Measurement Of The Zz Production Cross Section And Z -> L(+)l(-)l '(+)l '(-) Branching Fraction In Pp Collisions At Root S=13tev

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https://www.sciencedirect.com/science/article/pii/S0370269316306256

DOI: 10.1016/j.physletb.2016.10.054

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©2016 by Elsevier. All rights reserved.

DIRETORIA DE TRATAMENTO DA INFORMAÇÃO Cidade Universitária Zeferino Vaz Barão Geraldo

CEP 13083-970 – Campinas SP Fone: (19) 3521-6493 http://www.repositorio.unicamp.br

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Measurement

of

the

ZZ

production

cross

section

and

Z

→ 

+



−



+



−

branching

fraction

in

pp

collisions

at

√

s

=

13 TeV

.TheCMS Collaboration

CERN,Switzerland

a r t i c l e i n f o a b s t ra c t

Articlehistory: Received29July2016

Receivedinrevisedform9October2016 Accepted21October2016

Availableonline27October2016 Editor: M.Doser

Keywords: CMS Physics Electroweak

Four-leptonproductioninproton–proton collisions,pp→ (Z/γ∗) (Z/γ∗)→ +−+−,where,=e orμ,isstudiedatacenter-of-massenergyof13 TeVwiththeCMSdetectorattheLHC.Thedatasample corresponds toan integrated luminosity of2.6 fb−1_{.The ZZ productioncross section, σ(pp→ZZ)=}

14.6+₋1₁._.9₈(stat)+₋0₀._.5₃(syst)±0.2(theo)±0.4(lumi)pb,ismeasuredforeventswithtwoopposite-sign, same-flavorleptonpairsproducedinthemassregion60<m+−,m+−<120 GeV.TheZbosonbranching

fraction to four leptons is measured to be _B(Z_{→ }+−+−)=4.9+₋0_0..8₇(stat)+₋0₀._.3₂(syst)+₋0₀._.2₁(theo)_± 0.1(lumi)×10−6_{forthefour-leptoninvariantmassintherange80<m}

+−+−<100 GeV anddilepton

massm+−>4 GeV forallopposite-sign,same-flavorleptonpairs.The resultsareinagreementwith

standardmodelpredictions.

©2016TheAuthor.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Measurements of diboson production at the CERN LHC allow precision studies of the standard model (SM). These measure-ments are important for testing predictions that were recently made available at next-to-next-to-leading-order (NNLO) in quan-tum chromodynamics (QCD) [1]. Comparing these predictions to data ata rangeof center-of-mass energies gives insightinto the structure of the electroweak gauge sector of the SM, and new proton–protoncollision dataat √s=13 TeV allow diboson mea-surements at the highest energies to date. Any deviations from expectedvaluescouldbeanindicationofphysicsbeyondtheSM.

PreviousmeasurementsoftheZZproductioncrosssectionfrom CMSwereperformedintheZZ→ +−+− andZZ→ +−νν

decaychannels,where=e, μand=e, μ, τ forbothZbosons producedon-shell,inthedileptonmass range60–120 GeV[2–4]. Thesemeasurements were madewithdata setscorresponding to integratedluminositiesof5.1 fb−1 at√s=7 TeV and19.6 fb−1 at

√

s=8 TeV,andagreewithSM predictions.TheATLAS Collabora-tionproducedsimilarresultsat√s=7,8,and13 TeV[5–7],which alsoagreewiththeSM.

Extending the mass window for the dilepton candidates to lower values allows measurements of (Z/γ∗) (Z/γ∗) production, where “Z” may indicate an on-shell Z boson or an off-shell

 _{E-mailaddress:cms-publication-committee-chair@cern.ch.}

Z∗ boson. The resulting sample includes Higgs boson events in the “golden channel” H→ZZ∗→ +−+−, where =e, μ, and rare Z boson decays to four leptons. The Z→ +−γ∗→

+−+− decaywas studied in detail at LEP [8] andwas ob-servedinppcollisionsbyCMS[9]andbyATLAS [10].Thoughthe branching fraction forthis decay is orders of magnitude smaller than that forthe Z→ +− decay,the precisely known mass of the Z boson makes the four-lepton mode useful for calibrating massmeasurementsofthenearbyHiggsresonance.

This letter reports a study of four-lepton production (pp→ +−+−,whereandindicateelectronsormuons)at√s=

13 TeV witha dataset correspondingtoan integratedluminosity of 2.62±0.07 fb−1 recorded in2015. Fromthisstudy,cross sec-tionsareinferredfornonresonantproductionofpairsofZ bosons, pp→ZZ, whereboth Z bosonsareproduced on-shell,definedas the massrange60–120 GeV,andresonantpp→Z→ +−+− production.Discussionof resonantHiggs bosonproductionis be-yondthescopeofthisletter.

2. TheCMSdetector

AdetaileddescriptionoftheCMSdetector,togetherwitha def-inition of thecoordinatesystemused andtherelevant kinematic variables,canbefoundinRef.[11].

The central feature of the CMS apparatus is a superconduct-ing solenoidof6 m internal diameter,providing amagneticfield of3.8 T.Withinthe solenoidvolumeare asiliconpixel andstrip http://dx.doi.org/10.1016/j.physletb.2016.10.054

0370-2693/©2016TheAuthor.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

tracker,aleadtungstatecrystalelectromagneticcalorimeter(ECAL), and a brass and scintillator hadron calorimeter (HCAL), which provide coverage in pseudorapidity |η|<1.479 in a barrel and 1.479<|η|<3.0 intwoendcapregions.Forwardcalorimeters ex-tendthecoverageprovidedbythebarrelandendcapdetectorsto

|η|<5.0.Muonsaremeasuredingas-ionizationdetectors embed-dedinthesteelflux-returnyokeoutsidethesolenoidintherange

|η|<2.4, with detection planes made using three technologies: drifttubes,cathodestripchambers,andresistiveplatechambers.

Electronmomentaareestimatedbycombiningenergy measure-mentsintheECALwithmomentummeasurements inthetracker. Themomentum resolution forelectrons withtransverse momen-tum pT≈45 GeV from Z→e+e− decays ranges from 1.7% for

nonshoweringelectronsinthebarrelregionto4.5%forshowering electronsintheendcaps[12].Matchingmuonstotracksmeasured in the silicon tracker results in a pT resolution for muons with

20<pT<100 GeV of1.3–2.0%inthebarrelandbetterthan 6%in

theendcaps.ThepT resolutioninthebarrelisbetterthan10%for

muonswithpTupto1 TeV[13].

3. Signalandbackgroundsimulation

Signaleventsare generatedwith powheg 2.0[14–16]at next-to-leading-order(NLO) inQCD forquark–antiquarkprocesses and leading-order (LO) for quark–gluon processes. This includes ZZ, Zγ∗,Z,and γ∗γ∗ productionwithaconstraintofm+−>4 GeV appliedbetweenallpairsofoppositelychargedleptonsatthe gen-eratorleveltoavoidinfrareddivergences.The gg→ZZ processis simulatedatLOwith mcfm v7.0[17].Thesesamplesarescaledto correspondto cross sectionscalculated atNNLO for qq→ZZ [1] (scalingK factor 1.1)andatNLO forgg→ZZ[18](K factor1.7). The gg→ZZ process is calculated to Oα5

s 

, where αs is the

strong coupling constant, while the other contributing processes arecalculated to Oα4

s 

; thishigher-order correction isincluded becausetheeffectisknowntobelarge[18].

AsampleofHiggsbosoneventsisproducedinthegluon–gluon fusion process with powheg 2.0 in the NLO QCD approximation. TheHiggsbosondecayismodeledwith jhugen 3.1.8[19–21].The qq→WZ processisgeneratedwith powheg 2.0.

The pythia v8.175 [22–24] package is used for parton show-ering, hadronization, and the underlying event simulation, with parameterssetbytheCUETP8M1tune[25].TheNNPDF3.0[26]set isused asthedefaultset ofpartondistribution functions(PDFs). For all simulated event samples, the PDFs are calculated to the sameorderinQCDastheprocessinthesample.

Thedetectorresponseissimulatedusingadetaileddescription oftheCMSdetectorimplemented withthe Geant4package [27]. The eventreconstruction is performedwiththe same algorithms used fordata. The simulated samples include additional interac-tions per bunch crossing, referred to as “pileup.” The simulated events are weighted so that the pileup distribution matches the data,withanaverageofabout11interactionsperbunchcrossing.

4. Eventreconstruction

All long-lived particles in each collision event — electrons, muons,photons,andchargedandneutralhadrons—areidentified andreconstructedwiththe CMSparticle-flow(PF) algorithm[28, 29]fromacombinationofthesignalsfromallsubdetectors. Recon-structedelectrons[12]andmuons[13]arecandidatesforinclusion infour-leptonfinalstatesiftheyhavepe_T>7 GeV and|ηe_{|<2.5 or}

pμ_T >5 GeV and|ημ|<2.4.Thesearedesignated“signalleptons.” Signal leptons are also required to originate from the event vertex,definedastheproton–protoninteractionvertexwhose as-sociatedchargedparticleshavethehighestsumofp2

T.Thedistance

ofclosestapproach betweeneach leptontrackandtheevent ver-tex isrequired tobe lessthan 0.5 cm inthe plane transverse to thebeamaxis,andlessthan1 cminthedirectionalongthebeam axis.Furthermore,thesignificanceofthethree-dimensionalimpact parameterrelativetotheeventvertex, SIP3D,isrequiredtosatisfy

SIP3D≡ |IP/σIP|<4 for each lepton, where IP is the distance of

closest approachofeach leptontracktothe eventvertexand σIP

isitsassociateduncertainty.

Signal leptons are requiredto beisolated fromother particles intheevent.Therelativeisolationisdefinedas

Riso=   charged hadrons pT +max  0,  neutral hadrons pT+  photons pT− pPUT  p_T, (1)

where the sums run over the charged and neutralhadrons, and photons,inaconedefinedbyR≡



(η)2+ (φ)2<0.3 around the lepton trajectory, where φ is the azimuthal angle inradians. Tominimize the contributionof chargedparticles frompileupto theisolationcalculation,chargedhadronsareincludedonlyifthey originatefromtheeventvertex.Thecontributionofneutral parti-cles frompileup is pPU

T .For electrons, pPUT is evaluated with the

“jetarea”methoddescribedinRef.[30];formuons,itistakento behalfthesumofthepTofallchargedparticlesinthecone

orig-inatingfrom pileupvertices.The factor one-halfaccountsfor the expected ratio of charged to neutral particle energy in hadronic interactions.AleptonisconsideredisolatedifRiso<0.35.

Emission of final-state radiation (FSR) photons by the signal leptons may degrade the performance of the isolation require-mentsandZ bosonmassreconstruction. Thesephotonsare omit-ted from the isolation determination for signal leptons and are implicitlyincludedindileptonkinematiccalculations.Photonsare FSR candidates if pγ_T >2 GeV, |ηγ_{|<2.4, their relative}

isola-tion (defined as in Eq. (1) with pPU

T =0) is less than 1.8, and

R(,γ) <0.5 withrespecttothenearestsignallepton.Toavoid double countingof bremmstrahlung photonsthat are already in-cludedinelectron reconstruction,photonsarenot FSRcandidates if there is anysignal electron within R(γ,e) <0.15 orwithin

|φ (γ,e)|<2 and|η(γ,e)|<0.05.BecauseFSRphotonshavea higheraverageenergythanphotonsfrompileupandareexpected tobemostlycollinearwiththeemittinglepton,aphotoncandidate isacceptedasFSRifR(,γ) /pγ_T2<0.012 GeV−2.

In simulatedZZ→ +−+− events, the efficiencyto select generatedFSRphotonsisaround55%,androughly85%ofselected photonsare matched to FSRphotons. At leastone FSR photonis identifiedinapproximately2%, 5%,and8% ofsimulatedeventsin the 4e, 2e2μ,and4μ channels, respectively. Indata eventswith twoon-shellZ bosons,noFSRphotonsareselectedinthe4e decay channel,whileatleastoneFSRphotonisselectedinthreeandfive eventsinthe2e2μand4μdecaychannels,respectively.

Theleptonreconstruction, identification,andisolation efficien-ciesaremeasuredwithatag-and-probetechnique[31] appliedto a sample of Z→ +− data events. The measurements are per-formed in several bins of p_T and |η_{|. The electron} reconstruc-tion and selection efficiency in the ECAL barrel (endcaps) varies from about 85% (77%) at pe_T≈10 GeV to about 95% (89%) for

pe_T≥20 GeV, whileinthebarrel-endcaptransitionregionthis ef-ficiencyisabout85%averagedoverallelectronswithpe_T>7 GeV. Themuonsarereconstructedandidentifiedwithefficienciesabove

5. Eventselection

The primary triggers for thisanalysis require the presence of apair oflooselyisolatedleptons ofthe sameordifferentflavors. ThehighestpTleptonmusthave pT>17 GeV,andthesubleading

leptonmusthavepe

T>12 GeV ifitisanelectronorp

μ

T >8 GeV if

itisamuon. Thedielectronanddimuontriggersrequirethatthe tracks corresponding to the leptons originate fromwithin 2 mm of each other in the plane transverse to the beam axis.Triggers requiringatriplet oflower-pT leptonswithno isolationcriterion,

orasingle high-pTelectronwithoutan isolationrequirement,are

also used.An event isused if it passesany trigger regardlessof the decay channel. The total trigger efficiency for events within theacceptanceofthisanalysisisgreaterthan98%.

AsignaleventmustcontainatleasttwoZ/γ∗ candidates,each formedfromanoppositelychargedpairofisolatedsignalelectrons or muons. Among the four leptons, the highest pT lepton must

have pT>20 GeV, andthe second-highest pT lepton must have

pe_T>12 GeV if itis an electron or pμ_T >10 GeV if it is amuon. AllleptonsarerequiredtobeseparatedbyR(1, 2) >0.02,and

electronsarerequiredtobeseparatedfrommuonsbyR(e,μ) > 0.05.

Within each event, all permutations of leptons givinga valid pair of Z/γ∗ candidates are considered separately. Within each +−+− candidate, the dilepton candidate with an invariant massclosest to 91.2 GeV,takenasthe nominalZ bosonmass,is denoted Z1 andis requiredto havea mass greater than40 GeV.

TheotherdileptoncandidateisdenotedZ2.BothmZ1 andmZ2 are requiredto belessthan 120 GeV.Allpairs ofoppositely charged leptonsinthecandidatearerequiredtohavem>4 GeV regard-lessofflavor.

Ifmultiple+−+− candidateswithinan eventpassall se-lections,thepassingcandidatewithmZ1 closesttothe nominalZ bosonmassischosen.Intherarecaseoffurtherambiguity,which mayariseineventswithfiveormoresignal leptons, theZ2

can-didate that maximizes the scalar pT sum of the four leptons is

chosen.

Additional requirements are applied toselect eventsfor mea-surements ofspecific processes.The →ZZ cross section is mea-sured using events where both mZ1 and mZ2 are greater than 60 GeV.TheZ→ +−+−branchingfractionismeasuredusing eventswith80<m_+_−_+_−<100 GeV, arangechosen toretain mostof the decaysin the resonancewhile removing most other processeswithfour-leptonfinalstates.

6. Backgroundestimate

ThemajorbackgroundcontributionsarisefromZ bosonandWZ dibosonproductioninassociationwithjetsandfromtt production. Inallthesecases,particlesfromjetfragmentationsatisfyboth lep-tonidentificationandisolationcriteria,andarethusmisidentified assignalleptons.

Theprobabilityforsuchobjectstobeselectedismeasuredfrom a sample of Z+ candidate events,where Z isa pair ofoppositely charged, same-flavor leptons that pass all analysis requirements and satisfy |m_+_−−mZ|<10 GeV, where mZ is the nominal Z

bosonmass.Eacheventinthissamplemusthaveexactlyone ad-ditionalobjectcandidatethat passesrelaxedidentification

require-ments withno isolation requirements applied. The misidentifica-tionprobability foreach leptonflavor isdefinedasaratioofthe numberofcandidates that passthe final isolation and identifica-tionrequirementstothetotalnumberinthesample,measuredin bins of lepton candidate pT and η. The number of Z+ candidate

eventsiscorrected forcontamination fromWZ production,orZZ productioninwhichoneleptonisnotreconstructed.Theseevents

Table 1

Thecontributionsofeachsourceofsignalsystematicuncertainty inthecrosssectionmeasurements.Theintegratedluminosity un-certaintyandthePDFandscaleuncertaintiesareconsidered sepa-rately.Allotheruncertaintiesareaddedinquadratureintoasingle systematicuncertainty.Uncertaintiesthatvarybydecaychannel arelistedasarange.

Uncertainty Z→4 ZZ→4 ID efficiency 2–6% 0.4–0.9% Isolation efficiency 1–6% 0.3–1.1% Trigger efficiency 2–4% 2% MC statistics 1–2% 1% Background 0.7–1.4% 0.7–2% Pileup 0.4–0.8% 0.2% PDF 1% 1% QCD scales 1% 1% Integrated luminosity 2.7% 2.7%

havea thirdgenuine,isolated leptonthat mustbeexcluded from the misidentification probability calculation. The WZ contamina-tionissuppressedbyrequiringthemissingtransverseenergyEmiss

T

tobebelow25 GeV.The Emiss_T isdefinedasthemagnitudeofthe missing transverse momentum vector pmiss_T , the projection onto the plane transverse tothe beams ofthe negative vector sumof themomentaofallreconstructedparticlesintheevent. Addition-ally, the transverse mass mT≡



(E_T+Emiss_T )2_{− (p}

T+ pmissT )2 of

candidateandthemissingtransversemomentumvectorisrequired

to be less than 30 GeV. The residualcontribution of WZ andZZ events, which may be up to a few percent of the events with candidatepassingallselectioncriteria,isestimatedfromsimulation

andsubtracted.

To account for all sources of background events, two control samplesareusedtoestimatethenumberofbackgroundeventsin thesignalregions.Botharedefinedtocontaineventswitha dilep-ton candidate satisfyingall requirements(Z1) andtwo additional

lepton candidates +−.In one control sample, enriched in WZ events, one  candidateis required to satisfy the full identifica-tion andisolation criteriaandtheother mustfailthe fullcriteria and instead satisfy only relaxed ones; in the other, enriched in Z+jets events,both candidatesmustsatisfytherelaxedcriteria, but fail the full criteria. The additional leptons must have oppo-site charge andthe same flavor (e±e∓, μ±μ∓). From this set of events, the expected numberof background events inthe signal region isobtainedby scalingthenumberofobserved Z1+ +−

events by the misidentification probability for each lepton fail-ingtheselection.Low-massdileptonsmaybesufficientlycollinear thattheirisolationconesoverlap,andtheirmisidentification prob-abilities are therefore correlated. To mitigate the effect of these correlations,onlythecontrolsampleinwhichbothadditional lep-tonsfailthefull selectionisusedifR+, −<0.6.The back-groundcontributionstothesignalregionsofZ→ +−+−and ZZ→ +−+−aresummarizedinSection8.

7. Systematicuncertainties

Systematic uncertainties are summarized in Table 1. In both data and simulated event samples,trigger efficiencies are evalu-atedwithatag-and-probe technique.The ratiobetweendataand simulation isappliedto simulatedevents,andthesize ofthe re-sultingchangeinexpectedyieldistakenastheuncertaintyforthe determination ofthetriggerefficiency.Thisuncertaintyis around 2%ofthefinalestimatedyield.ForZ→e+e−e+e−events,the un-certaintyincreasesto4%.

Theleptonidentificationandisolationefficienciesinsimulation are corrected with scaling factors derived with a tag-and-probe

methodandappliedasafunctionofleptonpTand η.Toestimate

theuncertaintiesassociatedwiththetag-and-probetechnique,the total yield is recomputed withthe scaling factors varied up and downbythetag-and-probe fituncertainties.Theuncertainties as-sociatedwiththeidentificationefficiencyintheZZ→ +−+− (Z→ +−+−)signal regions arefound tobe0.9% (6%)inthe 4e final state, 0.7% (4%) in the 2e2μ final state, and 0.4% (2%) inthe 4μ final state. The corresponding uncertainties associated withtheisolationefficiencyare1.1%(6%)inthe4e finalstate,0.7% (3%)in the 2e2μfinal state,and0.3% (1%) inthe 4μ final state. TheseuncertaintiesarehigherforZ→ +−+−eventsbecause theleptonsgenerallyhavelower pT,andthesamplesusedinthe

tag-and-probemethodhavefewereventsandmorecontamination fromnonpromptleptonsinthislow-pTregion.

Uncertaintiesduetotheeffectoffactorization(μF) and

renor-malization(μR)scalechoiceonthe Z Z→ +−+−acceptance

are evaluated with powheg and mcfm by varying the scales up anddown by a factor of two with respect to the defaultvalues

μF =μR=mZZ. These variations are much smaller than 1% and

areneglected.Parametricuncertainties(PDF+αs)areevaluated

us-ing the CT10 [32] and NNPDF3.0 sets and are found to be less than1%.Thelargestdifference betweenpredictionsfrom powheg and mcfm with differentscales andPDF sets,1.5%, is considered tobe thetheoreticaluncertaintyintheacceptancecalculation.An additionaltheoretical uncertaintyarisesfromscaling the powheg qq→ZZ simulatedsamplefromitsNLOcrosssectiontotheNNLO prediction, andthe mcfm gg→ZZ samples from their LO cross sections to the NLO predictions. The change in the acceptance corresponding to this scaling procedure is found to be 1.1%. All theoreticaluncertaintiesareaddedinquadrature.

Thelargestuncertaintyintheestimatedbackgroundyieldarises fromdifferencesinsample compositionbetweentheZ+ control sample used to calculate the lepton misidentification probability andtheZ+ +−controlsample.Afurtheruncertaintyarisesfrom the limitednumber of events in the Z+  sample. A systematic uncertaintyof40%oftheestimatedbackgroundyieldisappliedto coverbotheffects. Thesize ofthisuncertaintyvariesby channel, butislessthan1%ofthetotalexpectedyield.

Theuncertaintyintheintegratedluminosityofthedatasample is2.7%[33].

8. Crosssectionmeasurements

The distributions of the four-lepton mass and the masses of the Z1 and Z2 candidates are shown in Fig. 1. The SM

predic-tions include nonresonant ZZ predictions normalized using the NNLOcrosssection,productionoftheSM Higgsbosonwithmass 125 GeV[34],andresonantZ→ +−+−production.The back-groundestimatedfromdatais alsoshown. The reconstructed in-variant mass of the Z1 candidates, and a scatter plot showing

the correlation betweenmZ2 andmZ1 in data events,are shown inFig. 2. In the scatter plot,clusters of eventscorresponding to ZZ→ +−+−, Zγ∗→ +−+−, andZ→ +−+− pro-ductioncanbeseen.

The four-lepton invariant mass distribution below 110 GeV is shownin Fig. 3(top). Fig. 3(bottom) showsmZ2 plotted against

mZ1 foreventswithm+−+− between80 and100 GeV,andthe observedandexpectedeventyields inthismassregionare given inTable 2.

Thereconstructedfour-leptoninvariantmassisshowninFig. 4 (top)foreventswithtwoon-shellZ bosons.Fig. 4(bottom)shows theinvariantmassdistributionforallZ candidatesintheseevents. Thecorresponding observed andexpectedyields aregiven in Ta-ble 3.

Fig. 1. Distributionsof(top)thefour-leptoninvariant massm+−+− and (bot-tom)theinvariantmassofthedileptoncandidatesinallselectedfour-leptonevents, includingbothZ1 and Z2 ineachevent.Pointsrepresentthedata,whileshaded

histogramsrepresenttheSMpredictionandbackgroundestimate.Hatchedregions aroundthe predictedyieldrepresentcombinedstatistical,systematic,theoretical, andintegratedluminosityuncertainties.

The observed yields are used to evaluate the pp→Z→ +−+− andpp→ZZ→ +−+− productioncrosssections froma combinedfitto thenumberof observedeventsin allthe final states. The likelihood is a combination of individual chan-nellikelihoodsforthesignalandbackgroundhypotheseswiththe statisticalandsystematicuncertaintiesintheformofscaling nui-sanceparameters. The ratioofthe measured crosssection to the SM crosssection givenby thisfitincludingall channelsisscaled by thecrosssection usedin thesimulationto findthemeasured fiducialcrosssection.

The definitions for the fiducial phase spaces for the Z→ +−+−andZZ→ +−+−crosssectionmeasurementsare giveninTable 4.

Fig. 2. (top)ThedistributionofthereconstructedmassoftheZ1candidate.Points

representthedata,whileshadedhistogramsrepresenttheSMpredictionand back-groundestimate.Hatchedregionsaroundthepredictedyieldrepresentcombined statistical,systematic,theoretical,andintegratedluminosityuncertainties.(bottom) ThereconstructedmZ2 plottedagainstthereconstructedmZ1 indataevents,with distinctivemarkersforeachfinalstate.

Themeasuredcrosssectionsare

σfid(pp→Z→ +−+−)

=30.5+₋5₄._.2₇(stat)₋+1₁._.8₄(syst)±0.8 (lumi) fb,

σfid(pp→ZZ→ +−+−)

=34.8+₋4₄._.6₂(stat)₋+1₀._.2₈(syst)±0.9 (lumi) fb.

Thepp→Z→ +−+− fiducialcrosssectioncanbecompared to 27.9₋+1_1..0₅±0.6 fb calculated at NLO in QCD with powheg us-ingthesamesettingsasusedforthesimulatedsample described inSection3,withdynamicscales μF=μR=m+−+−.The un-certainties are for scale and PDF variations, respectively. The ZZ fiducial cross section can be compared to 34.4₋+₀0._.7₆±0.5 fb cal-culated with powheg and mcfm using the same settings as the simulatedsamples,withdynamicscales μF =μR=0.5m+−+− forthecontributionfrom mcfm.

Fig. 3. (top)Thedistributionofthereconstructedfour-leptonmassm+−+−for eventsselectedwithm+−+−<110 GeV.Pointsrepresentthedata,whileshaded histogramsrepresenttheSMpredictionandbackgroundestimate.Hatchedregions around thepredictedyieldrepresentcombinedstatistical,systematic,theoretical, and integrated luminosityuncertainties. (bottom)The reconstructedmZ2 plotted againstthereconstructedmZ1 indataeventsselectedwithm+−+−between80 and100 GeV,withdistinctivemarkersforeachfinalstate.

The pp→Z→ +−+− fiducial cross section is scaled to

σ(pp→Z)B(Z→4) usingthe acceptancecorrection factorA= 0.122±0.002, estimated with powheg. This factor corrects the fiducialZ→ +−+−crosssectiontothephasespacewithonly the 80–100 GeVmasswindowandm_+_−>4 GeV requirements, andalsoincludesacorrection,0.96±0.01,forthecontributionof nonresonantfour-leptonproductiontothesignalregion.The mea-suredcrosssectionis

σ(pp→Z)B(Z→ +−+−)

=250+₋43₃₉(stat)₋+15₁₁(syst)±4 (theo)±7 (lumi) fb. (2)

The branching fraction for the Z→ +−+− decay, B(Z→ +−+−),ismeasuredbycomparingthecrosssectiongivenby Eq.(2)withtheZ→ +−crosssection,andiscomputedas

Table 2

Theobservedandexpectedyieldsoffour-leptoneventsinthemassregion80<m+−+−<100 GeV andestimatedyieldsofbackgroundeventsevaluatedfromdata,shownforeachfinalstateandsummed inthetotalexpectedyield.Thefirstuncertaintyisstatistical,thesecondoneissystematic.

Final state Expected N+−+− Background Total expected Observed 4μ 16.88±0.14±0.62 0.31±0.30±0.12 17.19±0.33±0.63 17 2e2μ 15.88±0.14±0.87 0.37±0.27±0.15 16.25±0.31±0.88 16 4e 5.58±0.08±0.53 0.21±0.10±0.08 5.78±0.13±0.53 6 Total 38.33±0.21±1.19 0.89±0.42±0.22 39.22±0.47±1.21 39

Fig. 4. Distributionsof(top)thefour-leptoninvariantmassm+−+−and(bottom) dileptoncandidatemassforfour-leptoneventsselectedwithbothZ bosonson-shell. Pointsrepresentthedata,whileshadedhistogramsrepresenttheSMpredictionand backgroundestimate.Hatchedregionsaroundthepredictedyieldrepresent com-binedstatistical,systematic,theoretical,andintegratedluminosityuncertainties.

B(Z→ +−+−)

= σ(pp→Z→ +−+−)

C60–120

80–100σ(pp→Z→ +−)/B(Z→ +−)

,

where σ(pp→Z→ +−)=1870+₋50₄₀ pb is the Z→ +− cross section times branching fraction calculated at NNLO with

fewz_{v2.0[35] inthemassrange60–120 GeV.Itsuncertainty} in-cludes PDF uncertainties and uncertainties in αs, the charm and

bottom quark masses, and the effect of neglected higher-order correctionsto thecalculation. Thefactor C_80–10060–120=0.926±0.001 corrects for the difference in Z mass windows and is estimated using powheg. Its uncertainty includes scale and PDF variations. The nominal Z to dilepton branching fraction B(Z→ +−) is 0.03366[36].Themeasuredvalueis

B(Z→ +−+−)

=4.9₋+₀0._.8₇(stat)+₋0_0..₂3(syst)+₋0₀._.2₁(theo)±0.1 (lumi)×10−6,

wherethetheoreticaluncertaintyincludestheuncertainties inA, C60–120

80–100,and σ(pp→Z)B(Z→ +−).Thiscanbecomparedwith

4.6×10−6_{, computed with MadGraph5_aMC@NLO [37], and is}

consistentwiththeCMSandATLASmeasurementsat√s=7 and 8 TeV[9,10].

The total ZZ production cross section for both dileptons pro-ducedinthemassrange60–120 GeVandm+−>4 GeV isfound tobe

σ(pp→ZZ)

=14.6₋+₁1._.9₈(stat)+₋₀0_..5₃(syst)±0.2 (theo)±0.4 (lumi) pb.

The measured total cross section can be compared to the the-oretical value of 14.5₋+0₀._.5₄±0.2 pb calculated with a combina-tion of powheg and mcfm with the same settings as described for σfid(pp→ZZ→ +−+−). It can also be compared to

16.2+₋0_0..₄6 pb, calculated at NNLO in QCD via matrix [1,38], or 15.0+₋0₀._.7₆±0.2 pb, calculatedwith mcfm atNLO inQCD with ad-ditionalcontributionsfromLOgg→ZZ diagrams.Both valuesare calculatedwiththeNNPDF3.0PDFsets,atNNLOandNLO respec-tively,andfixedscalessetto μF=μR=mZ.

ThetotalZZ crosssectionisshowninFig. 5asafunctionofthe proton–protoncenter-of-massenergy.Results fromtheCMS[2–4] and ATLAS [5–7] experiments are compared to predictions from matrix and mcfm with the NNPDF3.0PDF sets andfixed scales

μF =μR =mZ. The matrix prediction uses PDFs calculated at

NNLO,whilethe mcfm predictionusesNLOPDFs.Theuncertainties are statistical(innerbars)andstatisticalandsystematicaddedin quadrature(outer bars).The band around the matrix predictions reflectsscaleuncertainties, whilethebandaround the mcfm pre-dictionsreflects both scaleandPDF uncertainties. Thetheoretical predictionsandallCMSmeasurementsareperformedinthe dilep-ton massrange 60–120 GeV.AllATLAS measurements are in the masswindow66–116 GeV.Thesmallermasswindowisestimated tocausea1.6%reductioninthemeasuredcrosssection.

9. Summary

Results have been presented for a study of four-lepton fi-nal states in proton–proton collisions at √s = 13 TeV with the CMS detector at the LHC. The pp→ZZ cross section has been measured to be σ(pp→ZZ)=14.6+₋1_1..9₈(stat)+₋0₀._.5₃(syst) ±

Table 3

TheobservedandexpectedyieldsofZZ events,andestimatedyieldsofbackgroundeventsevaluated fromdata,shownforeachfinalstateandsummedinthetotalexpectedyield.Thefirstuncertaintyis statistical,thesecondoneissystematic.

Final state Expected N+−+− Background Total expected Observed 4μ 21.80±0.15±0.46 0.00+₋00..2400+ 0.10 −0.00 21.80+ 0.28 −0.15+ 0.47 −0.46 26 2e2μ 36.15±0.20±0.81 0.60±0.34±0.24 36.75±0.34±0.85 30 4e 14.87±0.12±0.36 0.81±0.26±0.33 15.68±0.26±0.48 8 Total 72.82±0.27±1.00 1.42+0.49 −0.43+ 0.42 −0.41 74.23+ 0.56 −0.45+ 1.08 −1.08 64 Table 4

Fiducialdefinitionsforthereportedcrosssections.Thecommonrequirementsareappliedforboth mea-surements.

Cross section measurement Fiducial requirements Common requirements p1 T >20 GeV, p 2 T >10 GeV, p 3,4 T >5 GeV, |η_{| <2.5, m}

+−>4 GeV (any opposite-sign same-flavor pair) Z→ +_−_+_− _mZ

1>40 GeV

80<m+−+−<100 GeV ZZ→ +−+− 60<mZ1,mZ2<120 GeV

Fig. 5. ThetotalZZ crosssectionasafunctionoftheproton–protoncenter-of-mass energy.ResultsfromtheCMSandATLASexperimentsarecomparedtopredictions from matrix and mcfm withNNPDF3.0PDFsetsandfixedscalesμF=μR=mZ.

Detailsofthecalculationsanduncertaintiesaregiveninthetext.Measurementsat thesamecenter-of-massenergyareshiftedslightlyalongthex-axisforclarity.

0.2(theo)±0.4(lumi) pb forZ boson massesin the range 60<

mZ <120 GeV. The branching fraction for Z boson decays to

four leptons has been measured to be B(Z→ +−+−)= 4.9+₋0_0..₇8(stat)+₋0₀._.3₂(syst)+₋0₀._.2₁(theo) ± 0.1(lumi) × 10−6 _for

four-leptonmassintherange80<m+−+−<100 GeV anddilepton massm+−>4 GeV foralloppositelychargedsame-flavorlepton pairs.TheresultsareconsistentwithSMpredictions.

Acknowledgements

WethankMassimilianoGrazziniandhiscollaboratorsfor pro-viding the NNLO cross section calculations. We congratulate our colleagues in theCERN accelerator departments forthe excellent performance ofthe LHCand thankthetechnical and administra-tivestaffsatCERNandatotherCMSinstitutesfortheir contribu-tions to the successof the CMSeffort. In addition,we gratefully acknowledgethe computingcentersandpersonnel ofthe World-wideLHCComputingGridfordeliveringsoeffectivelythe

comput-ing infrastructure essential to our analyses. Finally, we acknowl-edge the enduring support forthe construction andoperation of the LHCandtheCMSdetectorprovidedby thefollowingfunding agencies: BMWFW andFWF(Austria); FNRSandFWO(Belgium); CNPq,CAPES, FAPERJ,andFAPESP(Brazil); MES (Bulgaria); CERN; CAS,MoST,andNSFC(China);COLCIENCIAS(Colombia);MSESand CSF(Croatia); RPF (Cyprus); SENESCYT(Ecuador);MoER, ERCIUT andERDF(Estonia); AcademyofFinland,MEC,andHIP (Finland); CEA andCNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM (Malaysia); BUAP, CIN-VESTAV, CONACYT,LNS,SEP, andUASLP-FAI(Mexico);MBIE(New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portu-gal);JINR(Dubna);MON,RosAtom,RASandRFBR(Russia);MESTD (Serbia);SEIDIandCPAN(Spain);SwissFundingAgencies (Switzer-land); MST (Taipei); ThEPCenter, IPST, STAR and NSTDA (Thai-land);TUBITAKandTAEK(Turkey);NASUandSFFR(Ukraine);STFC (UnitedKingdom);DOEandNSF(USA).

Individuals have received support from the Marie-Curie pro-gram and the European Research Council and EPLANET (Euro-pean Union); the Leventis Foundation; the A. P. Sloan Founda-tion; the Alexander von Humboldt Foundation; the Belgian Fed-eral Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technolo-gie (IWT-Belgium); the Ministry of Education, Youth and Sports (MEYS) of theCzech Republic; theCouncil of Scienceand Indus-trial Research, India; the HOMING PLUS program of the Foun-dation for Polish Science, cofinanced from European Union, Re-gional Development Fund, the Mobility Plus program of the Ministry of Science and Higher Education, the National Science Center (Poland), contracts Harmonia 2014/14/M/ST2/00428, Opus 2013/11/B/ST2/04202, 2014/13/B/ST2/02543 and 2014/15/B/ST2/ 03998, Sonata-bis 2012/07/E/ST2/01406; the Thalis and Aristeia programs cofinanced by EU-ESF and the Greek NSRF; the Na-tional Priorities Research Program by Qatar National Research Fund; the Programa Clarín-COFUND del Principado de Asturias; theRachadapisekSompotFundforPostdoctoralFellowship, Chula-longkornUniversityandtheChulalongkornAcademic intoIts2nd Century Project Advancement Project (Thailand); and the Welch Foundation,contractC-1845.

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CMSCollaboration

V. Khachatryan,A.M. Sirunyan, A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam, E. Asilar,T. Bergauer, J. Brandstetter, E. Brondolin, M. Dragicevic, J. Erö,M. Flechl, M. Friedl,

T. Matsushita, I. Mikulec,D. Rabady, N. Rad, B. Rahbaran, H. Rohringer, J. Schieck1, J. Strauss,

W. Treberer-Treberspurg,W. Waltenberger, C.-E. Wulz1

InstitutfürHochenergiephysikderOeAW,Wien,Austria

V. Mossolov,N. Shumeiko, J. Suarez Gonzalez

NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus

S. Alderweireldt, E.A. De Wolf,X. Janssen, J. Lauwers,M. Van De Klundert, H. Van Haevermaet,

P. Van Mechelen, N. Van Remortel,A. Van Spilbeeck

UniversiteitAntwerpen,Antwerpen,Belgium

S. Abu Zeid,F. Blekman, J. D’Hondt, N. Daci, I. De Bruyn, K. Deroover, N. Heracleous,S. Lowette,

S. Moortgat, L. Moreels,A. Olbrechts, Q. Python, S. Tavernier,W. Van Doninck, P. Van Mulders,

I. Van Parijs

VrijeUniversiteitBrussel,Brussel,Belgium

H. Brun, C. Caillol, B. Clerbaux, G. De Lentdecker, H. Delannoy, G. Fasanella, L. Favart, R. Goldouzian,

A. Grebenyuk,G. Karapostoli, T. Lenzi,A. Léonard,J. Luetic, T. Maerschalk, A. Marinov,A. Randle-conde,

T. Seva, C. Vander Velde, P. Vanlaer,R. Yonamine, F. Zenoni, F. Zhang2

UniversitéLibredeBruxelles,Bruxelles,Belgium

A. Cimmino,T. Cornelis, D. Dobur, A. Fagot, G. Garcia, M. Gul, D. Poyraz, S. Salva,R. Schöfbeck, M. Tytgat,

W. Van Driessche, E. Yazgan, N. Zaganidis

GhentUniversity,Ghent,Belgium

H. Bakhshiansohi,C. Beluffi3, O. Bondu,S. Brochet,G. Bruno, A. Caudron, S. De Visscher, C. Delaere,

M. Delcourt, L. Forthomme,B. Francois, A. Giammanco,A. Jafari, P. Jez,M. Komm, V. Lemaitre,

A. Magitteri,A. Mertens, M. Musich, C. Nuttens, K. Piotrzkowski,L. Quertenmont, M. Selvaggi,

M. Vidal Marono, S. Wertz

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

N. Beliy

UniversitédeMons,Mons,Belgium

W.L. Aldá Júnior, F.L. Alves,G.A. Alves, L. Brito,C. Hensel,A. Moraes, M.E. Pol, P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas, W. Carvalho,J. Chinellato4,A. Custódio, E.M. Da Costa, G.G. Da Silveira5,

D. De Jesus Damiao,C. De Oliveira Martins, S. Fonseca De Souza, L.M. Huertas Guativa, H. Malbouisson,

D. Matos Figueiredo, C. Mora Herrera,L. Mundim, H. Nogima,W.L. Prado Da Silva, A. Santoro,

A. Sznajder,E.J. Tonelli Manganote4, A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahujaa, C.A. Bernardesb, S. Dograa,T.R. Fernandez Perez Tomeia, E.M. Gregoresb, P.G. Mercadanteb,

C.S. Moona, S.F. Novaesa, Sandra S. Padulaa, D. Romero Abadb,J.C. Ruiz Vargas

a_{UniversidadeEstadualPaulista,SãoPaulo,Brazil} b_{UniversidadeFederaldoABC,SãoPaulo,Brazil}

A. Aleksandrov, R. Hadjiiska, P. Iaydjiev,M. Rodozov, S. Stoykova, G. Sultanov, M. Vutova

InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria

UniversityofSofia,Sofia,Bulgaria

W. Fang6

BeihangUniversity,Beijing,China

M. Ahmad, J.G. Bian, G.M. Chen,H.S. Chen, M. Chen, Y. Chen7,T. Cheng, C.H. Jiang, D. Leggat,Z. Liu,

F. Romeo,S.M. Shaheen, A. Spiezia,J. Tao, C. Wang, Z. Wang, H. Zhang, J. Zhao

InstituteofHighEnergyPhysics,Beijing,China

Y. Ban, G. Chen, Q. Li, S. Liu,Y. Mao, S.J. Qian,D. Wang, Z. Xu

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

C. Avila,A. Cabrera, L.F. Chaparro Sierra, C. Florez,J.P. Gomez, C.F. González Hernández, J.D. Ruiz Alvarez,

J.C. Sanabria

UniversidaddeLosAndes,Bogota,Colombia

N. Godinovic, D. Lelas,I. Puljak, P.M. Ribeiro Cipriano

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,D. Ferencek, K. Kadija,S. Micanovic, L. Sudic,T. Susa

InstituteRudjerBoskovic,Zagreb,Croatia

A. Attikis, G. Mavromanolakis,J. Mousa, C. Nicolaou, F. Ptochos,P.A. Razis, H. Rykaczewski

UniversityofCyprus,Nicosia,Cyprus

M. Finger8,M. Finger Jr.8

CharlesUniversity,Prague,Czechia

E. Carrera Jarrin

UniversidadSanFranciscodeQuito,Quito,Ecuador

A. Ellithi Kamel9,M.A. Mahmoud10,11, A. Radi11,12

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

B. Calpas,M. Kadastik, M. Murumaa, L. Perrini, M. Raidal, A. Tiko, C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,J. Pekkanen, M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Härkönen,V. Karimäki, R. Kinnunen, T. Lampén, K. Lassila-Perini,S. Lehti, T. Lindén,P. Luukka,

T. Peltola,J. Tuominiemi,E. Tuovinen, L. Wendland

HelsinkiInstituteofPhysics,Helsinki,Finland

J. Talvitie,T. Tuuva

M. Besancon, F. Couderc,M. Dejardin, D. Denegri, B. Fabbro,J.L. Faure, C. Favaro,F. Ferri, S. Ganjour,

S. Ghosh, A. Givernaud, P. Gras, G. Hamel de Monchenault,P. Jarry, I. Kucher, E. Locci,M. Machet,

J. Malcles,J. Rander, A. Rosowsky, M. Titov, A. Zghiche

IRFU,CEA,UniversitéParis-Saclay,Gif-sur-Yvette,France

A. Abdulsalam, I. Antropov, S. Baffioni, F. Beaudette, P. Busson, L. Cadamuro, E. Chapon, C. Charlot,

O. Davignon,R. Granier de Cassagnac, M. Jo, S. Lisniak,P. Miné, M. Nguyen, C. Ochando, G. Ortona,

P. Paganini, P. Pigard,S. Regnard, R. Salerno, Y. Sirois,T. Strebler, Y. Yilmaz, A. Zabi

LaboratoireLeprince-Ringuet,EcolePolytechnique,IN2P3-CNRS,Palaiseau,France

J.-L. Agram13, J. Andrea, A. Aubin, D. Bloch,J.-M. Brom, M. Buttignol,E.C. Chabert, N. Chanon, C. Collard,

E. Conte13, X. Coubez, J.-C. Fontaine13,D. Gelé, U. Goerlach,A.-C. Le Bihan, J.A. Merlin14,K. Skovpen,

P. Van Hove

InstitutPluridisciplinaireHubertCurien,UniversitédeStrasbourg,UniversitédeHauteAlsaceMulhouse,CNRS/IN2P3,Strasbourg,France

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,C. Bernet, G. Boudoul, E. Bouvier, C.A. Carrillo Montoya, R. Chierici,D. Contardo,

B. Courbon, P. Depasse, H. El Mamouni, J. Fan, J. Fay, S. Gascon, M. Gouzevitch, G. Grenier, B. Ille,

F. Lagarde, I.B. Laktineh,M. Lethuillier, L. Mirabito,A.L. Pequegnot, S. Perries, A. Popov15, D. Sabes,

V. Sordini,M. Vander Donckt, P. Verdier,S. Viret

UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS-IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France

T. Toriashvili16

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze8

TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann, S. Beranek,L. Feld, A. Heister, M.K. Kiesel, K. Klein, M. Lipinski, A. Ostapchuk, M. Preuten,

F. Raupach, S. Schael, C. Schomakers,J.F. Schulte, J. Schulz,T. Verlage, H. Weber, V. Zhukov15

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

M. Brodski,E. Dietz-Laursonn, D. Duchardt, M. Endres, M. Erdmann,S. Erdweg, T. Esch, R. Fischer,

A. Güth, M. Hamer,T. Hebbeker,C. Heidemann, K. Hoepfner,S. Knutzen, M. Merschmeyer,A. Meyer,

P. Millet,S. Mukherjee, M. Olschewski, K. Padeken,T. Pook,M. Radziej, H. Reithler, M. Rieger,F. Scheuch,

L. Sonnenschein, D. Teyssier,S. Thüer

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

V. Cherepanov, G. Flügge, W. Haj Ahmad, F. Hoehle, B. Kargoll, T. Kress, A. Künsken,J. Lingemann,

A. Nehrkorn, A. Nowack,I.M. Nugent, C. Pistone, O. Pooth,A. Stahl14

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin,C. Asawatangtrakuldee, K. Beernaert, O. Behnke,U. Behrens, A.A. Bin Anuar,

K. Borras17,A. Campbell, P. Connor, C. Contreras-Campana, F. Costanza, C. Diez Pardos,G. Dolinska,

G. Eckerlin, D. Eckstein, E. Eren, E. Gallo18, J. Garay Garcia, A. Geiser, A. Gizhko, J.M. Grados Luyando,

P. Gunnellini, A. Harb, J. Hauk, M. Hempel19,H. Jung,A. Kalogeropoulos,O. Karacheban19,M. Kasemann,

J. Keaveney, J. Kieseler, C. Kleinwort,I. Korol, D. Krücker, W. Lange,A. Lelek, J. Leonard, K. Lipka,

A. Lobanov, W. Lohmann19,R. Mankel, I.-A. Melzer-Pellmann, A.B. Meyer, G. Mittag, J. Mnich,

T. Schoerner-Sadenius,C. Seitz,S. Spannagel, N. Stefaniuk,K.D. Trippkewitz, G.P. Van Onsem, R. Walsh, C. Wissing

DeutschesElektronen-Synchrotron,Hamburg,Germany

V. Blobel, M. Centis Vignali, A.R. Draeger,T. Dreyer, E. Garutti, K. Goebel, D. Gonzalez, J. Haller,

M. Hoffmann,A. Junkes, R. Klanner,R. Kogler,N. Kovalchuk,T. Lapsien, T. Lenz,I. Marchesini,D. Marconi,

M. Meyer,M. Niedziela, D. Nowatschin, J. Ott, F. Pantaleo14,T. Peiffer, A. Perieanu, J. Poehlsen, C. Sander,

C. Scharf,P. Schleper, A. Schmidt,S. Schumann, J. Schwandt,H. Stadie,G. Steinbrück, F.M. Stober,

M. Stöver,H. Tholen, D. Troendle, E. Usai, L. Vanelderen,A. Vanhoefer, B. Vormwald

UniversityofHamburg,Hamburg,Germany

C. Barth,C. Baus, J. Berger,E. Butz, T. Chwalek, F. Colombo, W. De Boer,A. Dierlamm, S. Fink,R. Friese,

M. Giffels,A. Gilbert,P. Goldenzweig, D. Haitz, F. Hartmann14,S.M. Heindl, U. Husemann,I. Katkov15,

P. Lobelle Pardo, B. Maier, H. Mildner, M.U. Mozer,T. Müller, Th. Müller, M. Plagge, G. Quast,

K. Rabbertz,S. Röcker, F. Roscher,M. Schröder, I. Shvetsov, G. Sieber,H.J. Simonis, R. Ulrich,

J. Wagner-Kuhr,S. Wayand, M. Weber, T. Weiler, S. Williamson,C. Wöhrmann, R. Wolf

InstitutfürExperimentelleKernphysik,Karlsruhe,Germany

G. Anagnostou,G. Daskalakis, T. Geralis,V.A. Giakoumopoulou, A. Kyriakis, D. Loukas,I. Topsis-Giotis

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

A. Agapitos,S. Kesisoglou, A. Panagiotou,N. Saoulidou, E. Tziaferi

NationalandKapodistrianUniversityofAthens,Athens,Greece

I. Evangelou,G. Flouris, C. Foudas, P. Kokkas, N. Loukas, N. Manthos,I. Papadopoulos, E. Paradas

UniversityofIoánnina,Ioánnina,Greece

N. Filipovic

MTA-ELTELendületCMSParticleandNuclearPhysicsGroup,EötvösLorándUniversity,Budapest,Hungary

G. Bencze,C. Hajdu, P. Hidas,D. Horvath20, F. Sikler,V. Veszpremi, G. Vesztergombi21, A.J. Zsigmond

WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni,S. Czellar, J. Karancsi22,A. Makovec,J. Molnar, Z. Szillasi

InstituteofNuclearResearchATOMKI,Debrecen,Hungary

M. Bartók21,P. Raics, Z.L. Trocsanyi, B. Ujvari

UniversityofDebrecen,Debrecen,Hungary

S. Bahinipati, S. Choudhury23,P. Mal, K. Mandal, A. Nayak24,D.K. Sahoo, N. Sahoo,S.K. Swain

NationalInstituteofScienceEducationandResearch,Bhubaneswar,India

S. Bansal,S.B. Beri, V. Bhatnagar, R. Chawla, U. Bhawandeep, A.K. Kalsi,A. Kaur, M. Kaur, R. Kumar,

A. Mehta,M. Mittal, J.B. Singh, G. Walia

PanjabUniversity,Chandigarh,India

Ashok Kumar,A. Bhardwaj, B.C. Choudhary, R.B. Garg,S. Keshri, S. Malhotra,M. Naimuddin, N. Nishu,

K. Ranjan,R. Sharma, V. Sharma

R. Bhattacharya,S. Bhattacharya, K. Chatterjee, S. Dey,S. Dutt, S. Dutta, S. Ghosh, N. Majumdar,

A. Modak, K. Mondal, S. Mukhopadhyay, S. Nandan, A. Purohit,A. Roy, D. Roy, S. Roy Chowdhury,

S. Sarkar,M. Sharan, S. Thakur

SahaInstituteofNuclearPhysics,Kolkata,India

P.K. Behera

IndianInstituteofTechnologyMadras,Madras,India

R. Chudasama, D. Dutta, V. Jha,V. Kumar, A.K. Mohanty14,P.K. Netrakanti,L.M. Pant, P. Shukla,A. Topkar

BhabhaAtomicResearchCentre,Mumbai,India

T. Aziz, S. Dugad,G. Kole, B. Mahakud, S. Mitra, G.B. Mohanty, B. Parida, N. Sur, B. Sutar

TataInstituteofFundamentalResearch-A,Mumbai,India

S. Banerjee, S. Bhowmik25,R.K. Dewanjee, S. Ganguly, M. Guchait,Sa. Jain, S. Kumar, M. Maity25,

G. Majumder, K. Mazumdar,T. Sarkar25, N. Wickramage26

TataInstituteofFundamentalResearch-B,Mumbai,India

S. Chauhan,S. Dube, V. Hegde, A. Kapoor, K. Kothekar, A. Rane, S. Sharma

IndianInstituteofScienceEducationandResearch(IISER),Pune,India

H. Behnamian,S. Chenarani27,E. Eskandari Tadavani,S.M. Etesami27, A. Fahim28, M. Khakzad,

M. Mohammadi Najafabadi, M. Naseri, S. Paktinat Mehdiabadi, F. Rezaei Hosseinabadi, B. Safarzadeh29,

M. Zeinali

InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran

M. Felcini,M. Grunewald

UniversityCollegeDublin,Dublin,Ireland

M. Abbresciaa,b, C. Calabriaa,b,C. Caputoa,b,A. Colaleoa,D. Creanzaa,c, L. Cristellaa,b,N. De Filippisa,c,

M. De Palmaa,b, L. Fiorea,G. Iasellia,c, G. Maggia,c,M. Maggia, G. Minielloa,b, S. Mya,b, S. Nuzzoa,b,

A. Pompilia,b,G. Pugliesea,c,R. Radognaa,b,A. Ranieria,G. Selvaggia,b,L. Silvestrisa,14, R. Vendittia,b,

P. Verwilligena

a_{INFNSezionediBari,Bari,Italy} b_{UniversitàdiBari,Bari,Italy} c_{PolitecnicodiBari,Bari,Italy}

G. Abbiendia,C. Battilana, D. Bonacorsia,b, S. Braibant-Giacomellia,b, L. Brigliadoria,b, R. Campaninia,b,

P. Capiluppia,b,A. Castroa,b,F.R. Cavalloa,S.S. Chhibraa,b, G. Codispotia,b, M. Cuffiania,b,

G.M. Dallavallea,F. Fabbria, A. Fanfania,b, D. Fasanellaa,b,P. Giacomellia,C. Grandia,L. Guiduccia,b,

S. Marcellinia, G. Masettia, A. Montanaria, F.L. Navarriaa,b,A. Perrottaa, A.M. Rossia,b,T. Rovellia,b,

G.P. Sirolia,b,N. Tosia,b,14

a_{INFNSezionediBologna,Bologna,Italy} b_{UniversitàdiBologna,Bologna,Italy}

S. Albergoa,b,M. Chiorbolia,b,S. Costaa,b,A. Di Mattiaa,F. Giordanoa,b,R. Potenzaa,b,A. Tricomia,b,

C. Tuvea,b

a_{INFNSezionediCatania,Catania,Italy} b_{UniversitàdiCatania,Catania,Italy}

G. Barbaglia, V. Ciullia,b,C. Civininia, R. D’Alessandroa,b,E. Focardia,b,V. Goria,b, P. Lenzia,b,

M. Meschinia, S. Paolettia,G. Sguazzonia,L. Viliania,b,14

b_{UniversitàdiFirenze,Firenze,Italy}

L. Benussi,S. Bianco, F. Fabbri, D. Piccolo,F. Primavera14

INFNLaboratoriNazionalidiFrascati,Frascati,Italy

V. Calvellia,b, F. Ferroa, M. Lo Veterea,b, M.R. Mongea,b,E. Robuttia, S. Tosia,b

a_{INFNSezionediGenova,Genova,Italy} b_{UniversitàdiGenova,Genova,Italy}

L. Brianza14, M.E. Dinardoa,b,S. Fiorendia,b, S. Gennaia, A. Ghezzia,b,P. Govonia,b, S. Malvezzia,

R.A. Manzonia,b,14,B. Marzocchia,b,D. Menascea,L. Moronia,M. Paganonia,b, D. Pedrinia,S. Pigazzini,

S. Ragazzia,b,T. Tabarelli de Fatisa,b

a_{INFNSezionediMilano-Bicocca,Milano,Italy} b_{UniversitàdiMilano-Bicocca,Milano,Italy}

S. Buontempoa, N. Cavalloa,c,G. De Nardo, S. Di Guidaa,d,14,M. Espositoa,b,F. Fabozzia,c,

A.O.M. Iorioa,b,G. Lanzaa,L. Listaa, S. Meolaa,d,14, P. Paoluccia,14, C. Sciaccaa,b, F. Thyssen

a_{INFNSezionediNapoli,Napoli,Italy} b_{UniversitàdiNapoli‘FedericoII’,Napoli,Italy} c_{UniversitàdellaBasilicata,Potenza,Italy} d_{UniversitàG.Marconi,Roma,Italy}

P. Azzia,14,N. Bacchettaa,L. Benatoa,b, D. Biselloa,b, A. Bolettia,b, R. Carlina,b,

A. Carvalho Antunes De Oliveiraa,b,P. Checchiaa, M. Dall’Ossoa,b,P. De Castro Manzanoa, T. Dorigoa,

U. Dossellia,F. Gasparinia,b,U. Gasparinia,b, A. Gozzelinoa, S. Lacapraraa,M. Margonia,b,

A.T. Meneguzzoa,b,J. Pazzinia,b,14, N. Pozzobona,b, P. Ronchesea,b,F. Simonettoa,b, E. Torassaa,

M. Zanetti,P. Zottoa,b, A. Zucchettaa,b,G. Zumerlea,b

a_{INFNSezionediPadova,Padova,Italy} b_{UniversitàdiPadova,Padova,Italy} c_{UniversitàdiTrento,Trento,Italy}

A. Braghieria, A. Magnania,b, P. Montagnaa,b,S.P. Rattia,b,V. Rea, C. Riccardia,b, P. Salvinia, I. Vaia,b,

P. Vituloa,b

a_{INFNSezionediPavia,Pavia,Italy} b_{UniversitàdiPavia,Pavia,Italy}

L. Alunni Solestizia,b, G.M. Bileia,D. Ciangottinia,b,L. Fanòa,b, P. Laricciaa,b, R. Leonardia,b,

G. Mantovania,b, M. Menichellia,A. Sahaa,A. Santocchiaa,b

a_{INFNSezionediPerugia,Perugia,Italy} b_{UniversitàdiPerugia,Perugia,Italy}

K. Androsova,30,P. Azzurria,14,G. Bagliesia,J. Bernardinia,T. Boccalia,R. Castaldia, M.A. Cioccia,30,

R. Dell’Orsoa,S. Donatoa,c,G. Fedi, A. Giassia,M.T. Grippoa,30,F. Ligabuea,c, T. Lomtadzea, L. Martinia,b,

A. Messineoa,b, F. Pallaa,A. Rizzia,b,A. Savoy-Navarroa,31, P. Spagnoloa,R. Tenchinia, G. Tonellia,b,

A. Venturia,P.G. Verdinia

a_{INFNSezionediPisa,Pisa,Italy} b_{UniversitàdiPisa,Pisa,Italy}

c_{ScuolaNormaleSuperiorediPisa,Pisa,Italy}

L. Baronea,b, F. Cavallaria,M. Cipriania,b, G. D’imperioa,b,14,D. Del Rea,b,14,M. Diemoza, S. Gellia,b,

C. Jordaa, E. Longoa,b, F. Margarolia,b,P. Meridiania,G. Organtinia,b, R. Paramattia,F. Preiatoa,b,

S. Rahatloua,b,C. Rovellia, F. Santanastasioa,b

a_{INFNSezionediRoma,Roma,Italy} b_{UniversitàdiRoma,Roma,Italy}

N. Amapanea,b, R. Arcidiaconoa,c,14, S. Argiroa,b, M. Arneodoa,c, N. Bartosika, R. Bellana,b,C. Biinoa,

N. Cartigliaa, F. Cennaa,b,M. Costaa,b, R. Covarellia,b,A. Deganoa,b,N. Demariaa, L. Fincoa,b, B. Kiania,b,

C. Mariottia, S. Masellia, E. Migliorea,b,V. Monacoa,b,E. Monteila,b,M.M. Obertinoa,b,L. Pachera,b,

N. Pastronea,M. Pelliccionia, G.L. Pinna Angionia,b,F. Raveraa,b,A. Romeroa,b,M. Ruspaa,c, R. Sacchia,b,

K. Shchelinaa,b, V. Solaa, A. Solanoa,b,A. Staianoa, P. Traczyka,b

a_{INFNSezionediTorino,Torino,Italy} b_{UniversitàdiTorino,Torino,Italy}

c_{UniversitàdelPiemonteOrientale,Novara,Italy}

S. Belfortea,M. Casarsaa, F. Cossuttia, G. Della Riccaa,b,C. La Licataa,b,A. Schizzia,b, A. Zanettia

a_{INFNSezionediTrieste,Trieste,Italy} b_{UniversitàdiTrieste,Trieste,Italy}

D.H. Kim,G.N. Kim, M.S. Kim,S. Lee, S.W. Lee, Y.D. Oh, S. Sekmen,D.C. Son,Y.C. Yang

KyungpookNationalUniversity,Daegu,RepublicofKorea

A. Lee

ChonbukNationalUniversity,Jeonju,RepublicofKorea

J.A. Brochero Cifuentes, T.J. Kim

HanyangUniversity,Seoul,RepublicofKorea

S. Cho,S. Choi, Y. Go, D. Gyun,S. Ha, B. Hong,Y. Jo, Y. Kim, B. Lee, K. Lee, K.S. Lee, S. Lee,J. Lim,

S.K. Park,Y. Roh

KoreaUniversity,Seoul,RepublicofKorea

J. Almond, J. Kim,S.B. Oh, S.h. Seo,U.K. Yang, H.D. Yoo,G.B. Yu

SeoulNationalUniversity,Seoul,RepublicofKorea

M. Choi,H. Kim, H. Kim,J.H. Kim, J.S.H. Lee, I.C. Park, G. Ryu, M.S. Ryu

UniversityofSeoul,Seoul,RepublicofKorea

Y. Choi,J. Goh, C. Hwang, J. Lee,I. Yu

SungkyunkwanUniversity,Suwon,RepublicofKorea

V. Dudenas, A. Juodagalvis,J. Vaitkus

VilniusUniversity,Vilnius,Lithuania

I. Ahmed,Z.A. Ibrahim, J.R. Komaragiri, M.A.B. Md Ali32,F. Mohamad Idris33,W.A.T. Wan Abdullah,

M.N. Yusli,Z. Zolkapli

NationalCentreforParticlePhysics,UniversitiMalaya,KualaLumpur,Malaysia

H. Castilla-Valdez, E. De La Cruz-Burelo,I. Heredia-De La Cruz34,A. Hernandez-Almada,

R. Lopez-Fernandez, R. Magaña Villalba, J. Mejia Guisao,A. Sanchez-Hernandez

CentrodeInvestigacionydeEstudiosAvanzadosdelIPN,MexicoCity,Mexico

S. Carrillo Moreno, C. Oropeza Barrera, F. Vazquez Valencia

UniversidadIberoamericana,MexicoCity,Mexico

S. Carpinteyro, I. Pedraza, H.A. Salazar Ibarguen, C. Uribe Estrada