Measurement of the forward W boson cross-section in pp collisions at √s=7 TeV

JHEP12(2014)079 Published for SISSA by Springer Received:August 20, 2014 Accepted:December 1, 2014 Published:December 10, 2014 Measurement of the forward Wboson cross-section in pp collisions at √s= 7 TeV The LHCb collaboration E-mail: [email protected] Abstract: A measurement of the inclusive W→µν production cross-section using data from pp collisions at a centre-of-mass energy of √s= 7 TeV is presented. The analysis is based on an integrated luminosity of about 1.0 fb−1recorded with the LHCb detector. Results are reported for muons with a transverse momentum greater than 20 GeV/c and pseudorapidity between 2.0 and 4.5. The W+and W−production cross-sections are measured to be σW+→µ+ν= 861.0±2.0±11.2±14.7 pb , σW−→µ−ν= 675.8±1.9±8.8±11.6 pb , where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity determination. Cross-section ratios and differential distributions as functions of the muon pseudorapidity are also presented. The ratio of W+to W−cross-sections in the same fiducial kinematic region is determined to be σW+→µ+ν σW−→µ−ν = 1.274 ±0.005 ±0.009 , where the uncertainties are statistical and systematic, respectively. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Keywords: Hadron-Hadron Scattering, QCD, Forward physics ArXiv ePrint: 1408.4354 Open Access, Copyright CERN, for the benefit of the LHCb Collaboration. Article funded by SCOAP3. doi:10.1007/JHEP12(2014)079 JHEP12(2014)079 Contents 1 Introduction 1 2 Detector and data sets 2 3 Event selection 3 4 Signal yield 4 5 Cross-section measurement 7 5.1 Acceptance 7 5.2 Reconstruction efficiencies 7 5.3 Selection efficiency 8 5.4 Final state radiation 8 5.5 Systematic uncertainties 8 6 Results 10 7 Conclusions 13 A Fit 14 B Tables 15 The LHCb collaboration 20 1 Introduction Measurements of the production cross-section of electroweak bosons constitute an important test of the Standard Model at LHC energies. Theoretical predictions, which are available at next-to-next-to-leading order (NNLO) in perturbative quantum chromodynamics (QCD) [1–5], rely on the parameterisations of the momentum fraction, Bjorken-x, of the partons inside the proton. The uncertainties on the parton density functions (PDFs) of the proton are larger at low Bjorken-xvalues. The forward acceptance of the LHCb experiment, with a pseudorapidity coverage in the range 2 < η < 5, can directly access this region of the phase space to Bjorken-xvalues as low as 10−6and provide constraints on the PDFs that complement those of the ATLAS and CMS experiments [6]. In addition to the determination of the Wboson cross-section, the ratio of W+to W−cross-sections and the Wproduction charge asymmetry allow the Standard Model to be tested with high precision, as experimental and theoretical uncertainties partially cancel. – 1 – JHEP12(2014)079 LHCb has previously reported measurements of inclusive Wand Zboson production in pp collisions at a centre-of-mass energy of √s= 7 TeV to final states containing muons using a data sample corresponding to an integrated luminosity of about 40 pb−1[7]. The impact of the Wresults on the PDF determination was studied and determined to be the largest compared to other LHC Drell-Yan data due to the forward acceptance of the LHCb detector [8,9]. A more precise measurement of the Wproduction can therefore further improve the knowledge of the partonic content of the proton. The analysis presented in this paper is based on a data set collected in 2011, which corresponds to an integrated luminosity of approximately 1.0 fb−1. The contribution of virtual photons to Zboson production is always implied. The inclusive W+and W−cross-sections, σW±→µ±ν, are measured for muons with a transverse momentum, pT, greater than 20 GeV/c and ηbetween 2.0 and 4.5. The differential cross-sections, the W+to W−cross-section ratio, RW, and the muon charge asymmetry, Aµ, are determined in the same fiducial kinematic region in eight bins of muon pseudorapidity. The ATLAS [10] and CMS [11] collaborations already reported measurements of these quantities, although in different kinematic volumes. Measurements are corrected for final state radiation (FSR) of the muon. No corrections are applied for initial state radiation, electroweak effects, and their interplay with QED effects. The paper is organised as follows: section 2describes the LHCb detector as well as the data and the simulation samples used; the selection of the W→µν candidates and the extraction of the signal yield are outlined in sections 3and 4; section 5describes the crosssection measurement and discusses the associated systematic uncertainties; the results are presented in section 6; and section 7concludes the paper. 2 Detector and data sets The LHCb detector [12] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed predominantly for the study of particles containing bor cquarks. The detector includes a high-precision tracking system consisting of a silicon-strip vertex detector surrounding the pp interaction region, a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubes placed downstream of the magnet. The magnet polarity can be reversed, so that left-right detector asymmetry effects can be studied and corrected for in the analyses. The tracking system provides a measurement of momentum, p, with a relative uncertainty that varies from 0.4% at low pvalues to 0.6% at 100 GeV/c. The minimum distance of a track to a primary vertex, the impact parameter (IP), is measured with a resolution of (15 + 29/pT)µm, where the pTis in GeV/c. Different types of charged hadrons are distinguished using information from two ring-imaging Cherenkov detectors. Photon, electron and hadron candidates are identified by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromagnetic and a hadronic calorimeter. Muons are identified by a system composed of alternating layers of iron and multiwire proportional chambers. The trigger consists of a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage, which – 2 – JHEP12(2014)079 applies full event reconstruction. A set of global event cuts that prevents events with high occupancy dominating the processing time of the software trigger is also applied. This measurement is based on data corresponding to an integrated luminosity of 975± 17 pb−1taken in pp collisions at a centre-of-mass energy of 7 TeV. The absolute luminosity scale was measured periodically throughout the data taking period using both Van der Meer scans [13], where the beam profile is determined by moving the beams transversely across each other, and a beam-gas imaging method [14], in which beam-gas interaction vertices near the beam crossing point are reconstructed to determine the beam profile. The two methods give consistent results and the integrated luminosity is determined from their average, with an estimated systematic uncertainty of 1.7% [15]. Simulated data are used to optimise the event selection, estimate the background contamination and check the efficiencies. In the simulation, pp collisions are generated using Pythia [16] with a specific LHCb configuration [17]. Decays of hadronic particles are described by EvtGen [18], in which final state radiation (FSR) is generated using Photos [19]. The interaction of the generated particles with the detector and its response are implemented using the Geant4 toolkit [20,21] as described in ref. [22]. Additional simulated samples of W→µν and Z→µµ events are generated with the program ResBos [23–25] using the CT10 NNLO [26]PDF set. ResBos includes an approximate NNLO O(α2) calculation, plus a next-to-next-to-leading logarithm approximation for the resummation of the soft radiation at low transverse momentum of the vector boson. Results are compared to theoretical predictions calculated with the Fewz [27,28] generator at NNLO for the ABM12 [8], CT10 [26], HERA1.5 [29], JR09 [30], MSTW08 [31] and NNPDF2.3 [9]NNLO PDF sets. The scale uncertainties are estimated by independently varying the renormalisation and factorisation scales by a factor of two around the nominal value, which is set to the boson mass. The total uncertainty for each set corresponds to the PDF (68% CL) and the scale uncertainties added in quadrature. 3 Event selection The signature of a W→µν decay consists of an isolated high transverse momentum muon produced at the pp interaction point. The events must first pass a trigger decision that requires the presence of at least one muon with pT>10 GeV/c. Events are subsequently selected to contain at least one well reconstructed muon with a transverse momentum greater than 20 GeV/c and a pseudorapidity in the range 2.0< η < 4.5. These conditions define the fiducial kinematic region of the measurement. Additional requirements are imposed to discriminate signal candidates from background events. While leptons from electroweak boson decays are expected to be isolated, hadronic QCD processes tend to be associated with jets and produce particles with more activity around them. The muon isolation is described by using the scalar sum of the transverse momentum of all charged particles in the event excluding the candidate, pcone T, in a cone of radius R= 0.5, as well as an analogous variable based on calorimeter information not associated to any track, Econe T. The cone radius is defined as R=p∆η2+ ∆φ2, where ∆η(∆φ) is the difference in pseudorapidity (azimuthal angle) between the muon and the – 3 – JHEP12(2014)079 extra particle. The pcone Tand the Econe Tvariables are required to be smaller than 2 GeV/c and 2 GeV, respectively. Drell-Yan events with two muons within the detector acceptance are removed by vetoing on the presence of a second muon with pT>2 GeV/c. Owing to the long lifetime of the tau lepton, as well as of beauty and charm hadrons, muons produced in Z→ττ,W→τν or semileptonic decays of heavy flavour hadrons mostly originate far from the interaction point where the two protons have collided. Thus selected candidates are required to have an IP <40 µm. Muons typically deposit little energy in the calorimeters in contrast to high-momentum kaons or pions punching through the detector to the muon chambers. Mis-identification due to punchthrough is reduced by requiring Ecalo/pc < 4%, where Ecalo is the sum of the energy deposition in the electromagnetic and hadronic calorimeters associated to the particle. In order to optimise the W→µν selection and evaluate the corresponding efficiency from data, a control sample, pseudo-W, is selected by requiring a pair of well reconstructed tracks identified as muons with an invariant mass, mµµ, within 10 GeV/c2of the nominal Z boson mass. Each of the leptons is alternately masked to mimic the presence of a neutrino and so fake two W→µν decays. A total of 47503 Z→µµ candidates are identified. Given the stringent requirement on the reconstructed dimuon mass, the sample purity is expected to be larger than 99.7%, as observed in ref. [7] within a wider mass window, and so no background subtraction is performed. The pseudo-Wsample is generally in good agreement with W→µν simulation. A small difference is observed in momentumdependent quantities due to a larger average pTin Z→µµ than W→µν decays, which is corrected using simulation. 4 Signal yield A total of 806094 W→µν candidate events fulfil the selection requirements. The signal yield is determined by simultaneously fitting the pTspectra of positively and negatively charged muons in data to the expected shapes for signal and background contributions in eight bins of muon pseudorapidity. A template fit is performed for transverse momenta between 20 and 70 GeV/c using an extended maximum likelihood method based on ref. [32]. The following contributions are considered, where all simulation-based templates are corrected to account for differences in the reconstruction and the selection efficiencies as observed between data and simulation. The W→µν shape, which is defined by the pTof the muon, is modelled using simulation by correcting reconstructed Pythia events with ResBos. The signal normalisation is allowed to vary independently in each bin of muon pseudorapidity and for each charge. The templates of Z→µµ,W→τν and Z→ττ decays with only one muon in the LHCb acceptance are described using simulation. In addition, Z→µµ events are weighted to reproduce the ResBos muon pTdistribution. The normalisation of the electroweak backgrounds is fixed by scaling the number of Zdecays with both muons in the detector acceptance, as reconstructed in the pseudo-Wdata sample, by the probability of having only one muon in LHCb instead of two, as determined from simulation. The number is – 4 – JHEP12(2014)079 IP [mm] 0 0.5 1 1.5 Events per 0.02 mm 10 2 10 3 10 4 10 5 10 6 10 LHCb Data Fit (data)WPseudo- (simulation)ντ →W (simulation)µ X→ c+cbb c / p calo E 0 0.5 1 1.5 Events per 0.02 10 2 10 3 10 4 10 5 10 6 10 LHCb Data Fit (data)WPseudo- Hadrons (data) Figure 1. Fit to (left) the impact parameter distribution and (right) the relative energy deposition in the calorimeters. The data are compared to fitted contributions described in the legends. corrected for differences in reconstructing and selecting Zand Wevents and takes into account acceptance variations between W→τν,Z→ττ and Z→µµ decays. The electroweak backgrounds account for (9.82 ±0.16)% of the total number of candidates, where the uncertainty is statistical and dominated by the size of the pseudo-Wsample. The pTspectrum of semileptonic decays of heavy flavour hadrons is obtained from data by requiring an impact parameter exceeding 100 µm, which selects tracks incompatible with production at a primary vertex. Several IP thresholds are tested with marginal changes to the pTdistribution, as cross-checked on data and simulation. The normalisation is determined via a template fit to the IP distribution in data with three classes of events: muons originating from the pp interaction point, described with pseudo-Wdata, muons coming from W→τν or Z→ττ decays, parameterised with simulation, and muons from heavy flavour hadrons, modelled with a mixture of inclusive bb and cc simulated samples. The result of the fit is shown in figure 1(left) from where the heavy flavour normalisation is determined to be (0.48 ±0.03)%, and constrained in the pTfit. The residual background due to Kand πpunchthrough is determined from data using a template fit. Figure 1(right) shows the fit to the relative energy deposition in the calorimeters, where W→µν candidates are compared to muons and hadrons selected from pseudo-Wand randomly triggered data, respectively. By requiring Ecalo/pc < 4%, kaons or pions punching through the detector to the muon chambers are reduced to a negligible level and therefore not considered when measuring the W→µν yield. Kaons and pions decaying in flight to muons are described using data. Tracks that are not involved in any trigger decision are selected and the corresponding pTis weighted by their probability to decay to muons, as measured on data. The probability is determined as the fraction of reconstructed particles identified as muons, and is found to be consistent with an estimate based on the mean lifetimes and decay distance of simulated Kand πmesons. – 5 – JHEP12(2014)079 ]c [GeV/ T p cEvents per 1 GeV/ 10000 20000 30000 LHCb + µµ < 4.5η2.0 < Data νµ → πK/ Fit Electroweak νµ →W Heavy flavour ]c [GeV/ T p Pull -5 0 5 20 30 40 50 60 7020 30 40 50 60 70 Figure 2. Transverse momentum distribution of the (left panel) positive and (right panel) negative muon candidates in the fiducial pseudorapidity range. The data are compared to fitted contributions described in the legend. The fit residuals normalised to the data uncertainty are shown at the bottom of each distribution. The normalisation of the decay-in-flight background is allowed to vary independently in each ηbin and for each charge. The signal purity, defined as the ratio of signal to candidate event yield, is determined with a fit that relies on the correct description of the pTdistribution in data and thus a good calibration of the momentum scale is needed. The momentum measurement, which is based on the curvature of charged particle trajectories, critically depends on the correct alignment of the LHCb detector and on an accurate knowledge of the magnetic field across the tracking volume. To calibrate the momentum scale for high-pTparticles, di muon pairs are identified with the same criteria used to select the pseudo-Wsample, but with mµµ in the range from 60 to 120 GeV/c2. The calibration is performed in bins of ηand φfor positively and negatively charged muons separately, by exploiting the deviations of the average reconstructed invariant mass from the known Zboson mass. The procedure removes the dependence of mµµ on the direction of flight of the muon, as well as of the pTon the charge of the particle. The result of the fit in the range 2.0< η < 4.5 is presented in figure 2, while figures 8 and 9in appendix Ashow the fit in the eight pseudorapidity bins. The χ2/ndf of the fit is 1.65, with 768 degrees of freedom. The distribution of the normalised fit residuals show an imperfect description of the data by the adopted templates, particularly for negative muons at high pTvalues, however, the effect on the signal yield is small. The W+→µ+ν and W−→µ−νsample purities are determined to be (77.13±0.19)% and (77.39±0.23)%, respectively. – 6 – JHEP12(2014)079 5 Cross-section measurement The inclusive Wboson production cross-section is measured in eight bins of muon ηbetween 2.0 and 4.5, and with the requirement that the muon has a pTabove 20 GeV/c. The crosssection in each pseudorapidity bin is defined as σW±→µ±ν(ηi) = 1 L·NW·ρ±(ηi) A±(ηi)·εrec(ηi)·εsel(ηi)·1 1−f± FSR(ηi), where Lis the integrated luminosity corresponding to the data set used in the analysis and NWis the total number of selected W→µν candidates. The signal purity, ρ±, the acceptance, A±, the reconstruction and the selection efficiencies, εrec and εsel, and the correction for FSR,f± FSR, are determined for each ηbin. The cross-section in the range 2.0< η < 4.5 is obtained by summing over all bins. 5.1 Acceptance The acceptance factor, A±, is used to correct for the reduced pTrange of the fit. The correction is taken from the W→µν ResBos simulation and is defined as the fraction of generated events fulfilling the kinematic requirements of the measurement that have a muon transverse momentum smaller than 70 GeV/c. The average acceptance is 99.3% and 99.1% for W+and W−, respectively. In addition, no significant migration between ηbins is observed and no correction is applied. 5.2 Reconstruction efficiencies The efficiency to reconstruct the muon produced in a W→µν decay, εrec, is determined using data-driven techniques following refs. [7] and [33]. The reconstruction efficiency is factorised as the product of the tracking, the particle identification, the trigger and the global event cut efficiencies. The Z→µµ decay mode provides a highly pure sample of events that is used to determine efficiencies for high-pTmuons via a tag-and-probe method. The tag is a reconstructed track identified as a muon that triggered the event, while a second reconstructible object is used as the probe. The tag and the probe are required to have pTgreater than 20 GeV/c, a pseudorapidity in the range 2.0< η < 4.5, to be associated to the same primary vertex and have a combined invariant mass between 60 and 120 GeV/c2. The efficiency is determined as the fraction of tag-and-probe candidates that fulfil a specific requirement on the probe. The tracking efficiency is determined using a probe track reconstructed by combining hits in the muon stations and the large-area silicon-strip detector, which are not used in the track finding. In order to reduce the background contribution, the accepted mµµ range is restricted to 70 −110 GeV/c2, and the tag and the probe are required to have an azimuthal separation greater than 0.1 rad. The efficiency depends on the probe ηvalue and varies between 87.2% and 97.3%. Simulation is used to correct for possible biases in the method, which range between 0.4% and 2.0%, and the corresponding systematic uncertainty is combined in quadrature with the statistical precision of the determination. The total uncertainty on the tracking efficiency varies between 0.4% and 1.0%. – 7 – JHEP12(2014)079 The efficiency for identifying a muon is measured using a reconstructed track as the probe lepton. The tag and the probe are required to be isolated (pcone T<2 GeV/c) and to have an azimuthal separation greater than 2.7 rad to ensure a sample of very high purity. The use of the isolation requirement is investigated in simulation and proved not to bias the efficiency determination. The muon identification efficiency is found to vary between 95.6% and 98.8% as a function of the probe pseudorapidity. The corresponding uncertainty is about 0.2% and accounts for the small amount of residual background. The trigger efficiency is evaluated by using an identified muon as the probe object. To reduce the background to a negligible level, an isolation requirement (pcone T<2 GeV/c) is applied to the tag and the probe. The measurement is not biased by the requirement on the pcone T, as verified using simulation. The efficiency depends on the ηvalue of the probe and ranges between 77.6% and 81.5%. The trigger efficiency uncertainty corresponds to the statistical uncertainty only and varies between 0.4% and 0.6%. To account for losses due to a high event occupancy in the hardware trigger, the global event cut efficiency is determined from data using a dimuon trigger with a relaxed threshold. The efficiency depends on the event multiplicity. After correcting for occupancy differences between Z and Wevents, this is determined to be (95.9±1.1)%. The reconstruction efficiencies are checked against simulation, for dependences on the muon charge as well as other quantities. No biases are observed. 5.3 Selection efficiency The efficiency to select W→µν events, εsel, defined as the fraction of events that fulfil the requirements used to identify the candidates, is measured using the pseudo-Wsample. Good agreement is observed between pseudo-Wdata and W→µν simulation; however, the larger average pTof pseudo-Wevents must be accounted for. Simulation is used to asses the difference due to measuring the selection efficiency with muons produced in Zinstead of Wboson decays, which on average amounts to about 2%. The statistical uncertainty of the data-driven determination and of the simulation-based correction are summed in quadrature. The efficiency is found to vary as a function of the muon pseudorapidity. No dependence on the lepton charge is observed except for the most forward ηbin. The measured εsel ranges between 61.9% and 70.0% in the central bins with an uncertainty of about 0.5%, but decreases to 49.0% in the first pseudorapidity bin. The efficiency to select W+and W−in the range 4.0< η < 4.5 is (34.1±0.8)% and (29.3±0.7)%, respectively. 5.4 Final state radiation The FSR correction, f± FSR, is evaluated using Photos interfaced to Pythia as the ratio of the number of generated events that after photon radiation fail the kinematic requirements to the number of generated decays that before FSR satisfy the same criteria. The correction in bins of muon pseudorapidity is reported in appendix B(table 2). 5.5 Systematic uncertainties The contributions to the systematic uncertainty considered in the analysis are the shape and the normalisation of the templates used in the fit, the reconstruction and the selection – 8 – JHEP12(2014)079 ]c [GeV/ T p cEvents per 1 GeV/ 1000 2000 3000 4000 LHCb + µµ < 3.25η3.00 < Data νµ → πK/ Fit Electroweak νµ →W Heavy flavour ]c [GeV/ T p Pull -5 0 5 20 30 40 50 60 7020 30 40 50 60 70 ]c [GeV/ T p cEvents per 1 GeV/ 1000 2000 3000 4000 LHCb + µµ < 3.50η3.25 < ]c [GeV/ T p Pull -5 0 5 20 30 40 50 60 7020 30 40 50 60 70 ]c [GeV/ T p cEvents per 1 GeV/ 1000 2000 3000 4000 LHCb + µµ < 4.00η3.50 < ]c [GeV/ T p Pull -5 0 5 20 30 40 50 60 7020 30 40 50 60 70 ]c [GeV/ T p cEvents per 1 GeV/ 200 400 600 800 1000 LHCb + µµ < 4.50η4.00 < ]c [GeV/ T p Pull -5 0 5 20 30 40 50 60 7020 30 40 50 60 70 Figure 9. Transverse momentum distribution of the (left panel) positive and (right panel) negative muon candidates in eight bins of pseudorapidity. The data are compared to fitted contributions described in the legend. The fit residuals normalised to the data uncertainty are shown at the bottom of each distribution. B Tables η f+ FSR [%] f− FSR [%] (2.00,2.25) 1.62 ±0.39 1.84 ±0.30 (2.25,2.50) 1.75 ±0.41 1.46 ±0.28 (2.50,2.75) 2.41 ±0.50 1.03 ±0.25 (2.75,3.00) 1.43 ±0.40 0.72 ±0.23 (3.00,3.25) 2.01 ±0.50 0.93 ±0.31 (3.25,3.50) 1.51 ±0.48 1.71 ±0.51 (3.50,4.00) 2.32 ±0.50 1.22 ±0.45 (4.00,4.50) 2.05 ±0.47 0 Table 2. Correction for final state radiation for W+→µ+νand W−→µ−νin bins of muon pseudorapidity. No loss due FSR is observed for W−in the last pseudorapidity bin because of lack of statistics. – 15 – JHEP12(2014)079 η σW+→µ+ν[ pb ] σW−→µ−ν[ pb ] (2.00,2.25) 188.4±1.2±4.0±3.2 108.9±0.9±2.4±1.9 (2.25,2.50) 175.3±0.9±3.6±3.0 102.8±0.7±2.2±1.8 (2.50,2.75) 151.3±0.8±2.6±2.6 94.2±0.7±1.6±1.6 (2.75,3.00) 120.3±0.7±2.0±2.1 86.7±0.6±1.8±1.5 (3.00,3.25) 92.4±0.6±1.6±1.6 79.0±0.6±1.6±1.4 (3.25,3.50) 60.4±0.5±1.1±1.0 67.2±0.5±1.6±1.1 (3.50,4.00) 58.8±0.5±1.0±1.0 94.0±0.7±1.6±1.6 (4.00,4.50) 14.1±0.4±0.4±0.2 42.9±0.7±1.3±0.7 Table 3. Inclusive cross-section for W+and W−boson production in bins of muon pseudorapidity. The uncertainties are statistical, systematic and luminosity. η RW (2.00,2.25) 1.730 ±0.018 ±0.030 (2.25,2.50) 1.706 ±0.015 ±0.040 (2.50,2.75) 1.606 ±0.014 ±0.021 (2.75,3.00) 1.388 ±0.013 ±0.024 (3.00,3.25) 1.169 ±0.012 ±0.021 (3.25,3.50) 0.898 ±0.010 ±0.025 (3.50,4.00) 0.626 ±0.007 ±0.006 (4.00,4.50) 0.328 ±0.011 ±0.011 Table 4. Ratio of W+to W−cross-section in bins of muon pseudorapidity. The uncertainties are statistical and systematic. η Aµ[%] (2.00,2.25) 26.74 ±0.48 ±0.82 (2.25,2.50) 26.08 ±0.41 ±1.09 (2.50,2.75) 23.25 ±0.42 ±0.60 (2.75,3.00) 16.26 ±0.46 ±0.84 (3.00,3.25) 7.81 ±0.50 ±0.90 (3.25,3.50) −5.37 ±0.57 ±1.35 (3.50,4.00) −23.04 ±0.52 ±0.49 (4.00,4.50) −50.65 ±1.22 ±1.30 Table 5. Lepton charge asymmetry in bins of muon pseudorapidity. The uncertainties are statistical and systematic. – 16 – JHEP12(2014)079 (2.00,2.25) (2.25,2.50) (2.50,2.75) (2.75,3.00) (3.00,3.25) (3.25,3.50) (3.50,4.00) (4.00,4.50) + 1 (2.00,2.25) −0.60 1 + 0.13 0.48 1 (2.25,2.50) −0.45 0.03 0.34 1 + 0.26 0.42 0.48 0.20 1 (2.50,2.75) −0.44 0.15 0.16 0.52 0.64 1 + 0.42 0.22 0.24 0.46 0.36 0.49 1 (2.75,3.00) −0.10 0.50 0.59 −0.04 0.48 0.12 0.51 1 + 0.23 0.41 0.47 0.17 0.46 0.28 0.33 0.49 1 (3.00,3.25) −0.45 0.03 0.02 0.58 0.21 0.53 0.47 −0.03 0.49 1 + 0.17 0.45 0.53 0.06 0.46 0.20 0.28 0.56 0.46 0.07 1 (3.25,3.50) −0.46 −0.06 −0.09 0.61 0.12 0.53 0.46 −0.15 0.09 0.62 0.19 1 + 0.29 0.37 0.42 0.25 0.45 0.34 0.38 0.41 0.42 0.26 0.41 0.19 1 (3.50,4.00) −0.43 0.20 0.21 0.49 0.35 0.50 0.48 0.18 0.31 0.50 0.24 0.49 0.66 1 + 0.11 0.22 0.27 0.06 0.26 0.11 0.15 0.26 0.23 0.07 0.23 0.01 0.22 0.17 1 (4.00,4.50) −0.20 0.14 0.15 0.22 0.21 0.24 0.24 0.13 0.19 0.23 0.15 0.21 0.21 0.25 0.21 1 +−+−+−+−+−+−+−+− Table 6. 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Zvyagin38. 1Centro Brasileiro de Pesquisas F´ısicas (CBPF), Rio de Janeiro, Brazil 2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil 3Center for High Energy Physics, Tsinghua University, Beijing, China 4LAPP, Universit´e de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France 5Clermont Universit´e, Universit´e Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France 6CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France 7LAL, Universit´e Paris-Sud, CNRS/IN2P3, Orsay, France 8LPNHE, Universit´e Pierre et Marie Curie, Universit´e Paris Diderot, CNRS/IN2P3, Paris, France 9Fakult¨at Physik, Technische Universit¨at Dortmund, Dortmund, Germany 10 Max-Planck-Institut f¨ur Kernphysik (MPIK), Heidelberg, Germany 11 Physikalisches Institut, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg, Germany 12 School of Physics, University College Dublin, Dublin, Ireland 13 Sezione INFN di Bari, Bari, Italy 14 Sezione INFN di Bologna, Bologna, Italy 15 Sezione INFN di Cagliari, Cagliari, Italy 16 Sezione INFN di Ferrara, Ferrara, Italy 17 Sezione INFN di Firenze, Firenze, Italy 18 Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy 19 Sezione INFN di Genova, Genova, Italy 20 Sezione INFN di Milano Bicocca, Milano, Italy 21 Sezione INFN di Milano, Milano, Italy 22 Sezione INFN di Padova, Padova, Italy 23 Sezione INFN di Pisa, Pisa, Italy 24 Sezione INFN di Roma Tor Vergata, Roma, Italy 25 Sezione INFN di Roma La Sapienza, Roma, Italy 26 Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Krak´ow, Poland 27 AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science, Krak´ow, Poland 28 National Center for Nuclear Research (NCBJ), Warsaw, Poland – 22 – JHEP12(2014)079 29 Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania 30 Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia 31 Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia 32 Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia 33 Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia 34 Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia 35 Institute for High Energy Physics (IHEP), Protvino, Russia 36 Universitat de Barcelona, Barcelona, Spain 37 Universidad de Santiago de Compostela, Santiago de Compostela, Spain 38 European Organization for Nuclear Research (CERN), Geneva, Switzerland 39 Ecole Polytechnique F´ed´erale de Lausanne (EPFL), Lausanne, Switzerland 40 Physik-Institut, Universit¨at Z¨urich, Z¨urich, Switzerland 41 Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands 42 Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands 43 NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine 44 Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine 45 University of Birmingham, Birmingham, United Kingdom 46 H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom 47 Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 48 Department of Physics, University of Warwick, Coventry, United Kingdom 49 STFC Rutherford Appleton Laboratory, Didcot, United Kingdom 50 School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 51 School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 52 Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 53 Imperial College London, London, United Kingdom 54 School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 55 Department of Physics, University of Oxford, Oxford, United Kingdom 56 Massachusetts Institute of Technology, Cambridge, MA, United States 57 University of Cincinnati, Cincinnati, OH, United States 58 University of Maryland, College Park, MD, United States 59 Syracuse University, Syracuse, NY, United States 60 Pontif´ıcia Universidade Cat´olica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated to 2 61 Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China, associated to 3 62 Institut f¨ur Physik, Universit¨at Rostock, Rostock, Germany, associated to 11 63 National Research Centre Kurchatov Institute, Moscow, Russia, associated to 31 64 Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain, associated to 36 65 KVI - University of Groningen, Groningen, The Netherlands, associated to 41 66 Celal Bayar University, Manisa, Turkey, associated to 38 aUniversidade Federal do Triˆangulo Mineiro (UFTM), Uberaba-MG, Brazil bP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia cUniversit`a di Bari, Bari, Italy dUniversit`a di Bologna, Bologna, Italy eUniversit`a di Cagliari, Cagliari, Italy fUniversit`a di Ferrara, Ferrara, Italy gUniversit`a di Firenze, Firenze, Italy – 23 – JHEP12(2014)079 hUniversit`a di Urbino, Urbino, Italy iUniversit`a di Modena e Reggio Emilia, Modena, Italy jUniversit`a di Genova, Genova, Italy kUniversit`a di Milano Bicocca, Milano, Italy lUniversit`a di Roma Tor Vergata, Roma, Italy mUniversit`a di Roma La Sapienza, Roma, Italy nUniversit`a della Basilicata, Potenza, Italy oAGH - University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications, Krak´ow, Poland pLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain qHanoi University of Science, Hanoi, Viet Nam rUniversit`a di Padova, Padova, Italy sUniversit`a di Pisa, Pisa, Italy tScuola Normale Superiore, Pisa, Italy uUniversit`a degli Studi di Milano, Milano, Italy – 24 –