Measurement of differential cross sections in the kinematic angular variable ϕ* for inclusive Z boson production in pp collisions at $$ \sqrt{s}=8 $$ TeV

Journal of High Energy Physics, Mar 2018

Abstract Measurements of differential cross sections dσ/dϕ* and double-differential cross sections d2σ/dϕ*d|y| for inclusive Z boson production are presented using the dielectron and dimuon final states. The kinematic observable ϕ* correlates with the dilepton transverse momentum but has better resolution, and y is the dilepton rapidity. The analysis is based on data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb−1. The normalised cross section (1/σ) dσ/dϕ*, within the fiducial kinematic region, is measured with a precision of better than 0.5% for ϕ* < 1. The measurements are compared to theoretical predictions and they agree, typically, within few percent. Open image in new window

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Measurement of differential cross sections in the kinematic angular variable ϕ* for inclusive Z boson production in pp collisions at $$ \sqrt{s}=8 $$ TeV

HJE Measurement of di erential cross sections in the Measurements of di erential cross sections d =d sections d2 =d djyj for inclusive Z boson production are presented using the dielectron and dimuon nal states. The kinematic observable momentum but has better resolution, and y is the dilepton rapidity. The analysis is based on data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb 1 . The normalised cross section (1= ) d =d , within the ducial kinematic region, is measured with a precision of better than 0.5% Hadron-Hadron scattering (experiments); Particle correlations and uctua- - boson 8 TeV p The CMS collaboration for < 1. The measurements are compared to theoretical predictions and they agree, typically, within few percent. 1 Introduction 2 3 4 5 6 7 8 9 The CMS detector Event reconstruction and selection Monte Carlo simulation Analysis method Background estimation Unfolding Systematic uncertainties Theoretical predictions 10 Results 11 Summary The CMS collaboration 1 Introduction The neutral current Drell-Yan (DY) process, qq ! Z= ! `+` , where ` is either an electron or a muon, is one of the best studied physics processes at the CERN LHC. The total and di erential cross sections have been calculated theoretically at next-to-next-toleading order (NNLO) accuracy in the strong coupling S [1{4]. The di erential cross section as a function of dilepton invariant mass d =dm`` has been measured by the LHC experiments at di erent centre-of-mass energies [5{8]. Theoretical calculations reproduce the measurements over nine orders of magnitude at the level of a few percent. The large production cross section and the experimentally clean nal state of the DY process allow for detailed studies of kinematic distributions that serve as stringent tests of the perturbative calculations. One of the most interesting observables is the transverse momentum qT of the Z boson, which is related to its production mechanism. The lower range of qT values are caused by multiple soft-gluon emissions, whereas high qT values result from the emission of one or more hard partons in association with the Z boson. Another interesting observable is the rapidity y of the Z boson which depends on the di erence in { 1 { p momentum between the parent partons in the colliding protons; therefore, the cross section as a function of y depends on the parton distribution functions (PDF). The qT spectrum of the Z boson has been measured by the ATLAS, CMS and LHCb Collaborations at s = 7 TeV [9{11]. Recently, both the CMS and ATLAS Collaborations have extended the study at 8 TeV by performing double-di erential measurements as functions of qT and y [12, 13]. Calculations based on xed-order perturbative quantum chromodynamics (QCD) [14] describe these measurements fairly well. A thorough understanding of the qT spectra of the electroweak vector bosons is essential for high-precision measurements at the LHC, in particular that of the mass of the W boson. Furthermore, the theoretical calculation of the transverse momentum distriform factors [15], which are closely related to those appearing in the calculations for qT. Thus precise measurements of vector boson production are important for validating the theoretical calculations of Higgs boson production at the LHC. An important issue in the accurate measurement of the di erential cross section d =dqT is the experimental resolution of qT, which is dominated by the uncertainties in the magnitude of the transverse momenta of the leptons from the decay of the Z boson. The angles subtended by the leptons, however, are measured more precisely due to the excellent spatial resolution of the CMS tracking system. A kinematic quantity [16{18], derived from these angles, is de ned by the expression = tan 2 sin( ): (1.1) section d 2 =d integrated luminosity of L = 19:7 djyj in CMS at p 0:5 fb 1 . The variable is the opening angle between the leptons in the plane transverse to the beam axis. The variable indicates the scattering angle of the dileptons with respect to the beam in the boosted frame where the leptons are aligned. It is related to the pseudorapidities of the oppositely charged leptons by the relation cos( ) = tanh[ =2], where is the di erence in pseudorapidity between the two leptons. By construction, is greater than zero. Since depends on angular variables, the resolution of is signi cantly better than that of qT, especially at low qT values. Since qT=m``, the range 1 corresponds to qT up to about 100 GeV for a dilepton mass close to the nominal Z boson mass. The cross sections for the DY process as a function of the D0 Collaboration at the Tevatron for pp collisions at p have been measured by s = 1:96 TeV [19] and at the LHC by the ATLAS Collaboration for pp collisions at 7 and 8 TeV [13, 20]. In this paper, the measurements of the di erential cross section d =d and the double-di erential cross s = 8 TeV are pr (...truncated)


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The CMS collaboration, A. M. Sirunyan, A. Tumasyan, W. Adam, F. Ambrogi, E. Asilar, T. Bergauer, J. Brandstetter, E. Brondolin, M. Dragicevic, J. Erö, M. Flechl, M. Friedl, R. Frühwirth, V. M. Ghete, J. Grossmann, J. Hrubec, M. Jeitler, A. König, N. Krammer, I. Krätschmer, D. Liko, T. Madlener, I. Mikulec, E. Pree, N. Rad, H. Rohringer, J. Schieck, R. Schöfbeck, M. Spanring, D. Spitzbart, W. Waltenberger, J. Wittmann, C.-E. Wulz, M. Zarucki, V. Chekhovsky, V. Mossolov, J. Suarez Gonzalez, E. A. De Wolf, D. Di Croce, X. Janssen, J. Lauwers, M. Van De Klundert, H. Van Haevermaet, P. Van Mechelen, N. Van Remortel, S. Abu Zeid, F. Blekman, J. D’Hondt, I. De Bruyn, J. De Clercq, K. Deroover, G. Flouris, D. Lontkovskyi, S. Lowette, S. Moortgat, L. Moreels, Q. Python, K. Skovpen, S. Tavernier, W. Van Doninck, P. Van Mulders, I. Van Parijs, D. Beghin, H. Brun, B. Clerbaux, G. De Lentdecker, H. Delannoy, B. Dorney, G. Fasanella, L. Favart, R. Goldouzian, A. Grebenyuk, G. Karapostoli, T. 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Radziej, H. Reithler. Measurement of differential cross sections in the kinematic angular variable ϕ* for inclusive Z boson production in pp collisions at $$ \sqrt{s}=8 $$ TeV, Journal of High Energy Physics, 2018, pp. 172, Volume 2018, Issue 3, DOI: 10.1007/JHEP03(2018)172