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Physics
Letters
B
www.elsevier.com/locate/physletb
Measurement
of
W
±
and
Z -boson
production
cross
sections
in
pp
collisions
at
√
s
=
13 TeV with
the
ATLAS
detector
.TheATLASCollaboration
a r t i c l e i n f o a b s t ra c t
Article history: Received31March2016
Receivedinrevisedform6June2016 Accepted10June2016
Availableonline15June2016 Editor:W.-D.Schlatter
Measurements of the W±→ ±ν and Z→ +− productioncross sections (where ±=e±,μ±) in proton–proton collisions at√s=13 TeV arepresented usingdata recorded bythe ATLASexperiment at the Large Hadron Collider, corresponding to a total integrated luminosity of 81 pb−1. The total inclusiveW±-bosonproductioncrosssectionstimesthesingle-lepton-flavourbranchingratiosareσtot
W+=
11.83±0.02 (stat)±0.32 (sys)±0.25 (lumi) nb andσtot
W−=8.79±0.02 (stat)±0.24 (sys)±0.18 (lumi) nb
for W+ and W−, respectively. The total inclusive Z -boson production cross section times leptonic branchingratio,withintheinvariantmasswindow66<m<116 GeV,isσZtot=1.981±0.007 (stat)±
0.038 (sys)±0.042 (lumi) nb.TheW+,W−,and Z -bosonproductioncrosssectionsand cross-section ratioswithinafiducialregiondefinedbythedetectoracceptancearealsomeasured. Thecross-section ratios benefit from significant cancellation of experimental uncertainties, resulting in σfid
W+/σ
fid
W−=
1.295±0.003 (stat)±0.010 (sys) andσfid
W±/σZfid=10.31±0.04 (stat)±0.20 (sys).Theoreticalpredictions,
based oncalculations accurateto next-to-next-to-leading orderfor quantum chromodynamics and to next-to-leadingorderforelectroweakprocessesandwhichemploydifferentpartondistributionfunction sets,arecomparedtothesemeasurements.
©2016TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.
1. Introduction
Measurementsofelectroweakvector–bosonproductionat had-ron colliders provide a benchmark for the understanding of quantumchromodynamic(QCD) andelectroweak(EW)processes. Predictions are available up to next-to-next-to-leading-order (NNLO) accuracy in QCD and includeEW correctionsat next-to-leading-order (NLO) accuracy [1]. The cross-section predictions depend onthe parton distribution functions(PDFs)and are thus sensitive to the underlying dynamics of strongly interacting par-ticles.Therefore,measurements of W± and Z -boson1 production
offera unique opportunity to test models ofparton dynamicsat the LargeHadron Collider’s (LHC) [2] newhigher centre-of-mass energyof√s=13 TeV.
Thispaperdescribesmeasurementsoftheinclusiveproduction crosssectionstimesleptonicbranchingratiosforthe W±→e±ν,
W±→μ±ν, Z →e+e−, and Z →μ+μ− processes. Measure-mentsofthecross-sectionratiosofW+ toW−productionandof
W±toZ productionarealsopresented.Allmeasurementsare
per-formedwithproton–proton(pp)collisiondatacorrespondingtoan
E-mail address:[email protected].
1 Throughoutthispaper, Z/γ∗-bosonproductionisdenotedsimplybyZ -boson production.
integrated luminosity of 81 pb−1, collected at√s=13 TeV with the ATLAS detector [3]. The data were collected during the pe-riodofJune13toJuly16,2015,atwhichpointtheLHCcirculated 6.5 TeV beamswith50 nsbunch spacing. Thepeak delivered in-stantaneousluminositywasL=1.7×1033cm−1s−1andthemean numberofpp interactionsperbunchcrossing(hardscatteringand pile-upevents)wasμ=19.
2. Methodologyofcross-sectionmeasurementandpredictions ThetotalproductioncrosssectionfortheW± bosontimesthe branchingratiofordecaysintoasingle-leptonflavour±=e±, μ± (σtot
W±, σ tot W+,and σ
tot
W−)canbeexpressedasaratioofthenumbers ofbackground-subtracteddataevents N totheproductofthe in-tegratedluminosity of thedata L, an acceptancefactor A,anda correctionfactorC :
σtot=L N
·A·C. (1)
The cross sections are defined similarly for the Z boson in the dileptoninvariant massrange66<m<116 GeV (σZtot).The ac-ceptancefactor A isexpressedasthefractionofdecayssatisfying thefiducialacceptance(geometricandkinematicrequirements)at the Monte Carlo generator level. The correction factor C is the ratio of the total number of generated events which pass the
http://dx.doi.org/10.1016/j.physletb.2016.06.023
0370-2693/©2016TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3.
final selectionrequirementsafterreconstruction tothetotal num-ber of generated events within the fiducial acceptance. This fac-tor,defined beforethe decayleptons emit photonsvia final-state radiation (Born-level FSR), includes the efficiencies for triggering on, reconstructing, and identifying the W± and Z -boson decay products within the acceptance, andalso accounts forthe slight difference between the fiducial and reconstructed phase spaces. Theproductioncrosssectionsdefinedwithouttheacceptance fac-tors (σtot·A) arereferred to asthefiducial crosssections(σfid
W±, σfid W+, σ fid W−,and σ fid
Z ).Forthe W±-bosonmeasurement,the fidu-cial phase space is defined by the lepton transverse momentum
p
T>25 GeV, the lepton pseudorapidity
2 |η
|<2.5, the neutrino
transversemomentumpνT>25 GeV,andtheW±-bosontransverse mass3m
T>50 GeV.Similarly, Z -bosonproductionismeasuredin the fiducialphase spacedefined by pT>25 GeV, |η|<2.5, and
66<m<116 GeV.
Theoretical predictions of the fiducialand total cross sections are computed using DYNNLO 1.5 [4,5] for the central value and Fewz3.1[1,6–8]forallvariations reflectingsystematic uncertain-ties, thereby providing full NNLO QCD calculations. The NLO EW corrections are calculated with Fewz 3.1 for Z bosons and with theMonte Carloprogram Sanc[9,10] for W± bosons.The calcu-lationisdone in the Gμ EWscheme[11].The crosssectionsare calculated for vector–boson decays into leptons at Born level, to matchthedefinitionoftheC factor usedinEq.(1)forthe deter-mination of the measured cross sectionsin the data. Thus, from complete NLO EW corrections the following components are in-cluded: virtual QED and weak corrections, initial-state radiation (ISR)andinterferencebetweenISRandFSR[12].Forthe Z -boson
production, all the predictions include the 66<m<116 GeV
requirement. The NNLO PDFs CT14nnlo [13], NNPDF3.0 [14], MMHT14nnlo68CL [15], ABM12 [16], HERAPDF2.0nnlo [17], and ATLAS-epWZ12nnlo[18] areused inthe comparisonstodata, al-though CT14nnloisusedasthebaselineforthepredictions.
The systematicuncertainties inthe predictions are dominated bytheimperfectknowledgeoftheprotonpartondistribution func-tions.Theseuncertaintiesareobtainedfromthesuminquadrature ofthedifferencesbetweenthe centralPDF valuesandthe eigen-vectorsoftherespectivePDFsets.Whereappropriate,asymmetric uncertaintiesaredetermined usingseparate sumsofnegative and positivevariations.The CT14nnlouncertainties(rescaledfrom90% to 68% confidence level (CL)) are used in the comparisonto the measured cross sections in Table 3 of Section 7. The QCD scale uncertainties are defined by the symmetrised envelope of vari-ations in which the renormalisation (μR) and factorisation (μF) scalesarechangedbyfactorsoftwowithanadditionalconstraint of 0.5≤μR/μF≤2. The dynamic scale m andfixed scale mW are used as the central values for the Z boson and W± boson predictions, respectively. A significant component of these scale uncertainties originates fromthe statisticalprecision ofthe inte-gration method used to evaluate the variations. The other sys-tematic uncertainties under consideration (labelled as “other” in Table 3) are asfollows.The uncertainties dueto the strong cou-plingconstantareestimatedfollowingtheprescriptiongivenwith the CT14nnloPDF, varying αSby±0.001 tocorrespondto68% CL. The beamenergyisassumedto be knownto 1% (fromRef. [19],
2 ATLASusesaright-handedcoordinatesystemwithitsoriginatthenominal in-teractionpoint(IP)inthecentreofthedetectorandthe z-axis alongthebeampipe. The x-axis pointsfromtheIPtothecentreoftheLHCring,andthe y-axis points upward.Cylindricalcoordinates(r,φ)areusedinthetransverseplane,φbeingthe azimuthalanglearoundthebeampipe.Thepseudorapidityisdefinedintermsof thepolarangleθasη= −ln tan(θ/2).
3 mT=2p
TpνT[1−cos(φ− φν)] withazimuthalangleofthechargedlepton
φandazimuthalangleoftheneutrinoφν.
with an additional uncertainty to take into account the extrapo-lationofthisuncertaintyto13 TeV).The limitationsofthe NNLO calculationsareestimatedbycomparingthepredictionscalculated with DYNNLO 1.5 and with Fewz 3.1. For the total cross-section predictions, thesedifferencesarefound to be <0.2% per process andhencearenegligible.Forthefiducialcross-sectionpredictions, these differences are larger due to a feature of the calculations involving leptons with symmetric pT requirements, resulting in consistentlylargervaluesfrom Fewz.Thedifferencesarecalculated usingthe CT14nnloPDFasacentralvalueinbothcases,andareup to1.3%fortheW±-bosoncrosssectionsand0.6%forthe Z -boson
cross section. These differences are however not included in the predictionuncertaintiesgivenin Table 3ofSection7.
Predictions forthefiducial cross-section ratios σfid W+/σ fid W− and σfid W±/σ fid
Z arealsocalculated,withtheircorrespondingPDF uncer-tainties consideredasfullycorrelated,eigenvectorby eigenvector, inthe ratios.TheQCD scalevariations are notconsidered forthe ratiossincethehigher-ordercorrectionsareexpectedtoaffectboth
the W± and Z bosons in a similar mannerbut the exact
corre-lation is difficult to evaluate. The differences between Fewz and DYNNLOfor W+/W−and W±/Z are0.4% and0.6%,respectively, andarenotincludedinthepredictionuncertaintiesof Table 3.The remaining theoretical uncertainties evaluatedinthe fiducialcross sectionsmentioned abovelargely cancelintheratioandare also neglected.
The acceptancefactors A arealsocalculatedwith DYNNLO 1.5 for the central value and Fewz 3.1 for variations accounting for systematic uncertainties.Their uncertainties are derived from the envelope of the PDF variations of CT14nnlo, NNPDF3.0, MMHT14nnlo68CL,and ABM12.Calculationsoftheacceptance fac-tors obtainedfromeitherthesignal MonteCarlosimulationused in this analysis (Powheg + Pythia 8 [20–23], fullydescribed in Section 3) or from Fewz fall within this envelope. In addition, uncertainties due to parton showers and the hadronisation de-scriptionaretakenfromapreviouspublication[24],afterchecking theirvalidityforthe13 TeVresult,andwerederivedasthe differ-enceintheacceptancescalculatedwith Powheg-Box v1butusing differentmodelsforpartonshowerandhadronisationdescriptions, namelythe Herwig[25]or Pythia[26]programs.
3. Simulationsamples
MonteCarlosimulationsareusedtoevaluatetheselection effi-ciencyforsignaleventsandthecontributionofseveralbackground processestotheanalyseddataset.Allofthesamplesareprocessed withthe Geant4-basedsimulation[27]oftheATLASdetector[28]. Nearlyall oftheprocessesofinterest, specificallyevents
contain-ing W±or Z bosons[29],aregeneratedwiththe Powheg-Box v2
MonteCarloprograminterfacedtothe Pythia 8.186partonshower model.The CT10PDF set[30] isused inthematrix elementand the AZNLO [31] setof generator-parameter values(tune)is used, withPDFsetCTEQ6L1[32],forthemodellingofnon-perturbative effects. The EvtGen v.1.2.0 program [33] is used for properties of the bottom and charm hadron decays, and Photos++ version 3.52[34,35] isused forQEDemissionsfromelectroweakvertices and charged leptons. Samples of top-quark pair (tt) and single-top-quarkproductionaregeneratedwiththe Powheg-Boxv2 gen-erator, which uses the four-flavour scheme for the NLO matrix element calculationstogether withthe fixedfour-flavour PDF set CT10f4. For all top-quark processes, top-quark spin correlations are preserved. The partonshower, fragmentation, andunderlying event are simulated using Pythia 6.428 with the CTEQ6L1 PDF sets andthe corresponding Perugia 2012 tune (P2012) [36]. The top-quark mass is set to 172.5 GeV. The EvtGen v1.2.0 program is used for properties of the bottom and charm hadron decays.
Diboson processesare simulatedusing the Sherpa v2.1.1 genera-tor[37].Multipleoverlaid pp collisionsaresimulatedwiththesoft QCD processes of Pythia v.8.186using the A2tune [38] andthe MSTW2008LO PDF[39].TheMonteCarloeventsarereweightedso thattheμdistributionmatchestheobservedpile-updistribution inthe data. For the comparisonto data in the distributions, the single-bosonMonteCarlosimulationsarenormalised tothecross sectionsmeasuredbythisanalysis.Intheevaluationofthe single-bosonEW backgroundsforthe cross-sectioncalculations, simula-tions are instead normalised to the results of higher-order QCD calculations, withuncertainties of5%. The remaining simulations are also normalised to the predictions of higher-order QCD cal-culations,withuncertaintiesof 6%forthe dibosonandtop-quark processes.
4. Eventselection
Electronandmuoncandidateeventsareselectedusingtriggers whichrequireatleastone electronormuonwithtransverse mo-mentumthresholds of pT=24 GeV or 20 GeV,respectively, with looseisolation requirements. Torecover possibleefficiency losses athighmomenta,additionalelectronandmuontriggerswhichdo notmakeanyisolationrequirementsareincludedwiththresholds ofpT=60 GeV and50 GeV,respectively.
Electroncandidates are required to have pT>25 GeV and to pass the “medium” likelihood-based identification requirements [40,41] optimised for the 2015 operating conditions, within the fiducialregionof|η|<2.47,excludingcandidatesinthetransition region betweenthe barreland endcapelectromagnetic calorime-ters,1.37<|η|<1.52.Muonsarereconstructedfor|η|<2.4 with
pT>25 GeV andmust passthe “medium”identification require-ments [42] also optimised for the 2015 operating conditions. At leastoneoftheleptoncandidatesisrequiredtomatchthelepton thattriggeredtheevent.Theelectronsandmuonsmustalsosatisfy
pT-dependentcone-basedisolationrequirements,usingboth track-ing detector andcalorimeter information (described in Refs. [43, 44],respectively).Theisolationrequirementsaretunedsothatthe leptonisolation efficiencyis atleast90% forall pT>25 GeV, in-creasingto99%at60 GeV.
Jetsarereconstructed fromenergydepositsinthe calorimeter using the anti-kt algorithm [45] with radius parameter R=0.4. Alljets[46],withenergiescalibratedattheelectromagneticscale, musthavepT>20 GeV and|η|<4.5.Themissingtransverse mo-mentum(withmagnitudeEmissT ),whichintheW±-bosonanalysis actsasa proxyforthe transversemomentum of theneutrino, is definedasthenegative of theglobalvector sum ofall identified physics objects (electrons, muons, jets) as well as specific “soft terms”accountingforunclassifiedsofttracksandcalorimeter en-ergyclusters.
The event selection for the W±-boson signature requires ex-actly one identified electron or muon. The event is required to have Emiss
T >25 GeV, and the transverse mass of the W± bo-son calculatedusing themissing transversemomentum vector is requiredto satisfy mT>50 GeV. In order forthe W±-boson se-lectionto be consistent withthe missing transverse momentum reconstruction methodology, an overlap removalalgorithm is ap-plied to the selection for events with jets and leptons found at adistance of R=( η)2+ ( φ)2<0.4 of each other, remov-ing eitherone or the other object. Afterthe full W→ ν selec-tion,a total of 462,950 W±-boson candidates (256,858 W+ and 206,092 W−) pass all requirements in the electronchannel, and 475,208 W±-boson candidates (266,592 W+ and 208,616 W−) passtherequirementsinthemuonchannel.
Eventscontaining a Z -bosoncandidate areselected by requir-ing exactly two selected leptons of the same flavour but of
op-posite charge with invariant mass of 66<m <116 GeV. No
overlap removal is applied in the Z -boson analysis, as missing transverse momentumis not requiredinthe selection. A totalof 35,009 candidates pass all requirements in the electron channel and44,898 candidatesinthemuonchannel.
5. Evaluationofbackgrounds
Contributionsfromtheelectroweak(single-bosonanddiboson) andtop-quark(single-topandtop-quarkpair) componentsof the backgroundareestimatedfromtheMonteCarlosamplesdescribed earlier.The W→τ ν and Z→τ τ processeswiththesubsequent leptonic decayofthe τ are treatedasbackground.The dominant contributions, givenas percentagesof the totalnumber of simu-lated events passing the signal selection in each analysis, are as follows: the W →τ ν and top-quark production contribute ap-proximately 2% and1%, respectively, in the W±-boson analyses, the Z→e+e−and Z→μ+μ− processescontribute1%and5%in
W→eνandW→μν,respectively,whilethetotalbackgroundin
Z→ +−isapproximately0.5%,dominatedbytt production(the sumofallelectroweakbackgroundsis0.2%).
Eventsinvolvingsemileptonicdecaysofheavy quarks,hadrons misidentified as leptons, and, in the case of the electron chan-nel,electronsfromphotonconversions(allreferredto collectively as “multijet events”) are a sizeable source of background in the
W±-bosonanalysis.Themultijetbackgroundinthe Z -boson anal-ysis is estimated from simulation to be < 0.1% and is therefore neglected.
Themultijetcontributiontotheelectronandmuonchannelsof the W±-bosonanalysisisestimatedwitha data-drivenapproach, performing maximum-likelihood fits on the data with template distributions to exploit the discriminating power between signal and background in certain kinematic distributions. The discrimi-nant variables used in the multijet evaluation are mT, EmissT , p
T, and φ betweenthe lepton and transverse missingmomentum. Twofitregionsareusedtoextractthemultijetnormalisation.The first fit region is defined as the full event selection but remov-ing the mT requirement, and the second one is defined as the full eventselection but removing the Emiss
T requirement. Several multijet-enricheddatasamples(multijettemplates)arebuiltfrom eventspassingallselectionrequirementsineachfitregionexcept lepton isolation. Mutually exclusive requirements (“intervals”) in eithertracking- orcalorimeter-basedisolationvariablesarechosen to createstatisticallyindependentmultijet templates. These sam-plesaredesignedtobeprogressivelyclosertothesignal-candidate selection by fixing one of the isolation criteria to that of the signal region and varying the other one; four such samples are builtforeachisolation type intheelectronchannel andfour(for tracking-basedisolation)orsix(forcalorimeter-basedisolation)in themuonchannel.Templatesaresimilarlyconstructedfrom simu-lationforW±signalandelectroweakandtop-quarkbackgrounds, to account for potential contaminationsin the multijet template. Foreachisolation interval,the normalisationofthemultijet tem-plate is extracted with a maximum-likelihood fit to the data in the two fit regions and separately for each one ofthe discrimi-nantvariables andchargedleptonsamples.Ineachfitregion,the normalisation of the signal template derived from simulation is left free to float while the remaining background templates are normalisedtotheir expectedvalues,basedonthemeasured inte-grated luminosity and the predictedcross sections (but are per-mittedtovarywithin5%oftheirexpectedvalues,asdescribed in Section3).Itwasverifiedthatthevalueofthesignalnormalisation extractedfromthisfithasnosignificantimpactonthemultijet es-timate.
Fig. 1. Thenumberofmultijeteventsversustheisolationvariableforthe W→eν(left)and W→μν(right)analysisisshown.Theplotsillustratethemultijet-evaluation methodologyforthe W+analysis.Theresultsobtainedfortwoofthefourdiscriminantvariablesusedtoevaluatethemultijetyieldsareshownforbothtypesofisolation: mT(circles)and p
T(squares)withcalorimeter-basedisolationand mT(triangles)and pT(stars)withtrack-basedisolation.Openmarkersrepresenttheyieldsobtainedwith the EmissT fitregionwhileclosedmarkersarethosewiththe mTfitregion.Thepointsrepresenttheextractedmultijetfractionfromthefitofthevariables,intheisolation intervalsrepresentedonthe x-axis forthetemplateselection.Thelinesrepresentthelinearextrapolationofthepointstothesignalregion.Thedefinitionofthesignalregion is pTandisolation-flavourdependentbutcorrespondsapproximatelytotheregionofisolationbelow0.1intheseplots.Theerrorbarineachbinrepresentstheuncertainty fromthefitofthevariablerescaledbythesquarerootofthereducedχ2ofthefit.
Table 1
Relativesystematicuncertainties(%)inthecorrectionfactors C in thedifferentchannels.
δC/C [%] Z→e+e− W+→e+ν W−→e−ν Z→μ+μ− W+→μ+ν W−→μ−ν
Lepton trigger 0.1 0.3 0.3 0.2 0.6 0.6
Lepton reconstruction, identification 0.9 0.5 0.6 0.9 0.4 0.4
Lepton isolation 0.3 0.1 0.1 0.5 0.3 0.3
Lepton scale and resolution 0.2 0.4 0.4 0.1 0.1 0.1
Charge identification 0.1 0.1 0.1 – – –
JES and JER – 1.7 1.7 – 1.6 1.7
Emiss
T – 0.1 0.1 – 0.1 0.1
Pile-up modelling <0.1 0.4 0.3 <0.1 0.2 0.2
PDF 0.1 0.1 0.1 <0.1 0.1 0.1
Total 1.0 1.9 1.9 1.1 1.8 1.8
Themultijetbackgroundeventyieldineachregion isthen es-timated from this normalisation together with the signal-region requirement ofeither mT>50 GeV, or EmissT >25 GeV. For each discriminant variable, and separately for calorimeter- and track-basedisolation andfor each fitregion,the estimatesobtainedin the isolation intervalsare used to build a linear extrapolationto theisolationselectionusedinthesignalregion.Theextrapolation isperformedassuming that theindividual estimatesare uncorre-lated. Fig. 1illustratesthismultijet-evaluationmethodologyforthe
W+ analysisusingtwo ofthevariables,mT andpT,andforboth fitregions.
Separately for the calorimeter- and track-based isolation vari-ables,andforeachfitregion,anestimateofthebackgroundyield is obtained from a weighted average of the extrapolated values obtainedwiththeindividual discriminantvariables andtheir un-certainties,afterverifyingtheir compatibilitywitha χ2 criterion. The average of the four multijet background estimated fractions found from the track and calorimeter isolation requirements in each fitregion isthen takenasthe nominalmultijetbackground yield in each channel. The uncertainties derived from the linear extrapolations are propagated as systematic uncertainties in the method.A systematicuncertaintyforthechoice ofisolation vari-ableisobtainedfromhalf thedifferencebetweentheaveragesof the calorimeter-basedisolation estimated fractions inthe two fit regions, andthe track-basedaverages. Similarly, a systematic un-certaintyduetotheuseofdifferentfitregionsisevaluatedashalf
thedifferenceoftheaveragesobtainedfromthedifferenttypesof isolationinthetwoseparatefitregions.Inaddition,theimpactof variations ofthejet-energy scaleonthe signaltemplate isadded inquadraturetothemultijetsystematicuncertainty.
The estimatedmultijetbackgroundfractionsof thetotal num-ber ofobserved candidateeventsare 8% and10% inthe electron
W+andW−channelsand3.5%and4%inthemuonW+andW−
channels. Thecorresponding relativeuncertainties rangefrom ap-proximately 20% to30%forthe muonandelectronchannels, and aresimilarforboththepositivelyandnegativelychargedsamples. 6. Evaluationofsystematicuncertainties
Theexperimentalsystematicuncertaintiesinthemeasurements ofthecrosssectionsenterviatheevaluationofthecorrection fac-torandtheluminosityinthedenominator ofEq.(1),andthrough the estimation ofthe background subtracted from the candidate eventsinitsnumerator.
The sources of systematic uncertainties in the correction fac-tors C , summarisedin Table 1,are asfollows.Trigger: The lepton triggerefficiencyisestimatedinsimulation,withadedicated data-drivenanalysisperformedtoobtainthesimulation-to-datatrigger correctionfactorsandthecorrespondinguncertainties. Reconstruc-tion,Identification, andIsolation: The lepton selection efficiencies as determined fromsimulation are corrected with simulation-to-data correction factors andtheir associateduncertainties [41,42].
Fig. 2. Transversemassdistributionsfromthe W→eν and W→μν selections(top)anddileptonmassdistributionsfromthe Z→e+e− and Z→μ+μ− selections (bottom).Thepredictedsignaldistributionsarenormalisedtothemeasuredcrosssectionsaspresentedinthispaper.Theshadedbandsinthehistogramsencompassthe uncertaintiesdescribedinTable 1.Inadditiontotheseuncertaintiesinthecorrectionfactors,theuncertaintiesintheevaluationofthemultijetbackgroundinthe W±-boson analysisareincludedintheshadedbands.
Energy,MomentumScale/Resolution: Uncertaintiesinthelepton cal-ibrations are applied as they can cause a change of acceptance because ofmigration of events across the pT threshold andm
boundaries.ChargeIdentification: Electroncharge misidentification mayoccur when electrons radiate early in the detector and the resulting photonssubsequently convert and are reconstructed as high pT tracks. A particle with reconstructed charge opposite to theparentelectron maythen accidentallybe associatedwiththe calorimetercluster. Theeffectofelectronshavingtheir charge re-constructedwrongly isstudiedusing acontrol sample of Z→ee
eventsin which both electrons are reconstructed withthe same chargeandisfoundtobewelldescribed bytheMonteCarlo sim-ulation, within the statistical uncertainty of the control sample. Anuncertaintyisassessedto coveranysmallresidualdifferences betweendataand simulation.The probability of charge misiden-tification isnegligible inthe muon channel. Jet-Energy Scale/Reso-lution(JESandJER): The corresponding uncertainties, described in Ref. [46], are propagated to the calculation ofthe missing trans-versemomentum.Emiss
T : Uncertaintiesinthesoftcomponentofthe
EmissT scale andresolutionevaluated asdescribed inRef. [47] are included.Pile-up: Incorrectmodellingofpile-upeffectscanleadto acceptance changes and is accountedfor with dedicated studies.
PDF: TheimpactofPDFeigenvectorvariationsispropagatedtothe correctionfactor.
Inthe Z -bosonchannel, thesystematicuncertainties fromthe
background evaluation contribute negligibly to the experimental cross-section uncertainty. Thisis not the casefor the W±-boson channel;the multijetbackground evaluationresultsin uncertain-tiesofupto3.4%onthecross-sectionmeasurements inthe elec-tronchannelandupto1.4%inthemuonchannel.
The measurementof theintegrated luminosityhas a2.1% un-certainty,whichisderived,followingamethodologysimilartothat detailedinRef.[48],fromacalibrationoftheluminosityscale
us-ing x– y beam-separation scansperformedin August 2015. Apart
from the determination of the luminosity, the dominant exper-imental systematic uncertainties in the cross-section evaluations arethejet-energyscale/resolutionandthemultijetbackgroundfor theW±-bosonmeasurementswhiletheyareleptonreconstruction andidentificationefficienciesforthe Z -bosonmeasurements.
Table 2
Thefiducialandtotalcrosssectionsfor W+, W−,and Z bosons intheelectronandmuonchannels.Theobservednumbersofsignalevents afterbackgroundsubtractionareshownforeachchannel,alongwiththecorrectionfactors C andthegeometricalacceptancecorrection factors A (bothgivenwiththetotaluncertaintyonly).Theluminosityuncertaintiesinthemeasurednumberofsignaleventscorrespond tothosefromtheelectroweakandtop-quarkbackgroundsestimatedfromsimulation.
W+ W− Z
Electron channel (value±stat±syst±lumi)
Signal events 228060±510±4920±200 177890±450±6110±180 34865±187±7±3 Correction C 0.602±0.012 0.614±0.012 0.552+−00..006005 σfid[nb] 4 .68±0.01±0.14±0.10 3.58±0.01±0.14±0.08 0.781±0.004±0.008±0.016 Acceptance A 0.383±0.007 0.398±0.007 0.393±0.007 σtot[nb] 12.23±0.03±0.42±0.27 9.00±0.02±0.39±0.20 1.987±0.011±0.041±0.042 Muon channel (value±stat±syst±lumi)
Signal events 237720±520±2210±410 183180±460±2520±360 44706±212±9±4 Correction C 0.653±0.012 0.650±0.012 0.711±0.008 σfid[nb] 4.50±0.01±0.09±0.10 3.48±0.01±0.08±0.08 0.777±0.004±0.008±0.016 Acceptance A 0.383±0.007 0.398±0.007 0.393±0.007 σtot[nb] 11 .75±0.03±0.33±0.27 8.75±0.02±0.25±0.20 1.977±0.009±0.041±0.042
Fig. 3. Ratiooftheelectron- andmuon-channel W±and Z -boson production fidu-cialcrosssections,comparedtotheexpectedvaluesoftheStandardModelof(1,1)
(neglectingmasseffectsthatcontributeatalevelbelow10−5)andprevious experi-mentalverificationsofleptonuniversalityforon-shell W±and Z bosons, shownas PDGaveragebands[49,50].ThePDGaveragevaluesandtheresultareshownwith totaluncertainties.
7. Results
ThemTandmdistributionsafterthefinalselectionareshown
in Fig. 2 for the W→eν, W→μν and Z→e+e−, and Z →
μ+μ− channels, respectively, for the data compared to the pre-dictions, normalised to the measured cross section. All elements necessarytocalculatethecrosssectionsforW+,W−andZ -boson
productionanddecayintheelectronandmuonchannelsare sum-marisedin Table 2.Thederivedfiducialandtotalcrosssectionsare alsopresentedinthistable,alongwiththeirstatistical,systematic, andluminosityuncertainties.
Theratiosofthefiducialelectronandmuonchannel measure-ments in the W± (RW± =σWfid±→eν/σ
fid
W±→μν ) and the Z -boson
(RZ=σZfid→e+e−/σ fid
Z→μ+μ−)channels,evaluatedtakingintoaccount
correlations in the systematicuncertainties, are shown in Fig. 3. SincetheseresultsagreewellwithStandardModelexpectationsof lepton universality, a simultaneous combinationof the W+, W−
andZ -bosonfiducialcrosssectionsusingtheHERAverager
pro-gram[51,52]isperformed.
Thecombinationuses theindividual sourcesofthe systematic uncertainties,asshownin Table 1,inaddition touncertainties in the background evaluations. Sources corresponding to lepton re-constructionandidentificationareuncorrelatedbetweenthe elec-tronandmuonchannels.Somesources,suchasJES,JER,Emiss
T and
multijet background, only affect W±-boson measurements. The correlation model used forcombining the multijet W+ and W−
uncertaintiesineachleptonchannelisdefinedby:
δ(W±)2= δ(W+)2+ δ(W−)2+2ρδ(W+)δ(W−), (2)
performed separately for each source of systematic uncertainty considered forthisbackground.Allsuch uncertainties are consid-ered to be uncorrelated between the electron and muon chan-nels except that of thejet-energy-scale variation. Thecorrelation coefficient, ρ, is obtainedfrom theuncertainties evaluated sepa-rately for the W+ and W− channels (δ(W+), δ(W−)), and re-peating the multijetbackground extraction without selecting the final-statecharge (δ(W±)).Thecorrelationsofthesystematic un-certaintiesvaryfrom0.2to1(fullycorrelated),depending onthe lepton channel and type of uncertainty. The common normali-sation uncertainty due to the luminosity calibration is excluded fromthecombinationprocedureandappliedseparatelytothe re-sult.
The combination yields a χ2/N
d.o.f.=3.0/3, indicating excel-lentcompatibility ofthe measurements. Table 3 givesthe result-ing combined cross sections.There is a reduction of uncertainty comparedtoindividualelectronandmuonchannelmeasurements sincemanyofthesystematicuncertaintysourcesareuncorrelated. The combinedfiducial cross sections are extrapolatedto the full phase space usingthe acceptance factors of Table 2. These total cross sections are reportedin Table 3. The central values of the fiducial and total cross-section predictions, as described in Sec-tion 2, are also provided in Table 3. The statisticaluncertainties resultingfromtheevaluationofthesepredictionsarenegligible.
The combinedfiducialcrosssectionsarecomparedin Fig. 4to thepredictions,whicharecalculatedusingdifferentPDF sets.The measurementsagreewellwiththepredictionsandthe experimen-talprecisioniscomparabletothePDFuncertainties.
Ratiosofthemeasuredcrosssectionsbenefitfromthe cancella-tionofsomeexperimentaluncertainties.TheratiosofW+toW−
andW±to Z -bosonproduction,measuredbytheATLAS,CMS,and
LHCbcollaborationsinthepast [24,53–56],provedtobepowerful tools to constrain PDF fits. The ratio of W+ to W−-boson cross sectionsismostlysensitivetothedifferenceofuvanddv valence-quark distributions atlowBjorken-x, whilethe ratioofW± to Z
constrainsthestrange-quarkdistribution[18].
The systematic uncertainties of the ratio measurements are largely uncorrelated between the electron and muon channels, apartfromthecommonluminosity uncertainty.However,thereis a strong correlation between W+ and W−-bosonmeasurements
Table 3
Themeasuredfiducialσfidandtotalσtotcrosssectionsforthecombinedelectronandmuonchannelsof W−, W+, W±,and Z -boson productionandthefiducialratios W+/W−and W±/Z . AlsoshownarethepredictedvaluesasdiscussedinSection2.The CT14nnloPDF isusedforthepredictions.Inthesecondsetofnumericalcolumns,theerrorlabelledas“other”representstheuncertaintyinαSandin thebeamenergy.
Channel
Measuredcrosssection×BR(W→ ν, Z→ )[nb] (value±stat±syst±lumi)
Predictedcrosssection×BR(W→ ν, Z→ )[nb] (value±PDF±scale±other)
Fiducial Total Fiducial Total
W− 3.50±0.01±0.07±0.07 8.79±0.02±0.24±0.18 3.40−+00..0911±0.04±0.06 8.54+ 0.21 −0.24±0.11±0.12 W+ 4.53±0.01±0.09±0.10 11.83±0.02±0.32±0.25 4.42+0.13 −0.14±0.05±0.08 11.54+ 0.32 −0.31±0.15±0.16 W± 8.03±0.01±0.16±0.17 20.64±0.02±0.55±0.43 7.82+0.21 −0.25±0.09±0.13 20.08+ 0.53 −0.54±0.26±0.28 Z 0.779±0.003±0.006±0.016 1.981±0.007±0.038±0.042 0.74+−00..0203±0.01±0.01 1.89±0.05±0.03±0.03
Measured ratio (value±stat±syst) Predicted ratio (value±PDF)
W+/W− 1.295±0.003±0.010 – 1.30±0.01 –
W±/Z 10.31±0.04±0.20 – 10.54±0.12 –
Fig. 4. RatioofthepredictedtomeasuredfiducialcrosssectionforthecombinedelectronandmuonchannelsusingvariousPDFs.Theinner(outer)bandcorrespondstothe experimentaluncertaintywithout(with)theluminosityuncertainty.TheinnererrorbarofthepredictionsrepresentsthePDFuncertaintywhiletheoutererrorbarincludes thesuminquadratureofallothersystematicuncertainties.
Fig. 5. Ratios(redline)of W+to W− boson(left)and W±to Z boson (right)combinedproductioncrosssectionsinthefiducialregioncomparedtopredictionsbased ondifferentPDFsets.Theinner(yellow)shadedbandcorrespondstothestatisticaluncertaintywhiletheouter(green)bandshowsstatisticalandsystematicuncertainties addedinquadrature.ThetheorypredictionsaregivenwithonlythecorrespondingPDFuncertaintiesshownaserrorbars.(Forinterpretationofthereferencestocolourin thisfigurelegend,thereaderisreferredtothewebversionofthisarticle.)
andbetween the W± and Z -boson results for the same-flavour measurement.Theresultsforthemeasured W+/W− and W±/Z
ratiosof fiducialproductioncross sectionsinthe combined elec-tronandmuon channelsaswell asthecorresponding predictions asdescribed in Section 2 are given inTable 3 andpresented in Fig. 5. The dominant components of the systematic uncertainty
in the W±/Z ratio are from both the multijet background and
the jet-energy scale/resolution while that of the W+/W− ratio is from the uncorrelated part of the multijet background uncer-tainty.FortheratiosRW+/W−=σWfid+/σ
fid W− andRW/Z=σ fid W±/σ fid Z , several predictions agree within quoted uncertainties, although all predictions are above the central value for the data in both cases.
8. Conclusion
MeasurementswiththeATLASdetectorattheLHCoftheW→
ν andZ→ +−productioncrosssectionsbasedon938,158and 79,907candidates,respectively,arepresented.Theseresults corre-spond to a total integratedluminosity ofapproximately 81 pb−1 ofproton–protoncollisions at√s=13 TeV, thehighest centre-of-massenergyeveravailablefromacollider.ThesizeoftheW±and
Z -boson production cross sections at this LHC Run-2
centre-of-massenergyareenhancedbyafactorofnearlytwofromthoseat √
s=7 TeV and 8 TeV inRun-1.Themeasurementsofthefiducial crosssectionsofW+,W−,andZ -bosonproductionaremade sep-aratelyintheelectronandmuondecaychannelsandarefoundto
beconsistentbetweenthetwochannels.Thedatasetsforelectron andmuondecaychannelsarethencombinedusingamethodology whichaccountsforthecorrelationsoftheexperimentalsystematic uncertainties. The measured fiducial andtotal cross sections are found toagree withtheoretical calculationsbasedon NNLO QCD withNLO EW corrections. These measured cross sectionshave a globalluminosityuncertaintyof2.1%,whiletheirremaining exper-imentaluncertaintiesinthe W± and Z -bosonchannelsarefound to be just under 3% and 1%, respectively. The measurements of cross-section ratios benefit fromthe cancellation of some exper-imentaluncertainties,andarepowerfultoolstoconstrainPDFfits. Inparticular,the fiducialcross-sectionratioof W+ to W−, mea-suredwithanuncertaintyof0.8%,isabletodiscriminateamongst thevarious PDF predictionspresented.Theseresultsforma basis forfurther testsof perturbative QCD and exploration ofthe par-toniccontentoftheproton.
Acknowledgements
We thankCERN for the very successfuloperation of theLHC, aswell asthe support stafffrom ourinstitutions without whom ATLAScouldnotbeoperatedefficiently.
WeacknowledgethesupportofANPCyT,Argentina;YerPhI, Ar-menia;ARC,Australia;BMWFW andFWF,Austria;ANAS, Azerbai-jan;SSTC,Belarus; CNPqandFAPESP,Brazil;NSERC, NRCandCFI, Canada;CERN;CONICYT,Chile;CAS,MOSTandNSFC,China; COL-CIENCIAS, Colombia; MSMT CR, MPO CR andVSC CR, Czech Re-public; DNRF andDNSRC, Denmark; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece;RGC,HongKongSAR,China;ISF,I-COREandBenoziyo Cen-ter, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland;FCT,Portugal;MNE/IFA,Romania; MESofRussiaandNRC KI,RussianFederation;JINR;MESTD,Serbia;MSSR,Slovakia;ARRS and MIZŠ, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden;SERI, SNSF and Cantons of BernandGeneva,Switzerland;MOST,Taiwan;TAEK,Turkey;STFC, United Kingdom; DOE and NSF, United States. In addition, indi-vidual groups and members have received support from BCKDF, the Canada Council, Canarie, CRC, Compute Canada, FQRNT, and theOntarioInnovationTrust,Canada; EPLANET,ERC,FP7,Horizon 2020 and Marie Skłodowska-Curie Actions, European Union; In-vestissementsd’AvenirLabexandIdex,ANR,RégionAuvergneand FondationPartagerleSavoir,France;DFGandAvHFoundation, Ger-many;Herakleitos,ThalesandAristeiaprogrammesco-financedby EU-ESFandtheGreekNSRF;BSF,GIFandMinerva,Israel;BRF, Nor-way;Generalitat de Catalunya, Generalitat Valenciana, Spain;the RoyalSocietyandLeverhulmeTrust,UnitedKingdom.
The crucial computingsupport fromall WLCG partners is ac-knowledged 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) andBNL(USA)andintheTier-2 facilitiesworldwide.
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H.P. Beck18,g,K. Becker121, M. Becker85, M. Beckingham170, C. Becot111, A.J. Beddall20e, A. Beddall20b, V.A. Bednyakov67,M. Bedognetti108, C.P. Bee149,L.J. Beemster108, T.A. Beermann32, M. Begel27,
M. Bellomo88,K. Belotskiy99, O. Beltramello32,N.L. Belyaev99, O. Benary154,D. Benchekroun136a, M. Bender101, K. Bendtz147a,147b,N. Benekos10, Y. Benhammou154,E. Benhar Noccioli176, J. Benitez65, D.P. Benjamin47, J.R. Bensinger25, S. Bentvelsen108,L. Beresford121,M. Beretta49, D. Berge108,
E. Bergeaas Kuutmann165,N. Berger5,J. Beringer16, S. Berlendis57, N.R. Bernard88,C. Bernius111, F.U. Bernlochner23,T. Berry79,P. Berta130, C. Bertella85,G. Bertoli147a,147b, F. Bertolucci125a,125b,
I.A. Bertram74,C. Bertsche44,D. Bertsche114, G.J. Besjes38,O. Bessidskaia Bylund147a,147b,M. Bessner44, N. Besson137, C. Betancourt50, S. Bethke102, A.J. Bevan78, W. Bhimji16, R.M. Bianchi126, L. Bianchini25, M. Bianco32, O. Biebel101, D. Biedermann17, R. Bielski86,N.V. Biesuz125a,125b,M. Biglietti135a,
J. Bilbao De Mendizabal51,H. Bilokon49, M. Bindi56,S. Binet118,A. Bingul20b,C. Bini133a,133b, S. Biondi22a,22b,D.M. Bjergaard47, C.W. Black151, J.E. Black144,K.M. Black24,D. Blackburn139, R.E. Blair6, J.-B. Blanchard137,J.E. Blanco79, T. Blazek145a,I. Bloch44, C. Blocker25,W. Blum85,∗, U. Blumenschein56,S. Blunier34a,G.J. Bobbink108, V.S. Bobrovnikov110,c,S.S. Bocchetta83, A. Bocci47, C. Bock101, M. Boehler50,D. Boerner175, J.A. Bogaerts32, D. Bogavac14,A.G. Bogdanchikov110,
C. Bohm147a,V. Boisvert79, P. Bokan14, T. Bold40a,A.S. Boldyrev164a,164c,M. Bomben82,M. Bona78, M. Boonekamp137, A. Borisov131,G. Borissov74,J. Bortfeldt101,D. Bortoletto121,V. Bortolotto62a,62b,62c, K. Bos108,D. Boscherini22a,M. Bosman13,J.D. Bossio Sola29,J. Boudreau126, J. Bouffard2,
E.V. Bouhova-Thacker74,D. Boumediene36,C. Bourdarios118,S.K. Boutle55,A. Boveia32, J. Boyd32, I.R. Boyko67,J. Bracinik19, A. Brandt8, G. Brandt56, O. Brandt60a, U. Bratzler157,B. Brau88, J.E. Brau117, H.M. Braun175,∗,W.D. Breaden Madden55, K. Brendlinger123, A.J. Brennan90,L. Brenner108,
R. Brenner165,S. Bressler172,T.M. Bristow48, D. Britton55, D. Britzger44,F.M. Brochu30, I. Brock23, R. Brock92,G. Brooijmans37,T. Brooks79, W.K. Brooks34b, J. Brosamer16, E. Brost117, J.H Broughton19, P.A. Bruckman de Renstrom41,D. Bruncko145b,R. Bruneliere50,A. Bruni22a, G. Bruni22a, BH Brunt30, M. Bruschi22a, N. Bruscino23, P. Bryant33, L. Bryngemark83, T. Buanes15,Q. Buat143,P. Buchholz142, A.G. Buckley55, I.A. Budagov67,F. Buehrer50, M.K. Bugge120, O. Bulekov99, D. Bullock8,H. Burckhart32, S. Burdin76, C.D. Burgard50, B. Burghgrave109,K. Burka41,S. Burke132,I. Burmeister45, E. Busato36, D. Büscher50, V. Büscher85,P. Bussey55,J.M. Butler24, C.M. Buttar55,J.M. Butterworth80,P. Butti108, W. Buttinger27,A. Buzatu55,A.R. Buzykaev110,c, S. Cabrera Urbán167, D. Caforio129, V.M. Cairo39a,39b, O. Cakir4a, N. Calace51, P. Calafiura16,A. Calandri87, G. Calderini82,P. Calfayan101, L.P. Caloba26a, D. Calvet36, S. Calvet36,T.P. Calvet87,R. Camacho Toro33,S. Camarda32, P. Camarri134a,134b, D. Cameron120,R. Caminal Armadans166,C. Camincher57,S. Campana32, M. Campanelli80,
A. Camplani93a,93b, A. Campoverde149,V. Canale105a,105b, A. Canepa160a,M. Cano Bret35e,J. Cantero115, R. Cantrill127a,T. Cao42, M.D.M. Capeans Garrido32,I. Caprini28b,M. Caprini28b, M. Capua39a,39b,
R. Caputo85, R.M. Carbone37, R. Cardarelli134a, F. Cardillo50,T. Carli32,G. Carlino105a,
L. Carminati93a,93b,S. Caron107,E. Carquin34b,G.D. Carrillo-Montoya32,J.R. Carter30,J. Carvalho127a,127c, D. Casadei19,M.P. Casado13,h,M. Casolino13, D.W. Casper163,E. Castaneda-Miranda146a, R. Castelijn108, A. Castelli108,V. Castillo Gimenez167,N.F. Castro127a,i,A. Catinaccio32, J.R. Catmore120, A. Cattai32, J. Caudron85, V. Cavaliere166,E. Cavallaro13,D. Cavalli93a,M. Cavalli-Sforza13,V. Cavasinni125a,125b, F. Ceradini135a,135b, L. Cerda Alberich167,B.C. Cerio47,A.S. Cerqueira26b,A. Cerri150,L. Cerrito78, F. Cerutti16, M. Cerv32,A. Cervelli18, S.A. Cetin20d,A. Chafaq136a, D. Chakraborty109, I. Chalupkova130, S.K. Chan59, Y.L. Chan62a, P. Chang166,J.D. Chapman30,D.G. Charlton19, A. Chatterjee51,C.C. Chau159, C.A. Chavez Barajas150,S. Che112, S. Cheatham74, A. Chegwidden92,S. Chekanov6, S.V. Chekulaev160a, G.A. Chelkov67,j,M.A. Chelstowska91, C. Chen66,H. Chen27, K. Chen149,S. Chen35c,S. Chen156, X. Chen35f,Y. Chen69,H.C. Cheng91, H.J Cheng35a, Y. Cheng33, A. Cheplakov67, E. Cheremushkina131, R. Cherkaoui El Moursli136e,V. Chernyatin27,∗,E. Cheu7, L. Chevalier137,V. Chiarella49,
G. Chiarelli125a,125b,G. Chiodini75a,A.S. Chisholm19, A. Chitan28b, M.V. Chizhov67, K. Choi63, A.R. Chomont36,S. Chouridou9, B.K.B. Chow101, V. Christodoulou80, D. Chromek-Burckhart32, J. Chudoba128, A.J. Chuinard89, J.J. Chwastowski41, L. Chytka116,G. Ciapetti133a,133b,A.K. Ciftci4a, D. Cinca55,V. Cindro77,I.A. Cioara23,A. Ciocio16, F. Cirotto105a,105b, Z.H. Citron172,M. Citterio93a, M. Ciubancan28b,A. Clark51,B.L. Clark59, M.R. Clark37,P.J. Clark48,R.N. Clarke16, C. Clement147a,147b, Y. Coadou87, M. Cobal164a,164c,A. Coccaro51,J. Cochran66, L. Coffey25,L. Colasurdo107,B. Cole37, A.P. Colijn108,J. Collot57,T. Colombo32, G. Compostella102, P. Conde Muiño127a,127b, E. Coniavitis50, S.H. Connell146b, I.A. Connelly79, V. Consorti50,S. Constantinescu28b,G. Conti32,F. Conventi105a,k,
M. Cooke16,B.D. Cooper80,A.M. Cooper-Sarkar121, K.J.R. Cormier159,T. Cornelissen175, M. Corradi133a,133b,F. Corriveau89,l, A. Corso-Radu163, A. Cortes-Gonzalez13, G. Cortiana102, G. Costa93a,M.J. Costa167,D. Costanzo140,G. Cottin30, G. Cowan79,B.E. Cox86,K. Cranmer111, S.J. Crawley55, G. Cree31, S. Crépé-Renaudin57,F. Crescioli82, W.A. Cribbs147a,147b,
M. Crispin Ortuzar121,M. Cristinziani23, V. Croft107,G. Crosetti39a,39b, T. Cuhadar Donszelmann140,
J. Cummings176,M. Curatolo49, J. Cúth85,C. Cuthbert151, H. Czirr142,P. Czodrowski3,G. D’amen22a,22b, S. D’Auria55, M. D’Onofrio76,M.J. Da Cunha Sargedas De Sousa127a,127b,C. Da Via86,W. Dabrowski40a, T. Dado145a,T. Dai91, O. Dale15,F. Dallaire96, C. Dallapiccola88,M. Dam38,J.R. Dandoy33,N.P. Dang50, A.C. Daniells19,N.S. Dann86,M. Danninger168, M. Dano Hoffmann137,V. Dao50,G. Darbo52a,
S. Darmora8, J. Dassoulas3,A. Dattagupta63, W. Davey23,C. David169,T. Davidek130, M. Davies154, P. Davison80, E. Dawe90, I. Dawson140,R.K. Daya-Ishmukhametova88,K. De8, R. de Asmundis105a, A. De Benedetti114,S. De Castro22a,22b,S. De Cecco82, N. De Groot107,P. de Jong108, H. De la Torre84, F. De Lorenzi66,A. De Maria56, D. De Pedis133a, A. De Salvo133a,U. De Sanctis150,A. De Santo150, J.B. De Vivie De Regie118,W.J. Dearnaley74, R. Debbe27,C. Debenedetti138,D.V. Dedovich67,
N. Dehghanian3, I. Deigaard108,M. Del Gaudio39a,39b,J. Del Peso84, T. Del Prete125a,125b,D. Delgove118, F. Deliot137,C.M. Delitzsch51, M. Deliyergiyev77, A. Dell’Acqua32,L. Dell’Asta24,M. Dell’Orso125a,125b, M. Della Pietra105a,k,D. della Volpe51,M. Delmastro5,P.A. Delsart57, C. Deluca108, D.A. DeMarco159, S. Demers176, M. Demichev67,A. Demilly82,S.P. Denisov131, D. Denysiuk137,D. Derendarz41,
J.E. Derkaoui136d,F. Derue82, P. Dervan76,K. Desch23, C. Deterre44, K. Dette45, P.O. Deviveiros32, A. Dewhurst132,S. Dhaliwal25,A. Di Ciaccio134a,134b,L. Di Ciaccio5,W.K. Di Clemente123,
C. Di Donato133a,133b, A. Di Girolamo32, B. Di Girolamo32, B. Di Micco135a,135b, R. Di Nardo32, A. Di Simone50,R. Di Sipio159, D. Di Valentino31,C. Diaconu87,M. Diamond159, F.A. Dias48, M.A. Diaz34a, E.B. Diehl91,J. Dietrich17,S. Diglio87, A. Dimitrievska14,J. Dingfelder23, P. Dita28b, S. Dita28b, F. Dittus32, F. Djama87, T. Djobava53b, J.I. Djuvsland60a,M.A.B. do Vale26c,D. Dobos32, M. Dobre28b,C. Doglioni83, T. Dohmae156,J. Dolejsi130,Z. Dolezal130, B.A. Dolgoshein99,∗,
M. Donadelli26d,S. Donati125a,125b,P. Dondero122a,122b, J. Donini36,J. Dopke132, A. Doria105a,
M.T. Dova73,A.T. Doyle55, E. Drechsler56, M. Dris10, Y. Du35d, J. Duarte-Campderros154,E. Duchovni172, G. Duckeck101, O.A. Ducu96,m, D. Duda108,A. Dudarev32,L. Duflot118, L. Duguid79, M. Dührssen32, M. Dumancic172,M. Dunford60a,H. Duran Yildiz4a, M. Düren54,A. Durglishvili53b, D. Duschinger46, B. Dutta44, M. Dyndal40a,C. Eckardt44,K.M. Ecker102,R.C. Edgar91,N.C. Edwards48,T. Eifert32, G. Eigen15,K. Einsweiler16,T. Ekelof165, M. El Kacimi136c, V. Ellajosyula87, M. Ellert165,S. Elles5, F. Ellinghaus175, A.A. Elliot169,N. Ellis32, J. Elmsheuser27,M. Elsing32,D. Emeliyanov132, Y. Enari156, O.C. Endner85,M. Endo119,J.S. Ennis170, J. Erdmann45,A. Ereditato18,G. Ernis175, J. Ernst2,M. Ernst27, S. Errede166,E. Ertel85,M. Escalier118, H. Esch45,C. Escobar126, B. Esposito49, A.I. Etienvre137,
E. Etzion154,H. Evans63, A. Ezhilov124,F. Fabbri22a,22b, L. Fabbri22a,22b, G. Facini33,
R.M. Fakhrutdinov131, S. Falciano133a,R.J. Falla80, J. Faltova130,Y. Fang35a, M. Fanti93a,93b, A. Farbin8, A. Farilla135a, C. Farina126, T. Farooque13, S. Farrell16,S.M. Farrington170,P. Farthouat32, F. Fassi136e, P. Fassnacht32,D. Fassouliotis9,M. Faucci Giannelli79,A. Favareto52a,52b,W.J. Fawcett121,L. Fayard118, O.L. Fedin124,n, W. Fedorko168,S. Feigl120, L. Feligioni87,C. Feng35d,E.J. Feng32, H. Feng91,
A.B. Fenyuk131,L. Feremenga8,P. Fernandez Martinez167, S. Fernandez Perez13, J. Ferrando55, A. Ferrari165,P. Ferrari108, R. Ferrari122a, D.E. Ferreira de Lima60b, A. Ferrer167,D. Ferrere51, C. Ferretti91,A. Ferretto Parodi52a,52b,F. Fiedler85,A. Filipˇciˇc77,M. Filipuzzi44,F. Filthaut107, M. Fincke-Keeler169,K.D. Finelli151, M.C.N. Fiolhais127a,127c,L. Fiorini167, A. Firan42, A. Fischer2, C. Fischer13,J. Fischer175,W.C. Fisher92, N. Flaschel44,I. Fleck142,P. Fleischmann91,G.T. Fletcher140, R.R.M. Fletcher123, T. Flick175, A. Floderus83, L.R. Flores Castillo62a, M.J. Flowerdew102, G.T. Forcolin86, A. Formica137,A. Forti86, A.G. Foster19,D. Fournier118,H. Fox74, S. Fracchia13, P. Francavilla82,
M. Franchini22a,22b,D. Francis32, L. Franconi120, M. Franklin59, M. Frate163,M. Fraternali122a,122b, D. Freeborn80,S.M. Fressard-Batraneanu32,F. Friedrich46, D. Froidevaux32, J.A. Frost121, C. Fukunaga157, E. Fullana Torregrosa85, T. Fusayasu103, J. Fuster167, C. Gabaldon57,O. Gabizon175,A. Gabrielli22a,22b, A. Gabrielli16,G.P. Gach40a, S. Gadatsch32, S. Gadomski51, G. Gagliardi52a,52b, L.G. Gagnon96,
P. Gagnon63, C. Galea107,B. Galhardo127a,127c,E.J. Gallas121, B.J. Gallop132, P. Gallus129,G. Galster38, K.K. Gan112,J. Gao35b,87,Y. Gao48,Y.S. Gao144,f,F.M. Garay Walls48,C. García167,J.E. García Navarro167,
M. Garcia-Sciveres16, R.W. Gardner33, N. Garelli144,V. Garonne120,A. Gascon Bravo44,C. Gatti49, A. Gaudiello52a,52b,G. Gaudio122a,B. Gaur142, L. Gauthier96, I.L. Gavrilenko97,C. Gay168, G. Gaycken23, E.N. Gazis10, Z. Gecse168, C.N.P. Gee132,Ch. Geich-Gimbel23, M.P. Geisler60a,C. Gemme52a,
M.H. Genest57,C. Geng35b,o, S. Gentile133a,133b, S. George79,D. Gerbaudo13,A. Gershon154,
S. Ghasemi142, H. Ghazlane136b, M. Ghneimat23,B. Giacobbe22a,S. Giagu133a,133b, P. Giannetti125a,125b,
B. Gibbard27,S.M. Gibson79,M. Gignac168, M. Gilchriese16, T.P.S. Gillam30,D. Gillberg31,G. Gilles175, D.M. Gingrich3,d, N. Giokaris9,M.P. Giordani164a,164c,F.M. Giorgi22a,F.M. Giorgi17,P.F. Giraud137, P. Giromini59, D. Giugni93a,F. Giuli121, C. Giuliani102,M. Giulini60b,B.K. Gjelsten120, S. Gkaitatzis155, I. Gkialas155,E.L. Gkougkousis118,L.K. Gladilin100,C. Glasman84, J. Glatzer32,P.C.F. Glaysher48, A. Glazov44,M. Goblirsch-Kolb102,J. Godlewski41,S. Goldfarb91,T. Golling51,D. Golubkov131, A. Gomes127a,127b,127d,R. Gonçalo127a,J. Goncalves Pinto Firmino Da Costa137, L. Gonella19,
A. Gongadze67,S. González de la Hoz167, G. Gonzalez Parra13, S. Gonzalez-Sevilla51, L. Goossens32, P.A. Gorbounov98,H.A. Gordon27, I. Gorelov106, B. Gorini32,E. Gorini75a,75b, A. Gorišek77,E. Gornicki41, A.T. Goshaw47, C. Gössling45, M.I. Gostkin67,C.R. Goudet118, D. Goujdami136c,A.G. Goussiou139,
N. Govender146b,E. Gozani153,L. Graber56, I. Grabowska-Bold40a, P.O.J. Gradin57, P. Grafström22a,22b, J. Gramling51,E. Gramstad120,S. Grancagnolo17,V. Gratchev124, H.M. Gray32, E. Graziani135a,
Z.D. Greenwood81,p,C. Grefe23, K. Gregersen80, I.M. Gregor44,P. Grenier144,K. Grevtsov5,J. Griffiths8, A.A. Grillo138,K. Grimm74,S. Grinstein13,q,Ph. Gris36, J.-F. Grivaz118,S. Groh85, J.P. Grohs46,
E. Gross172, J. Grosse-Knetter56,G.C. Grossi81, Z.J. Grout150,L. Guan91,W. Guan173,J. Guenther129, F. Guescini51,D. Guest163,O. Gueta154, E. Guido52a,52b, T. Guillemin5,S. Guindon2,U. Gul55, C. Gumpert32,J. Guo35e,Y. Guo35b,o, S. Gupta121,G. Gustavino133a,133b, P. Gutierrez114,
N.G. Gutierrez Ortiz80, C. Gutschow46, C. Guyot137, C. Gwenlan121, C.B. Gwilliam76, A. Haas111, C. Haber16,H.K. Hadavand8,N. Haddad136e,A. Hadef87, P. Haefner23, S. Hageböck23, Z. Hajduk41, H. Hakobyan177,∗,M. Haleem44, J. Haley115, G. Halladjian92,G.D. Hallewell87, K. Hamacher175, P. Hamal116, K. Hamano169, A. Hamilton146a, G.N. Hamity140, P.G. Hamnett44,L. Han35b,
K. Hanagaki68,r,K. Hanawa156, M. Hance138, B. Haney123,P. Hanke60a,R. Hanna137, J.B. Hansen38, J.D. Hansen38,M.C. Hansen23,P.H. Hansen38,K. Hara161, A.S. Hard173, T. Harenberg175,F. Hariri118, S. Harkusha94,R.D. Harrington48,P.F. Harrison170,F. Hartjes108, N.M. Hartmann101, M. Hasegawa69, Y. Hasegawa141,A. Hasib114,S. Hassani137, S. Haug18, R. Hauser92,L. Hauswald46, M. Havranek128, C.M. Hawkes19, R.J. Hawkings32, D. Hayden92,C.P. Hays121, J.M. Hays78,H.S. Hayward76,
S.J. Haywood132, S.J. Head19, T. Heck85, V. Hedberg83,L. Heelan8, S. Heim123,T. Heim16, B. Heinemann16, J.J. Heinrich101, L. Heinrich111,C. Heinz54, J. Hejbal128,L. Helary24,
S. Hellman147a,147b,C. Helsens32,J. Henderson121, R.C.W. Henderson74,Y. Heng173, S. Henkelmann168, A.M. Henriques Correia32,S. Henrot-Versille118,G.H. Herbert17,Y. Hernández Jiménez167, G. Herten50, R. Hertenberger101, L. Hervas32,G.G. Hesketh80,N.P. Hessey108, J.W. Hetherly42,R. Hickling78,
E. Higón-Rodriguez167,E. Hill169, J.C. Hill30,K.H. Hiller44, S.J. Hillier19, I. Hinchliffe16, E. Hines123, R.R. Hinman16,M. Hirose158, D. Hirschbuehl175,J. Hobbs149,N. Hod160a, M.C. Hodgkinson140, P. Hodgson140,A. Hoecker32, M.R. Hoeferkamp106,F. Hoenig101,M. Hohlfeld85,D. Hohn23, T.R. Holmes16,M. Homann45, T.M. Hong126, B.H. Hooberman166, W.H. Hopkins117, Y. Horii104, A.J. Horton143,J-Y. Hostachy57, S. Hou152,A. Hoummada136a,J. Howarth44, M. Hrabovsky116,
I. Hristova17,J. Hrivnac118,T. Hryn’ova5, A. Hrynevich95,C. Hsu146c,P.J. Hsu152,s, S.-C. Hsu139, D. Hu37, Q. Hu35b,Y. Huang44,Z. Hubacek129, F. Hubaut87, F. Huegging23,T.B. Huffman121,E.W. Hughes37, G. Hughes74,M. Huhtinen32,T.A. Hülsing85,P. Huo149,N. Huseynov67,b, J. Huston92, J. Huth59, G. Iacobucci51, G. Iakovidis27, I. Ibragimov142,L. Iconomidou-Fayard118,E. Ideal176,Z. Idrissi136e, P. Iengo32, O. Igonkina108, T. Iizawa171,Y. Ikegami68,M. Ikeno68,Y. Ilchenko11,t,D. Iliadis155, N. Ilic144, T. Ince102, G. Introzzi122a,122b,P. Ioannou9,∗,M. Iodice135a, K. Iordanidou37, V. Ippolito59, M. Ishino70, M. Ishitsuka158, R. Ishmukhametov112, C. Issever121,S. Istin20a,F. Ito161,J.M. Iturbe Ponce86,
R. Iuppa134a,134b,W. Iwanski41,H. Iwasaki68, J.M. Izen43,V. Izzo105a,S. Jabbar3,B. Jackson123, M. Jackson76,P. Jackson1, V. Jain2,K.B. Jakobi85,K. Jakobs50, S. Jakobsen32, T. Jakoubek128, D.O. Jamin115,D.K. Jana81, E. Jansen80,R. Jansky64, J. Janssen23,M. Janus56, G. Jarlskog83,
N. Javadov67,b, T. Jav ˚urek50, F. Jeanneau137, L. Jeanty16, J. Jejelava53a,u,G.-Y. Jeng151,D. Jennens90, P. Jenni50,v, J. Jentzsch45,C. Jeske170,S. Jézéquel5,H. Ji173,J. Jia149, H. Jiang66,Y. Jiang35b,S. Jiggins80,
