < pT 50 GeV. Model-independent upper limits were set on the cross section times acceptance for non-SM processes with the final state satisfying the kinematic and track selection criteria. Figure 6 shows 95 % CL upper limits on the cross section times acceptance for candidate tracks with pT > pT0 as a function of pT0. The 95 % CL upper limit on the cross section for a given model was set by the point where the CL of the signal + background hypothesis based on the profile likelihood ratio [33] and Fig. 6 Model-independent upper limits on the cross section ( ) times acceptance (A) for a non-SM physics process containing an isolated, disappearing track with pT > pT0 as a function of pT0. The observed and expected bounds at 95 % CL are shown Fig. 7 The observed and expected 95 % CL upper limits on the signal cross section as a function of chargino lifetime for m1 = 90.2 GeV. The band and the dotted line indicate the range in which the limit is expected to lie due to the fluctuations in the expected background the CLs method [34, 35] falls below 5 % when scanning the CL along various values of s. Figure 7 shows the observed limit on the signal cross section at 95 % CL as a function of for the signal model LL01. Limits on the 1 chargino lifetime were also set: < 0.2 or > 4 ns for 1 1 a chargino with a mass of 90 GeV. Moreover, a constraint on the chargino mass and lifetime was set by the scan of the observed cross section limits for the benchmark models, as shown in Fig. 8. In the framework of minimal AMSB with m3/2 < 32 TeV, m0 < 1.5 TeV, tan = 5 and > 0, a chargino with m < 92 GeV and 0.5 < < 2 ns was 1 1 excluded at 95 % CL. Fig. 8 The constraint on the chargino mass and lifetime in a minimal AMSB model with m3/2 < 32 TeV, m0 < 1.5 TeV, tan = 5 and > 0. The observed and expected bounds at 95 % CL are shown 7 Conclusion The results of a search for long-lived charginos in pp collisions with the ATLAS detector using 1.02 fb1 of data were presented in the context of AMSB scenarios. The analysis used a signature of high-pT isolated tracks with few associated hits in the outer part of the ATLAS tracking system. The pT spectrum of observed candidate tracks was found to be consistent with the expectation from SM background processes. Constraints on the AMSB chargino mass and lifetime were set; a chargino having m < 92 GeV and 0.5 < < 2 ns was excluded at 1 1 95 % CL. Acknowledgements We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET and ERC, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNAS, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW, Poland; GRICES and FCT, Portugal; MERYS (MECTS), Romania; MES of Russia and ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slovakia; ARRS and MVZT, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SER, SNSF and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE and NSF, United States of America. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN and the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA) and in the Tier-2 facilities worldwide. Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited. 22Department of Physics, Brandeis University, Waltham MA, United States of America 23(a)Universidade Federal do Rio De Janeiro COPPE/EE/IF, Rio de Janeiro; (b)Federal University of Juiz de Fora (UFJF), Juiz de Fora; (c)Federal University of Sao Joao del Rei (UFSJ), Sao Joao del Rei; (d)Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo, Brazil 24Physics Department, Brookhaven National Laboratory, Upton NY, United States of America 25(a)National Institute of Physics and Nuclear Engineering, Bucharest; (b)University Politehnica Bucharest, Bucharest; (c)West University in Timisoara, Timisoara, Romania 26Departamento de Fsica, Universidad de Buenos Aires, Buenos Aires, Argentina 27Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 28Department of Physics, Carleton University, Ottawa ON, Canada 29CERN, Geneva, Switzerland 30Enrico Fermi Institute, University of Chicago, Chicago IL, United States of America 31(a)Departamento de Fisica, Pontificia Universidad Catlica de Chile, Santiago; (b)Departamento de Fsica, Universidad Tcnica Federico Santa Mara, Valparaso, Chile 32(a)Institute of High Energy Physics, Chinese Academy of Sciences, Beijing; (b)Department of Modern Physics, University of Science and Technology of China, Anhui; (c)Department of Physics, Nanjing University, Jiangsu; (d)School of Physics, Shandong University, Shandong, China 33Laboratoire de Physique Corpusculaire, Clermont Universit and Universit Blaise Pascal and CNRS/IN2P3, Aubiere Cedex, France 34Nevis Laboratory, Columbia University, Irvington NY, United States of America 35Niels Bohr Institute, University of Copenhagen, Kobenhavn, Denmark 36(a)INFN Gruppo Collegato di Cosenza; (b)Dipartimento di Fisica, Universit della Calabria, Arcavata di Rende, Italy 37Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Krakow, Poland 38The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland 39Physics Department, Southern Methodist University, Dallas TX, United States of America 40Physics Department, University of Texas at Dallas, Richardson TX, United States of America 41DESY, Hamburg and Zeuthen, Germany 42Institut fr Experimentelle Physik IV, Technische Universitt Dortmund, Dortmund, Germany 43Institut fr Kern- und Teilchenphysik, Technical University Dresden, Dresden, Germany 44Department of Physics, Duke University, Durham NC, United States of America 45SUPA - School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 46Fachhochschule Wiener Neustadt, Johannes Gutenbergstrasse 3, 2700 Wiener Neustadt, Austria 47INFN Laboratori Nazionali di Frascati, Frascati, Italy 48Fakultt fr Mathematik und Physik, Albert-Ludwigs-Universitt, Freiburg i.Br., Germany 49Section de Physique, Universit de Genve, Geneva, Switzerland 50(a)INFN Sezione di Genova; (b)Dipartimento di Fisica, Universit di Genova, Genova, Italy 51(a)E.Andronikashvili Institute of Physics, Tbilisi State University, Tbilisi; (b)High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia 52II Physikalisches Institut, Justus-Liebig-Universitt Giessen, Giessen, Germany 53SUPA - School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 54II Physikalisches Institut, Georg-August-Universitt, Gttingen, Germany 55Laboratoire de Physique Subatomique et de Cosmologie, Universit Joseph Fourier and CNRS/IN2P3 and Institut National Polytechnique de Grenoble, Grenoble, France 56Department of Physics, Hampton University, Hampton VA, United States of America 57Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge MA, United States of America 58(a)Kirchhoff-Institut fr Physik, Ruprecht-Karls-Universitt Heidelberg, Heidelberg; (b)Physikalisches Institut, Ruprecht-Karls-Universitt Heidelberg, Heidelberg; (c)ZITI Institut fr technische Informatik, Ruprecht-Karls-Universitt Heidelberg, Mannheim, Germany 59Faculty of Science, Hiroshima University, Hiroshima, Japan 60Faculty of Applied Information Science, Hiroshima Institute of Technology, Hiroshima, Japan 61Department of Physics, Indiana University, Bloomington IN, United States of America 62Institut fr Astro- und Teilchenphysik, Leopold-Franzens-Universitt, Innsbruck, Austria 63University of Iowa, Iowa City IA, United States of America 114Center for High Energy Physics, University of Oregon, Eugene OR, United States of America 115LAL, Univ. Paris-Sud and CNRS/IN2P3, Orsay, France 116Graduate School of Science, Osaka University, Osaka, Japan 117Department of Physics, University of Oslo, Oslo, Norway 118Department of Physics, Oxford University, Oxford, United Kingdom 119(a)INFN Sezione di Pavia; (b)Dipartimento di Fisica, Universit di Pavia, Pavia, Italy 120Department of Physics, University of Pennsylvania, Philadelphia PA, United States of America 121Petersburg Nuclear Physics Institute, Gatchina, Russia 122(a)INFN Sezione di Pisa; (b)Dipartimento di Fisica E. Fermi, Universit di Pisa, Pisa, Italy 123Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh PA, United States of America 124(a)Laboratorio de Instrumentacao e Fisica Experimental de Particulas - LIP, Lisboa, Portugal; (b)Departamento de Fisica Teorica y del Cosmos and CAFPE, Universidad de Granada, Granada, Spain 125Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic 126Faculty of Mathematics and Physics, Charles University in Prague, Praha, Czech Republic 127Czech Technical University in Prague, Praha, Czech Republic 128State Research Center Institute for High Energy Physics, Protvino, Russia 129Particle Physics Department, Rutherford Appleton Laboratory, Didcot, United Kingdom 130Physics Department, University of Regina, Regina SK, Canada 131Ritsumeikan University, Kusatsu, Shiga, Japan 132(a)INFN Sezione di Roma I; (b)Dipartimento di Fisica, Universit La Sapienza, Roma, Italy 133(a)INFN Sezione di Roma Tor Vergata; (b)Dipartimento di Fisica, Universit di Roma Tor Vergata, Roma, Italy 134(a)INFN Sezione di Roma Tre; (b)Dipartimento di Fisica, Universit Roma Tre, Roma, Italy 135(a)Facult des Sciences Ain Chock, Rseau Universitaire de Physique des Hautes Energies - Universit Hassan II, Casablanca; (b)Centre National de lEnergie des Sciences Techniques Nucleaires, Rabat; (c)Facult des Sciences Semlalia, Universit Cadi Ayyad, LPHEA-Marrakech; (d)Facult des Sciences, Universit Mohamed Premier and LPTPM, Oujda; (e)Facult des Sciences, Universit Mohammed V-Agdal, Rabat, Morocco 136DSM/IRFU (Institut de Recherches sur les Lois Fondamentales de lUnivers), CEA Saclay (Commissariat a lEnergie Atomique), Gif-sur-Yvette, France 137Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz CA, United States of America 138Department of Physics, University of Washington, Seattle WA, United States of America 139Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom 140Department of Physics, Shinshu University, Nagano, Japan 141Fachbereich Physik, Universitt Siegen, Siegen, Germany 142Department of Physics, Simon Fraser University, Burnaby BC, Canada 143SLAC National Accelerator Laboratory, Stanford CA, United States of America 144(a)Faculty of Mathematics, Physics & Informatics, Comenius University, Bratislava; (b)Department of Subnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice, Slovak Republic 145(a)Department of Physics, University of Johannesburg, Johannesburg; (b)School of Physics, University of the Witwatersrand, Johannesburg, South Africa 146(a)Department of Physics, Stockholm University; (b)The Oskar Klein Centre, Stockholm, Sweden 147Physics Department, Royal Institute of Technology, Stockholm, Sweden 148Departments of Physics & Astronomy and Chemistry, Stony Brook University, Stony Brook NY, United States of America 149Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom 150School of Physics, University of Sydney, Sydney, Australia 151Institute of Physics, Academia Sinica, Taipei, Taiwan 152Department of Physics, Technion: Israel Inst. of Technology, Haifa, Israel 153Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel 154Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece 155International Center for Elementary Particle Physics and Department of Physics, The University of Tokyo, Tokyo, Japan 156Graduate School of Science and Technology, Tokyo Metropolitan University, Tokyo, Japan 157Department of Physics, Tokyo Institute of Technology, Tokyo, Japan 158Department of Physics, University of Toronto, Toronto ON, Canada 159(a)TRIUMF, Vancouver BC; (b)Department of Physics and Astronomy, York University, Toronto ON, Canada 160Institute of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan 161Science and Technology Center, Tufts University, Medford MA, United States of America 162Centro de Investigaciones, Universidad Antonio Narino, Bogota, Colombia 163Department of Physics and Astronomy, University of California Irvine, Irvine CA, United States of America 164(a)INFN Gruppo Collegato di Udine, Udine; (b)ICTP, Trieste; (c)Dipartimento di Chimica, Fisica e Ambiente, Universit di Udine, Udine, Italy 165Department of Physics, University of Illinois, Urbana IL, United States of America 166Department of Physics and Astronomy, University of Uppsala, Uppsala, Sweden 167Instituto de Fsica Corpuscular (IFIC) and Departamento de Fsica Atmica, Molecular y Nuclear and Departamento de Ingeniera Electrnica and Instituto de Microelectrnica de Barcelona (IMB-CNM), University of Valencia and CSIC, Valencia, Spain 168Department of Physics, University of British Columbia, Vancouver BC, Canada 169Department of Physics and Astronomy, University of Victoria, Victoria BC, Canada 170Waseda University, Tokyo, Japan 171Department of Particle Physics, The Weizmann Institute of Science, Rehovot, Israel 172Department of Physics, University of Wisconsin, Madison WI, United States of America 173Fakultt fr Physik und Astronomie, Julius-Maximilians-Universitt, Wrzburg, Germany 174Fachbereich C Physik, Bergische Universitt Wuppertal, Wuppertal, Germany 175Department of Physics, Yale University, New Haven CT, United States of America 176Yerevan Physics Institute, Yerevan, Armenia 177Domaine scientifique de la Doua, Centre de Calcul CNRS/IN2P3, Villeurbanne Cedex, France aAlso at Laboratorio de Instrumentacao e Fisica Experimental de Particulas - LIP, Lisboa, Portugal bAlso at Faculdade de Ciencias and CFNUL, Universidade de Lisboa, Lisboa, Portugal cAlso at Particle Physics Department, Rutherford Appleton Laboratory, Didcot, United Kingdom dAlso at TRIUMF, Vancouver BC, Canada eAlso at Department of Physics, California State University, Fresno CA, United States of America fAlso at Novosibirsk State University, Novosibirsk, Russia gAlso at Fermilab, Batavia IL, United States of America hAlso at Department of Physics, University of Coimbra, Coimbra, Portugal iAlso at Universit di Napoli Parthenope, Napoli, Italy jAlso at Institute of Particle Physics (IPP), Canada kAlso at Department of Physics, Middle East Technical University, Ankara, Turkey lAlso at Louisiana Tech University, Ruston LA, United States of America mAlso at Department of Physics and Astronomy, University College London, London, United Kingdom nAlso at Group of Particle Physics, University of Montreal, Montreal QC, Canada oAlso at Department of Physics, University of Cape Town, Cape Town, South Africa pAlso at Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan qAlso at Institut fr Experimentalphysik, Universitt Hamburg, Hamburg, Germany rAlso at Manhattan College, New York NY, United States of America sAlso at School of Physics, Shandong University, Shandong, China tAlso at CPPM, Aix-Marseille Universit and CNRS/IN2P3, Marseille, France uAlso at School of Physics and Engineering, Sun Yat-sen University, Guanzhou, China vAlso at Academia Sinica Grid Computing, Institute of Physics, Academia Sinica, Taipei, Taiwan wAlso at DSM/IRFU (Institut de Recherches sur les Lois Fondamentales de lUnivers), CEA Saclay (Commissariat a lEnergie Atomique), Gif-sur-Yvette, France xAlso at Section de Physique, Universit de Genve, Geneva, Switzerland yAlso at Departamento de Fisica, Universidade de Minho, Braga, Portugal zAlso at Department of Physics and Astronomy, University of South Carolina, Columbia SC, United States of America aaAlso at Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Budapest, Hungary abAlso at California Institute of Technology, Pasadena CA, United States of America acAlso at Institute of Physics, Jagiellonian University, Krakow, Poland adAlso at Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China


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G. Aad, B. Abbott, J. Abdallah, A. A. Abdelalim. Search for anomaly-mediated supersymmetry breaking with the ATLAS detector based on a disappearing-track signature in pp collisions at \(\sqrt{s} = 7~\mathrm{TeV}\), The European Physical Journal C, 2012, 1993, DOI: 10.1140/epjc/s10052-012-1993-2