Measurement of the pp→ZZ production cross section and constraints on anomalous triple gauge couplings in four-lepton final states at s=8 TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Measurement

of

the

pp

_→

ZZ production

cross

section

and

constraints

on

anomalous

triple

gauge

couplings

in

four-lepton

final

states

at

√

_s

=

8 TeV

Receivedinrevisedform20November2014 Accepted30November2014

Availableonline4December2014 Editor:M.Doser

Keywords:

CMS Physics Electroweak

AmeasurementoftheinclusiveZZ productioncrosssectionandconstraintsonanomaloustriplegauge couplings in proton–proton collisions at √s₌8 TeV are presented. The analysis is based on adata sample, correspondingtoanintegratedluminosityof19.6 fb−1_{,collectedwiththeCMSexperiment at} the LHC. The measurements are performedinthe leptonicdecaymodes ZZ_{→ ℓℓℓ}′_ℓ′_{,where ℓ=e,µ}

andℓ′₌e,µ,τ.Themeasuredtotalcrosssectionσ(pp_→ZZ)₌7.7_±0.5 (stat)+0.5

−0.4(syst)±0.4(theo)± 0.2 (lumi) pb, for bothZ bosons produced inthe mass range 60<mZ<120 GeV,is consistentwith standardmodelpredictions.Differentialcrosssectionsaremeasuredandwelldescribedbythetheoretical predictions.Theinvariantmassdistributionofthefour-leptonsystemisusedtosetlimitsonanomalous ZZZ and ZZγ couplings at the 95% confidence level: ₋0.004< f₄Z<0.004, −0.004< f₅Z<0.004, −0.005<f₄γ<0.005,and−0.005<f₅γ<0.005.

©2014TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/3.0/).FundedbySCOAP3_.

1. Introduction

The study of diboson production in proton–proton collisions provides animportant testofthe electroweaksector ofthe stan-dard model(SM), especially thenon-Abelian structure ofthe SM Lagrangian. In the SM, ZZ production proceeds mainly through quark–antiquark t- and u-channel scattering diagrams. At high-ordercalculationsinQCD,gluon–gluon fusionalsocontributesvia boxdiagramswith quark loops.There are notree-level contribu-tionstoZZ productionfromtriplegaugebosonverticesintheSM. Anomalous triple gauge couplings (ATGC) ZZZ and ZZγ are in-troducedusing an effective Lagrangian following Ref. [1]. In this parametrization, two ZZZ andtwo ZZγ couplings are allowed by electromagnetic gauge invariance and Lorentz invariance for on-shellZ bosonsandareparametrizedbytwoCP-violating( fV

4)and

two CP-conserving ( f₅V) parameters, where V= (Z, γ). Nonzero ATGCvaluescouldbeinducedbynewphysics modelssuch as su-persymmetry[2].

PreviousmeasurementsoftheinclusiveZZcrosssectionbythe CMSCollaborationattheLHCwereperformedintheZZ→ ℓℓℓ′_ℓ′

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

decay channels, where ℓ=e, µ and ℓ′=e, µ, τ, with the data corresponding to an integrated luminosity of 5.1 (5.0)fb−1 at √_s

=7(8)TeV[3,4].Themeasuredtotalcrosssection, σ(pp→ZZ), is 6.24₋+₀0._.86₈₀(stat)+₋₀0_..41₃₂(syst)±0.14 (lumi) pb at √s=7 TeV and 8.4±1.0 (stat) ±0.7 (syst)±0.4 (lumi) pb at √s=8 TeV for both Z bosons in the mass range 60 <mZ <120 GeV. The ATLAS Collaboration measured a total cross section of 6.7± 0.7 (stat)+0.4

−0.3 (syst)±0.3 (lumi) pb[5]usingZZ→ ℓℓℓℓandZZ→

ℓℓνν final states with a data sample corresponding to an in-tegrated luminosity of 4.6 fb−1 at √s=7 TeV and 66<mZ < 116 GeV. Measurements of the ZZ cross sections performed at the Tevatronare summarizedinRefs. [6,7].Allmeasurements are foundtoagreewiththecorrespondingSMpredictions.

Limits on ZZZ and ZZγ ATGCs were set by CMS using the 7 TeV data sample: −0.011< f₄Z<0.012, −0.012< f₅Z<0.012, −0.013< f₄γ <0.015, and −0.014< f₅γ <0.014 at 95% confi-dencelevel(CL)[3].SimilarlimitswereobtainedbyATLAS[5].

In thisanalysis, which isbased onthe full 2012data setand corresponds to an integratedluminosity of19.6 fb−1, results are presented for the ZZ inclusive and differential cross sections as well aslimitsfortheZZZ and ZZγ ATGCs.Thecross sectionsare measuredforbothZ bosonsinthemassrange60<mZ<120 GeV; contributionsfromvirtualphotonexchangeareincluded.

http://dx.doi.org/10.1016/j.physletb.2014.11.059

0370-2693/©2014TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/3.0/).Fundedby SCOAP3_.

2. The CMS detector and simulation

TheCMSdetectorisdescribed indetailelsewhere[8];thekey componentsfor thisanalysis are summarized here. The CMS ex-perimentuses a right-handed coordinatesystem, with theorigin atthe nominalinteraction point, the x axis pointingto the cen-teroftheLHC ring,the y axis pointingup(perpendicular tothe planeoftheLHCring),andthez axisalongthe counterclockwise-beamdirection.Thepolarangleθ ismeasuredfromthepositive z axisandtheazimuthalangleφismeasuredinthex–y plane.The magnitudeof thetransversemomentum is pT=

!

p2

x+p2y. A

su-perconductingsolenoidislocatedinthecentralregionoftheCMS detector,providing an axialmagnetic field of3.8T parallel to the beamdirection. Asiliconpixelandstrip tracker,acrystal electro-magnetic calorimeter(ECAL), anda brass andscintillator hadron calorimeterarelocatedwithinthesolenoidandcovertheabsolute pseudorapidityrange|η|<3.0,wherepseudorapidityisdefinedas

η= −ln[tan(θ/2)].TheECALbarrelregion(EB)covers|η|<1.479 andtwo endcap regions (EE) cover 1.479<_|η|<3.0. A quartz-fiberCherenkovcalorimeterextendsthecoverage upto |η|<5.0. Gas ionization muon detectors are embedded in the steel flux-returnyokeoutside thesolenoid. A firstlevel ofthe CMStrigger system, composedof custom hardware processors,is designedto selecteventsofinterestinlessthan 4 µsusinginformation from thecalorimetersandmuondetectors.A high-level-trigger proces-sorfarmreducestheeventratefrom100 kHzdeliveredbythefirst leveltriggertoafewhundredhertz.

SeveralMonte Carlo(MC) eventgenerators are used to simu-late the signal and background contributions. The qq→ZZ pro-cessisgeneratedatnext-to-leadingorder(NLO)with powheg 2.0 [9–11]oratleading-order(LO)with sherpa[12].Thegg→ZZ pro-cessissimulatedwith gg2zz[13] atLO. Otherdibosonprocesses (WZ,Zγ)andtheZ+jets samplesaregeneratedatLOwith Mad-Graph 5[14].Eventsfromtt productionaregeneratedatNLOwith powheg.The pythia 6.4[15]packageisusedforpartonshowering, hadronization,andtheunderlyingeventsimulation.Thedefaultset of parton distribution functions (PDF) used for LO generators is CTEQ6L[16],whereas CT10 [17] is used forNLO generators. The ZZ yieldsfromsimulation are scaled accordingto the theoretical crosssectionscalculatedwith mcfm 6.0[18] atNLO forqq→ZZ andatLOforgg→ZZ with theMSTW2008PDF [19]with renor-malizationandfactorizationscalessetto µR=µF=91.2 GeV.The

τ-leptondecaysaresimulatedwith tauola[20].Forallprocesses, thedetectorresponseissimulatedusingadetaileddescriptionof theCMSdetectorbasedonthe Geant4package[21],andevent re-constructionisperformedwiththesamealgorithmsthatareused fordata.Thesimulatedsamplesinclude multipleinteractions per bunchcrossing(pileup),suchthatthepileupdistributionmatches that of data,with an average value of about21 interactions per bunchcrossing.

3. Event reconstruction

A complete reconstruction of the individual particles emerg-ing fromeach collision eventis obtained via a particle-flow(PF) technique [22,23],whichuses theinformation fromall CMS sub-detectors to identify and reconstruct individual particles in the collisionevent.Theparticles areclassifiedintomutuallyexclusive categories:chargedhadrons,neutralhadrons,photons,muons,and electrons.

Electronsarereconstructedwithin thegeometrical acceptance, |ηe|<2.5,andfortransverse momentum pe

T>7 GeV.The

recon-struction combines the information from clusters of energy de-positsinthe ECALandthe trajectory inthe tracker[24]. Particle

trajectoriesinthetrackervolume arereconstructedusinga mod-eling ofthe electron energylossand fittedwitha Gaussian sum filter [25]. The contribution of the ECAL energy deposits to the electron transverse momentum measurement andits uncertainty are determined via a multivariate regression approach. Electron identificationreliesonamultivariatetechniquethatcombines ob-servables sensitive to the amount of bremsstrahlung along the electrontrajectory, the geometricalandmomentummatching be-tween the electron trajectory and associated clusters, aswell as showershapeobservables.

Muons are reconstructed within |ηµ|< 2.4 and for pµ_T > 5 GeV [26]. The reconstruction combines information from both thesilicontrackerandthemuondetectors.ThePFmuonsare se-lected from among the reconstructed muon track candidates by applyingrequirementsonthetrackcomponentsinthemuon sys-temandmatchingwithminimumionizingparticleenergydeposits inthecalorimeters.

For τ leptons, two principal decay modes are distinguished: a leptonic mode, τℓ, with a final state including either an elec-tron or a muon, anda hadronic mode, τh, witha final state

in-cludinghadrons. ThePFparticles areusedto reconstruct τh with

the“hadron-plus-strip”algorithm[27],whichoptimizesthe recon-struction and identification of specific τh decay modes. The π0

componentsofthe τhdecaysarefirstreconstructedandthen

com-bined with charged hadrons to reconstruct the τh decay modes.

Caseswhere τhincludesthreechargedhadronsarealsoincluded.

The missing transverse energy that is associated with neutrinos from τ decaysisignoredinthereconstruction. The τh candidates

inthisanalysisarerequiredtohave|ητh_{|<2.3 and p}τh

T >20 GeV.

Theisolationofindividualelectronsormuonsismeasured rel-ative to their transverse momentum pℓ

T, by summing over the

transverse momenta of charged hadrons andneutral particles in aconewith+R="(+η)2+ (+φ)2=0.4 aroundthelepton direc-tionattheinteractionvertex:

Rℓ

Iso=

#$

pcharged_T

+MAX%0,$pneutral_T +$pγ_T −ρ×Aeff

&' /pℓ

T. (1)

The (pcharged_T is the scalar sum of the transverse momenta of chargedhadronsoriginatingfromtheprimaryvertex.Theprimary vertexis chosen asthe vertexwiththe highestsumof p2

T ofits

constituent tracks. The (pneutral

T and (pγT are the scalar sums

of the transverse momenta forneutral hadrons andphotons, re-spectively. The average transverse-momentum flow density ρ is calculatedineacheventusinga“jetarea”[28],where ρ isdefined as the median of the pjet_T /Ajet distribution for all pileup jets in

theevent.Theeffectivearea Aeffisthegeometricarea ofthe

iso-lationcone timesan η-dependentcorrection factorthat accounts for the residualdependence of the isolation on pileup. Electrons andmuons areconsidered isolated if Rℓ

Iso<0.4. Allowing τ

lep-tons in the final state increases the background contamination, thereforetighter isolationrequirementsare imposedforelectrons andmuonsinZZ→ ℓℓτ τ decays: Rℓ

Iso<0.25 forZ→τℓ+τℓ−,and Re

Iso<0.1 forZ→τeτh,andRµIso<0.15 for τµτh.

The isolation of the τh is calculatedas the scalarsum ofthe

transversemomenta ofthechargedhadronsandneutralparticles inaconeof+R=0.5 aroundthe τhdirectionreconstructedatthe

interactionvertex.The τhisolationincludesacorrectionforpileup

effects,whichisbasedonthescalarsumoftransversemomentaof chargedparticlesnotassociatedwiththeprimaryvertexinacone of+R=0.8 aboutthe τh candidatedirection(pPU_T ). Theisolation

IPF₌#$pcharged_T

+MAX%0,$pneutral_T +$pγ_T − f×pPU_T &', (2)

wherethescalefactorof f₌0.0729,whichisusedinestimating the contribution to the isolation sum from neutral hadrons and photons, accounts for the difference in the neutral and charged contributionsandintheconesizes.Twostandardworkingpoints aredefinedbasedonthevalue oftheisolation sumcorrected for the pileup contribution: IPF_{<1(8)GeV for final states including}

one(two) τhcandidates.

TheelectronandmuonpairsfromZ-bosondecaysarerequired tooriginatefromtheprimaryvertex.Thisisensuredbydemanding that the significance of the three-dimensional impact parameter relative to the event vertex, SIP3D, satisfies SIP3D= |_σIP_IP|<4 for eachlepton.TheIP isthedistanceofclosestapproachofthelepton tracktotheprimaryvertexand σIPisitsassociateduncertainty.

Thecombinedefficiencies ofreconstruction,identification, and isolationofprimaryelectronsormuonsaremeasuredindatausing a“tag-and-probe”technique[29]appliedtoaninclusivesampleof Z events.Themeasurementsareperformedinbinsofpℓ

Tand|ηℓ|.

TheefficiencyforselectingelectronsintheECALbarrel(endcaps) isabout70%(60%)for7<pe_T<10 GeV,85%(77%)atpe_T≃10 GeV, and95% (89%) for pe

T≥20 GeV.It is about85% inthe transition

region betweentheECAL barrelandendcaps (1.44<|η|<1.57), averagingover thewhole pT range.The muonsarereconstructed

and identified with an efficiency greater than ∼98% in the full |ηµ|<2.4 range.The τhreconstructionefficiencyisapproximately

50%[27].

Final-state radiation (FSR) may affect the measured four-momentum of the leptons if it is not properly included in the reconstruction.Forelectrons,asignificantportionoftheFSR pho-tonsis included in the reconstructed energy becauseof the size of the electromagnetic clusters, but for muons additional treat-ment ofthe FSRphotonsis important.All photonsreconstructed within|ηµ_{|<2.4 areconsideredaspossibleFSRcandidatesifthey} haveatransversemomentumpγ_T >2(4)GeV andarefoundwithin +R<0.07(0.07< +R<0.5)fromtheclosestselectedlepton can-didate and are isolated. The photon isolation observable Rγ_Iso is the sum ofthe transverse momenta ofcharged hadrons, neutral hadrons, andphotons in a cone of +R=0.3 around the candi-datephotondirection,dividedby pγ_T.Isolatedphotonsmustsatisfy Rγ_Iso<1.TherecoveredFSRphotonisincludedinthelepton four-momentumandtheleptonisolationisthenrecalculatedwithout it. The performance of theFSR selection algorithm hasbeen de-termined using simulated samples, and the rate is verified with the Z and ZZ events in data.The photons within the acceptance fortheFSRselectionarereconstructedwithanefficiencyofabout 50%andwithameanpurityof80%.TheFSRphotonsarerecovered in0.5(5)%ofinclusiveZ eventswithelectron(muon)pairs.

4. Event selection

The data sample used inthis analysisis selected by the trig-gersystem, whichrequires thepresence ofapair ofelectrons or muons,oratripletofelectrons.Triggersrequiringanelectronand a muon are also used. For the double-lepton triggers, the high-est pT and the second-highest pT leptons are required to have

pT greater than 17and 8 GeV, respectively, whilefor the

triple-electron trigger the thresholdsare 15,8, and5 GeV. The trigger efficiencyfor ZZ events within the acceptance ofthis analysisis greater than 98%. The use of the triple-electron trigger with a looser pT requirementhelpstorecover1–2%ofthesignal events,

whileformuonssuchcontributionwasfoundtobenegligible.

InselectedZZ events,theZ candidatewiththemassclosestto theZ-bosonmassisdenotedZ1 andtheother one,Z2.The

selec-tionisdesignedtogivemutuallyexclusivesetsofsignalcandidates firstselectingZZ decaysto4e,4µ,and2e2µ,inthefollowing de-notedℓℓℓ′′ℓ′′;theseeventsarenotconsideredinZZ→ ℓℓτ τ chan-nel. The leptons are identified andisolated as described in Sec-tion3.WhenbuildingtheZ candidates,theFSRphotonsare kept if|mℓℓγ−mZ|<|mℓℓ−mZ|andmℓℓγ<100 GeV.Inthefollowing, the presenceof thephotonsin theℓℓℓ′′ℓ′′ kinematics isimplicit. TheleptonsconstitutingaZ candidatearerequiredtobethesame flavorandtohaveoppositecharges(ℓ+ℓ−).Thepairisretainedif itsatisfies60<mZ<120 GeV.IfmorethanoneZ2 candidate

sat-isfies all criteria, the ambiguity is resolved by choosing the pair ofleptons withthehighestscalarsumof pT.Amongthefour

se-lectedleptonsformingtheZ1 andtheZ2,atleastoneshouldhave

pT>20 GeV and anotherone shouldhavepT>10 GeV.These pT

thresholds ensure that the selected events have leptons with pT

valuesonthehigh-efficiencyplateauforthetrigger.

Fortheℓℓτ τ final state,eventsarerequiredtohaveone Z1→

ℓ+ℓ− candidate with pT>20 GeV for one of the leptons and

pT>10 GeV for theother lepton,anda Z2→τ+τ−,with τ

de-caying into τe, τµ, or τh. The leptons from the τℓ decays are required tohave pℓ

T>10 GeV. The τh candidates arerequired to

havepτh

T >20 GeV.TheFSRrecoveryisnotappliedtotheℓℓτ τ

fi-nalstates,sinceitdoesnotimprovethemassreconstruction.The invariant massofthereconstructedZ1 isrequiredtosatisfy 60<

mℓℓ<120 GeV,andthatoftheZ2tosatisfymmin<mττ<90 GeV,

wheremmin=20 GeV forZ2→τeτµ finalstatesand30 GeVforall others.

5. Background estimation

The lepton identificationand isolation requirementsdescribed in Section 3 significantly suppress all background contributions, andtheremnantportionofthemarisemainlyfromtheZ andWZ productioninassociationwithjets,aswellastt.Inallthesecases, a jetora non-promptlepton ismisidentifiedasan isolatede, µ,

τh, τe,or τµ.Leptons producedin thedecayof Z bosonsare re-ferredtoaspromptleptons;leptonsfrome.g.heavymesondecays are non-prompt. The requirements to eliminate non-prompt lep-tonsalsoremovehadronsthatappeartobeleptons.

Toestimate theexpectednumberofbackgroundeventsinthe signalregion,controldatasamplesaredefinedforeachlepton fla-vorcombinationℓ′ℓ′.The e and τe,and µ and τµ areconsidered asdifferentflavors,sincetheyoriginatefromdifferentparticles.

The control datasamplesforthe backgroundestimate are ob-tainedbyselectingeventscontainingZ1,whichpassesallselection

requirements,andtwoadditionalleptoncandidatesℓ′ℓ′.The addi-tionallepton pairmusthaveoppositecharge andmatchingflavor (e±_e∓_{, µ}±_µ∓_{, τ}±_τ∓_{). Control data samples enriched with Z+X} events, whereX stands forbb, cc, gluon, or light quark jets, are obtained by requiring that both additional leptons pass only re-laxedidentificationcriteriaandarerequiredtobenotisolated.By requiring one of the additional leptons to pass the full selection requirements,one obtainsdatasamplesenriched withWZ events andsignificantnumberoftt events.Theexpectednumberof back-groundeventsinthesignalregionforeachflavorpairisobtained by scalingthenumberofobservedZ1+ ℓ′ℓ′ eventsby thelepton misidentification probability and combiningthe results forZ+X andWZ,tt controlregionstogether.Theprocedureisidenticalfor allleptonflavors.

The misidentificationprobability,i.e., theprobability fora lep-toncandidatethatpassestherelaxedrequirementstopassthefull selection,ismeasuredseparately foreach flavorfromasampleof Z1+ ℓcandidateeventswitharelaxedidentificationandnoisolation

Table 1

TheexpectedyieldsofZZ andbackgroundevents,aswellastheirsum(“Totalexpected”)arecomparedwiththeobservedyieldsforeachdecaychannel.Thestatisticaland systematicuncertaintiesarealsoshown.

Decay channel Expected ZZ yield Background Total expected Observed 4e 55.28±0.25±7.64 2.16±0.26±0.88 57.44±0.37±7.69 54 4µ 77.32±0.29±10.08 1.19±0.36±0.48 78.51±0.49±10.09 75 2e2µ 136.09±0.59±17.50 2.35±0.34±0.93 138.44±0.70±17.52 148 eeτhτh 2.46±0.03±0.32 3.46±0.34±1.04 5.92±0.36±1.15 10 µµτhτh 2.80±0.03±0.34 3.89±0.37±1.17 6.69±0.39±1.30 10 eeτeτh 2.79±0.03±0.36 3.87±1.26±1.16 6.66±1.34±1.29 9 µµτeτh 2.87±0.03±0.37 1.49±0.67±0.60 4.36±0.71±0.73 2 eeτµτh 3.27±0.03±0.42 1.47±0.41±0.44 4.74±0.43±0.63 2 µµτµτh 3.81±0.03±0.50 1.55±0.43±0.46 5.36±0.46±0.70 5 eeτeτµ 2.23±0.03±0.29 3.04±1.32±1.50 5.27±1.40±1.61 4 µµτeτµ 2.41±0.03±0.32 0.74±0.51±0.37 3.15±0.54±0.51 5 Totalℓℓτ τ 22.65±0.05±2.94 19.51±2.15±5.85 42.16±2.28±6.87 47

Fig. 1. Distributionofthereconstructedfour-leptonmassforthe(upperleft)4e,(upperright)4µ,(lowerleft)2e2µ,and(lowerright)combinedℓℓτ τ decaychannels. Thedatasamplecorrespondstoanintegratedluminosityof19.6 fb−1_{.Pointsrepresentthedata,theshadedhistogramslabeledZZ representthe powheg+gg2zz+pythia}

predictionsforZZ signal,thehistogramslabeledWZ/Z+jets showthebackground,whichisestimatedfromdata,asdescribedinthetext.

requirementsontheℓcandidate.Themisidentificationprobabilityfor

eachleptonflavorisdefinedastheratioofthenumberofleptons thatpassthefinalisolation andidentificationrequirementstothe totalnumber ofleptons inthe sample. It is measured inbins of lepton pT and η.The contamination fromWZ events,whichmay

leadtoanoverestimateofthemisidentificationprobabilitybecause ofthe presence ofgenuine isolated leptons, issuppressed by re-quiringthat themeasured missingtransverse energyis lessthan 25 GeV.

Theestimatedbackgroundcontributionstothesignalregionare summarizedinTable 1.Theprocedure excludesapossibledouble

countingduetoZ+X eventsthatcanbefoundintheWZ control region.AcorrectionforthesmallcontributionofZZ eventsinthe control region is applied based on MC simulation. The predicted backgroundyieldhasa smalleffectontheZZ cross section mea-surementintheℓℓℓ′′ℓ′′ channels, butiscomparabletothesignal yieldforthecaseofℓℓτ τ.

6. Systematic uncertainties

The systematic uncertainties for trigger efficiency (1.5%) are evaluated fromdata.Theuncertainties arisingfromlepton

identi-Fig. 2. (upper left)Distributionofthereconstructedfour-leptonmassfor thesumofthe 4e,4µ, and2e2µdecaychannels.(upper right)ReconstructedZ1 mass. The

correlationbetweenthereconstructedZ1andZ2massesforthe(lower left)combined4e,4µ,and2e2µfinalstatesand(lower right)forℓℓτ τfinalstates.Pointsrepresent thedata,theshadedhistogramslabeledZZ representthe powheg+gg2zz+pythia predictionsforZZ signal,thehistogramslabeledWZ/Z+jets showbackground,whichis estimatedfromdata,asdescribedinthetext.

ficationandisolationare1–2%formuonsandelectrons,and6–7% for τh.TheuncertaintyintheLHCintegratedluminosityofthedata

sampleis2.6%[30].

Theoretical uncertainties in the ZZ→ ℓℓℓ′′_ℓ′′ _{acceptance are} evaluatedusing mcfm andbyvaryingtherenormalizationand fac-torizationscales,upanddown,byafactoroftwowithrespectto thedefaultvalues µR=µF=mZ.Thevariationsintheacceptance

are0.1%(NLOqq→ZZ)and0.4%(gg→ZZ),andcanbeneglected. UncertaintiesrelatedtothechoiceofthePDFandthestrong cou-pling constant αs are evaluated followingthe PDF4LHC [31]

pre-scriptionandusingCT10, MSTW08,andNNPDF[32] PDFsetsand foundtobe4%(NLOqq→ZZ)and5%(gg→ZZ).

TheuncertaintiesinZ+jets,WZ+jets,andtt yieldsreflectthe uncertaintiesinthemeasuredvaluesofthemisidentificationrates andthe limited statistics of the control regions in the data, and varybetween20%and70%.

The uncertainty in the unfolding procedure discussed in Sec-tion7arisesfromdifferencesbetween sherpa and powheg forthe unfoldingfactors(2–3%),fromscaleandPDFuncertainties(4–5%), andfromexperimentaluncertainties(4–5%).

7. The ZZ cross section measurement

Themeasuredandexpectedeventyieldsforalldecaychannels are summarized in Table 1. The recently discovered Higgs parti-clewiththemassof125 GeVdoesnotcontributetothisanalysis asbackgroundbecauseofthephasespaceselection requirements.

The reconstructedfour-lepton invariantmassdistributions forthe 4e, 4µ,2e2µ,andcombined ℓℓτ τ decaychannels are shownin Fig. 1.Theshapeofthebackgroundistakenfromdata.The recon-structed four-lepton invariant massdistributionfor thecombined 4e, 4µ,and2e2µ channelsisshownin Fig. 2(upper left).Fig. 2 (upper right) presents the invariant mass of the Z1 candidates.

Figs. 2(lowerleft)and(lowerright)showthecorrelationbetween the reconstructed Z1 and Z2 massesfor (lowerleft) 4e, 4µ,and

2e2µ and for (lower right) ℓℓτ τ final states. The data are well reproduced bythesignalsimulationandwithbackground predic-tionsestimatedfromdata.

The measuredyieldsare usedtoevaluatethetotalZZ produc-tion cross section. The signal acceptance is evaluated from sim-ulation andcorrected for each individual lepton flavor inbins of pT and η using factors obtained with the “tag-and-probe”

tech-nique. The requirements on pT and η for the particles in the

final state reduce the full possible phase space of the ZZ→4ℓ measurement by a factorwithin a rangeof0.56–0.59 forthe 4e, 4µ, and 2e2µ, depending on the final state, and by a factor of 0.18–0.21fortheℓℓτ τ finalstates,withrespecttoallevents gen-eratedinthemasswindow60<mZ1,mZ2<120 GeV.The

branch-ing fraction for Z→ ℓ′_ℓ′ _{is (3.3658±0.0023)% for each lepton} flavor[33].

Toincludeallfinal statesinthecrosssectioncalculation, a si-multaneous fit to the number of observed events in all decay channelsisperformed.Thelikelihoodiswrittenasacombination of individual channel likelihoods for the signal and background

Table 2

ThetotalZZ productioncrosssectionasmeasuredineachdecaychannelandfor thecombinationofallchannels.

Decay channel Total cross section, pb 4e 7.2+1.0

−0.9(stat)+−00..56(syst)±0.4(theo)±0.2 (lumi)

4µ 7.3+0.8

−0.8(stat)+−00..56(syst)±0.4(theo)±0.2 (lumi)

2e2µ 8.1+0.7

−0.6(stat)+−00..56(syst)±0.4(theo)±0.2 (lumi)

ℓℓτ τ 7.7+2.1

−1.9(stat)+−21..80(syst)±0.4(theo)±0.2 (lumi)

Combined 7.7±0.5 (stat)₋+0_0..5₄(syst)±0.4(theo)±0.2 (lumi) hypotheses,with systematical uncertainties used asnuisance pa-rametersinthefit.Each τ-leptondecaymode,listedinTable 1,is treatedasaseparatechannel.

Table 2 lists the total cross section obtained from each in-dividual decay channel as well as the total cross section based on the combination of all channels. The measured cross section agrees withthe theoretical value of7.7±0.6 pb calculated with mcfm 6.0. In this calculation, the contribution from qq→ZZ is

obtained at NLO, while the smaller contribution (approximately 6%)fromgg→ZZ isobtainedatLO. TheMSTW2008PDFisused andtherenormalizationandfactorizationscalessetto µR=µF=

91.2 GeV.

The measurement of the differential cross sections is an im-portantpartofthisanalysis,sinceitprovidesdetailedinformation aboutZZ kinematics.Threedecaychannels, 4e,4µ,and2e2µ,are combined, since their kinematic distributions are the same; the ℓℓτ τ channel is not included. The observed yields are unfolded usingthemethoddescribedinRef.[34].

The differential distributions normalized to the fiducial cross sectionsarepresentedinFigs. 3 and4forthecombinationofthe 4e, 4µ,and 2e2µdecay channels. Thefiducial crosssection def-inition includes pℓ

T and |ηℓ| selections on each lepton, and the

60–120 GeV mass requirement, as described in Section 4. Fig. 3 showsthedifferentialcrosssectionsinbinsof pT for:(upper left)

the highest-pT lepton in the event, (upper right) the Z1, and

(lower left) the ZZ system. Fig. 3(lower left) showsthe normal-izeddσ/dmZZ distribution.Thedataarecorrectedforbackground

contributionsandcomparedwiththetheoreticalpredictionsfrom

Fig. 3. Differentialcrosssectionsnormalizedtothefiducialcrosssectionforthecombined4e,4µ,and2e2µdecaychannelsasafunctionofpTfor(upperleft)thehighest

pTleptonintheevent,(upperright)theZ1,and(lowerleft)theZZ system.Figure(lowerright)showsthenormalizeddσ/dmZZdistribution.Pointsrepresentthedata,and

theshadedhistogramslabeledZZ representthe powheg+gg2zz+pythia predictionsforZZ signal,whilethesolidcurvescorrespondtoresultsofthe mcfm calculations.The bottompartofeachsubfigurerepresentstheratioofthemeasuredcrosssectiontotheexpectedonefrom powheg+gg2zz+pythia (blackcrosseswithsolidsymbols)and mcfm (redcrosses).Theshadedareasonalltheplotsrepresentthefulluncertaintiescalculatedasthequadraturesumofthestatisticalandsystematicuncertainties,whereas thecrossesrepresentthestatisticaluncertaintiesonly.(Forinterpretationofthereferencestocolorinthisfigurelegend,thereaderisreferredtothewebversionofthis article.)

Fig. 4. Differentialcrosssectionnormalizedtothefiducialcrosssectionforthe com-bined4e,4µ,and2e2µdecaychannelsasafunctionof(top)azimuthalseparation ofthetwoZ bosonsand(bottom)+RbetweentheZ-bosons.Pointsrepresentthe data,andtheshadedhistogramslabeledZZ representthe powheg+gg2zz+pythia predictionsforZZ signal,whilethesolidcurvescorrespondtoresultsofthe mcfm calculations.Thebottompartofeachsubfigurerepresentstheratioofthemeasured crosssectiontotheexpectedonefrom powheg+gg2zz+pythia (blackcrosseswith solidsymbols)and mcfm (redcrosses).Theshadedareasonalltheplots repre-sentthefulluncertaintiescalculatedasthequadraturesumofthestatisticaland systematicuncertainties,whereasthecrossesrepresentthestatisticaluncertainties only.(Forinterpretationofthereferencestocolorinthisfigurelegend,thereader isreferredtothewebversionofthisarticle.)

powheg and mcfm. Thebottompartofeach plotshowsthe ratio ofthemeasuredtothepredictedvalues.Thebinsizeswerechosen accordingtotheresolutionoftherelevantvariables,tryingalsoto keepthestatisticaluncertainties atasimilarlevelforall thebins. Fig. 4showstheangularcorrelationsbetweenZ bosons,whichare ingoodagreementwiththeMC simulations.Some difference be-tween powheg and mcfm calculationsappears atvery low pT of

theZZ systemandforazimuthal separationoftheZ bosons close to π.Thisregionisbettermodeledby powheg interfacedwiththe pythia partonshowerprogram.

8. Limits on anomalous triple gauge couplings

The presence of ATGCs would be manifested as an increased yieldofeventsathighfour-leptonmasses.Fig. 5presentsthe dis-tributionof thefour-lepton reconstructed mass,whichis usedto setthe limits, forthecombined 4e, 4µ,and2e2µ channels. The shadedhistogramrepresentstheresultsofthe powheg simulation

Fig. 5. Distributionofthefour-leptonreconstructedmassforthecombined4e,4µ, and 2e2µchannels. Pointsrepresentthe data,the shadedhistogram labeledZZ representsthe powheg+gg2zz+pythia predictionsforZZ signal,thehistograms la-beledWZ/Z+jets showsbackground,whichisestimatedfromdata,asdescribedin thetext.Thedashedanddottedhistogramsindicatetheresultsofthe sherpa simu-lationfortheSM( fZ

4=0)andinthepresenceofanATGC( f4Z=0.015)withallthe

otheranomalouscouplingssettozero.Thelastbinincludesallentrieswithmasses above1000 GeV.

forthe ZZ signal,andthedashed line, whichagreeswell withit, is the prediction of sherpa for f₄Z=0 normalized to the mcfm crosssection. Thedottedlineindicatesthe sherpa predictionsfor a specific ATGC value ( fZ

4 =0.015) with all theother anomalous

couplingssettozero.

The invariant mass distributions are interpolated from the sherpa simulationfordifferentvaluesoftheanomalouscouplings in the range between 0 and 0.015. For each distribution, only one or two couplings arevaried whileall others are setto zero. The measured signal is obtained from a comparison of the data to a grid of ATGC models in the (f₄Z,f₄γ) and (f₅Z,f₅γ) param-eter planes. Expected signal values are interpolated between the 2D grid points usingasecond-degreepolynomial, sincethe cross section for signaldepends quadraticallyonthe coupling parame-ters.A profilelikelihoodmethod[33] isusedtoderivethe limits. Systematic uncertainties are taken into account by varying the numberofexpectedsignalandbackgroundeventswithintheir un-certainties.Noformfactorisusedwhenderivingthelimitssothat the results do not depend on any assumedenergy scale charac-terizing newphysics.The constraintsonanomalouscouplings are displayed in Fig. 6. The curves indicate 68% and95% confidence levels, andthe solid dot shows where the likelihood reaches its maximum. Coupling values outside the contours are excluded at the corresponding confidencelevels.The limitsaredominated by statisticaluncertainties.

One-dimensional 95% CLlimitsfor the f₄Z,γ and f₅Z,γ anoma-louscouplingparametersare:

−0.004< f₄Z<0.004, −0.004< f₅Z<0.004, −0.005< f₄γ <0.005, −0.005< f₅γ <0.005.

Intheone-dimensionalfits,alloftheATGCparametersexceptthe oneunderstudyaresettozero.ThesevaluesextendpreviousCMS results on vector boson self-interactions [3]and improve on the previous limitsby factors of threeto four, they are presented in Fig. 6ashorizontalandverticallines.

Fig. 6. Two-dimensionalexclusionlimitsat 68%(dashedcontour)and 95%(solid contour)CLontheZZZ andZZγ ATGCs.Thetop(bottom)plotshowsthe exclu-sioncontourinthe(fZ

4(5),f γ

4(5))parameterplanes.Thesoliddotshowswherethe

likelihoodreachesitsmaximum.Thevaluesofcouplingsoutside ofcontours are excludedatthecorrespondingconfidencelevel.Thelinesinthemiddlerepresent one-dimensionallimits.Noformfactorisused.

9. Summary

MeasurementshavebeenpresentedoftheinclusiveZZ produc-tioncrosssectioninproton–protoncollisionsat8 TeVintheZZ→ ℓℓℓ′ℓ′decaymode,withℓ=e, µandℓ′=e, µ, τ.Thedatasample corresponds to an integrated luminosity of 19.6 fb−1. The mea-suredtotalcrosssection σ(pp→ZZ)=7.7±0.5 (stat)+₋0₀._.5₄(syst)± 0.4 (theo)±0.2 (lumi) pb for both Z bosons in the mass range 60<mZ<120 GeV and the differentialcross sectionsagree well withtheSM predictions. Improved limitsonanomalous ZZZ and ZZγ triplegaugecouplingsareestablished,significantlyrestricting theirpossibleallowedranges.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technicalandadministrativestaffs atCERN andatother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentresand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythecomputinginfrastructure essential toour analyses. Finally, we acknowledge the enduring support for the construc-tionandoperationofthe LHCandtheCMSdetectorprovided by thefollowingfundingagencies:BMWFWandFWF(Austria);FNRS

and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES(Bulgaria);CERN;CAS,MoST,andNSFC(China);COLCIENCIAS (Colombia);MSESandCSF(Croatia);RPF(Cyprus);MoER,ERCIUT andERDF(Estonia);Academy ofFinland,MEC,andHIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Republic of Korea); LAS (Lithuania); MOE and UM (Malaysia); CINVESTAV, CONACYT,SEP,andUASLP-FAI(Mexico);MBIE(NewZealand);PAEC (Pakistan);MSHEandNSC (Poland);FCT(Portugal);JINR(Dubna); MON,RosAtom,RASandRFBR(Russia);MESTD(Serbia);SEIDIand CPAN(Spain);SwissFundingAgencies(Switzerland);MST(Taipei); ThEPCenter,IPST, STARandNSTDA(Thailand);TUBITAKandTAEK (Turkey);NASUandSFFR(Ukraine); STFC(United Kingdom);DOE andNSF(USA).

Individuals have received support from the Marie-Curie pro-gramme and the European Research Council and EPLANET (Eu-ropean 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 Recherchedansl’Industrieetdansl’Agriculture(FRIA-Belgium);the AgentschapvoorInnovatiedoorWetenschapenTechnologie (IWT-Belgium); theMinistry ofEducation, YouthandSports (MEYS) of theCzechRepublic;theCouncilofScienceandIndustrialResearch, India; the HOMING PLUS programme of Foundation For Polish Science, cofinanced from European Union, Regional Development Fund; the Compagnia di San Paolo (Torino); and the Thalis and AristeiaprogrammescofinancedbyEU-ESFandtheGreekNSRF.

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CMS Collaboration

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

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam, T. Bergauer, M. Dragicevic,J. Erö, C. Fabjan1,M. Friedl, R. Frühwirth1,V.M. Ghete, C. Hartl,

N. Hörmann, J. Hrubec, M. Jeitler1_{, W. Kiesenhofer,V. Knünz, M. Krammer}1_{, I. Krätschmer,D. Liko,}

I. Mikulec,D. Rabady2, B. Rahbaran, H. Rohringer,R. Schöfbeck, J. Strauss,A. Taurok,

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

InstitutfürHochenergiephysikderOeAW,Wien,Austria

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

NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus

S. Alderweireldt, M. Bansal, S. Bansal, T. Cornelis,E.A. De Wolf,X. Janssen, A. Knutsson,S. Luyckx,

S. Ochesanu,B. Roland, R. Rougny, M. Van De Klundert, H. Van Haevermaet,P. Van Mechelen,

N. Van Remortel,A. Van Spilbeeck

UniversiteitAntwerpen,Antwerpen,Belgium

F. Blekman, S. Blyweert,J. D’Hondt, N. Daci,N. Heracleous, A. Kalogeropoulos, J. Keaveney,T.J. Kim,

S. Lowette,M. Maes, A. Olbrechts, Q. Python, D. Strom, S. Tavernier,W. Van Doninck, P. Van Mulders,

G.P. Van Onsem,I. Villella

VrijeUniversiteitBrussel,Brussel,Belgium

C. Caillol, B. Clerbaux, G. De Lentdecker, D. Dobur, L. Favart, A.P.R. Gay, A. Grebenyuk,A. Léonard,

A. Mohammadi, L. Perniè2_{, T. Reis,T. Seva, L. Thomas, C. Vander Velde, P. Vanlaer, J. Wang}

UniversitéLibredeBruxelles,Bruxelles,Belgium

V. Adler,K. Beernaert, L. Benucci, A. Cimmino,S. Costantini, S. Crucy, S. Dildick,A. Fagot, G. Garcia,

F. Thyssen,M. Tytgat, E. Yazgan, N. Zaganidis

GhentUniversity,Ghent,Belgium

S. Basegmez, C. Beluffi3, G. Bruno,R. Castello, A. Caudron, L. Ceard, G.G. Da Silveira,C. Delaere,

T. du Pree,D. Favart,L. Forthomme, A. Giammanco4_{,J. Hollar, P. Jez, M. Komm,V. Lemaitre, J. Liao,}

C. Nuttens, D. Pagano,A. Pin, K. Piotrzkowski,A. Popov5,L. Quertenmont, M. Selvaggi, M. Vidal Marono,

J.M. Vizan Garcia

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

N. Beliy,T. Caebergs, E. Daubie, G.H. Hammad

UniversitédeMons,Mons,Belgium

G.A. Alves,M. Correa Martins Junior,T. Dos Reis Martins, M.E. Pol

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

W.L. Aldá Júnior, W. Carvalho,J. Chinellato6, A. Custódio, E.M. Da Costa, D. De Jesus Damiao,

C. De Oliveira Martins, S. Fonseca De Souza, H. Malbouisson,M. Malek, D. Matos Figueiredo, L. Mundim,

H. Nogima,W.L. Prado Da Silva, J. Santaolalla, A. Santoro, A. Sznajder,E.J. Tonelli Manganote6,

A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

C.A. Bernardesb_{, F.A. Dias}a,7_{, T.R. Fernandez Perez Tomei}a_{,E.M. Gregores}b_{,P.G. Mercadante}b_,

S.F. Novaesa, Sandra S. Padulaa

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

A. Aleksandrov, V. Genchev2_{, P. Iaydjiev, A. Marinov,S. Piperov, M. Rodozov,G. Sultanov, M. Vutova}

InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria

A. Dimitrov,I. Glushkov, R. Hadjiiska, V. Kozhuharov,L. Litov, B. Pavlov,P. Petkov

UniversityofSofia,Sofia,Bulgaria

J.G. Bian,G.M. Chen, H.S. Chen, M. Chen, R. Du,C.H. Jiang, D. Liang,S. Liang,R. Plestina8_{, J. Tao,}

X. Wang,Z. Wang

InstituteofHighEnergyPhysics,Beijing,China

C. Asawatangtrakuldee, Y. Ban,Y. Guo, Q. Li, W. Li, S. Liu,Y. Mao, S.J. Qian, D. Wang,L. Zhang, W. Zou

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

C. Avila,L.F. Chaparro Sierra, C. Florez, J.P. Gomez, B. Gomez Moreno,J.C. Sanabria

UniversidaddeLosAndes,Bogota,Colombia

N. Godinovic, D. Lelas,D. Polic, I. Puljak

TechnicalUniversityofSplit,Split,Croatia

Z. Antunovic,M. Kovac

UniversityofSplit,Split,Croatia

V. Brigljevic,K. Kadija, J. Luetic,D. Mekterovic, L. Sudic

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

UniversityofCyprus,Nicosia,Cyprus

M. Bodlak,M. Finger, M. Finger Jr.

CharlesUniversity,Prague,CzechRepublic

Y. Assran9, A. Ellithi Kamel10,M.A. Mahmoud11, A. Radi12,13

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

M. Kadastik, M. Murumaa, M. Raidal, A. Tiko

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola, G. Fedi,M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

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

P. Luukka, T. Mäenpää,T. Peltola, E. Tuominen, J. Tuominiemi,E. Tuovinen, L. Wendland

HelsinkiInstituteofPhysics,Helsinki,Finland

T. Tuuva

LappeenrantaUniversityofTechnology,Lappeenranta,Finland

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

A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry,E. Locci, J. Malcles,A. Nayak, J. Rander,

A. Rosowsky, M. Titov

DSM/IRFU,CEA/Saclay,Gif-sur-Yvette,France

S. Baffioni,F. Beaudette, P. Busson, C. Charlot, T. Dahms, M. Dalchenko,L. Dobrzynski, N. Filipovic,

A. Florent,R. Granier de Cassagnac, L. Mastrolorenzo, P. Miné, C. Mironov, I.N. Naranjo, M. Nguyen,

C. Ochando, P. Paganini, R. Salerno,J.B. Sauvan, Y. Sirois, C. Veelken, Y. Yilmaz,A. Zabi

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

J.-L. Agram14_{, J. Andrea, A. Aubin, D. Bloch,J.-M. Brom, E.C. Chabert,C. Collard, E. Conte}14_,

J.-C. Fontaine14,D. Gelé, U. Goerlach, C. Goetzmann,A.-C. Le Bihan, P. Van Hove

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

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,N. Beaupere, G. Boudoul2,S. Brochet, C.A. Carrillo Montoya, J. Chasserat, R. Chierici,

D. Contardo2_{, P. Depasse,H. El Mamouni, J. Fan, J. Fay, S. Gascon, M. Gouzevitch, B. Ille, T. Kurca,}

M. Lethuillier, L. Mirabito,S. Perries, J.D. Ruiz Alvarez,D. Sabes,L. Sgandurra, V. Sordini,

M. Vander Donckt, P. Verdier, S. Viret,H. Xiao

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

Z. Tsamalaidze15

InstituteofHighEnergyPhysicsandInformatization,TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann, S. Beranek,M. Bontenackels, B. Calpas,M. Edelhoff, L. Feld, O. Hindrichs,

B. Wittmer, V. Zhukov5

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

M. Ata, J. Caudron,E. Dietz-Laursonn, D. Duchardt, M. Erdmann,R. Fischer,A. Güth, T. Hebbeker,

C. Heidemann,K. Hoepfner,D. Klingebiel, S. Knutzen,P. Kreuzer, M. Merschmeyer,A. Meyer,

M. Olschewski, K. Padeken,P. Papacz, H. Reithler,S.A. Schmitz,L. Sonnenschein, D. Teyssier,S. Thüer,

M. Weber

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

V. Cherepanov, Y. Erdogan,G. Flügge, H. Geenen, M. Geisler, W. Haj Ahmad, F. Hoehle,B. Kargoll,

T. Kress,Y. Kuessel, J. Lingemann2_{,A. Nowack, I.M. Nugent,L. Perchalla, O. Pooth, A. Stahl}

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

I. Asin,N. Bartosik, J. Behr,W. Behrenhoff, U. Behrens,A.J. Bell, M. Bergholz16_{,A. Bethani, K. Borras,}

A. Burgmeier,A. Cakir,L. Calligaris, A. Campbell, S. Choudhury, F. Costanza, C. Diez Pardos,S. Dooling,

T. Dorland,G. Eckerlin, D. Eckstein, T. Eichhorn, G. Flucke, J. Garay Garcia, A. Geiser, P. Gunnellini,

J. Hauk, G. Hellwig,M. Hempel, D. Horton, H. Jung, M. Kasemann,P. Katsas, J. Kieseler, C. Kleinwort,

D. Krücker,W. Lange, J. Leonard, K. Lipka,A. Lobanov, W. Lohmann16, B. Lutz,R. Mankel, I. Marfin,

I.-A. Melzer-Pellmann,A.B. Meyer, J. Mnich, A. Mussgiller, S. Naumann-Emme, O. Novgorodova,

F. Nowak,E. Ntomari,H. Perrey, D. Pitzl,R. Placakyte, A. Raspereza, P.M. Ribeiro Cipriano,E. Ron,

M.Ö. Sahin,J. Salfeld-Nebgen,P. Saxena, R. Schmidt16_{,T. Schoerner-Sadenius, M. Schröder, S. Spannagel,}

A.D.R. Vargas Trevino,R. Walsh, C. Wissing

DeutschesElektronen-Synchrotron,Hamburg,Germany

M. Aldaya Martin,V. Blobel, M. Centis Vignali, J. Erfle,E. Garutti, K. Goebel, M. Görner, M. Gosselink,

J. Haller, R.S. Höing,H. Kirschenmann, R. Klanner, R. Kogler,J. Lange, T. Lapsien, T. Lenz,I. Marchesini,

J. Ott, T. Peiffer, N. Pietsch,D. Rathjens, C. Sander, H. Schettler,P. Schleper, E. Schlieckau,A. Schmidt,

M. Seidel,J. Sibille17, V. Sola,H. Stadie, G. Steinbrück, D. Troendle,E. Usai, L. Vanelderen

UniversityofHamburg,Hamburg,Germany

C. Barth,C. Baus, J. Berger,C. Böser, E. Butz, T. Chwalek, W. De Boer,A. Descroix, A. Dierlamm,

M. Feindt,F. Hartmann2_{,T. Hauth}2_{, U. Husemann,I. Katkov}5_{,A. Kornmayer}2_{,E. Kuznetsova,}

P. Lobelle Pardo, M.U. Mozer,Th. Müller, A. Nürnberg,G. Quast, K. Rabbertz, F. Ratnikov,S. Röcker,

H.J. Simonis,F.M. Stober, R. Ulrich, J. Wagner-Kuhr,S. Wayand, T. Weiler, R. Wolf

InstitutfürExperimentelleKernphysik,Karlsruhe,Germany

G. Anagnostou,G. Daskalakis, T. Geralis,V.A. Giakoumopoulou, A. Kyriakis, D. Loukas,A. Markou,

C. Markou, A. Psallidas,I. Topsis-Giotis

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

L. Gouskos,A. Panagiotou, N. Saoulidou, E. Stiliaris

UniversityofAthens,Athens,Greece

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

UniversityofIoánnina,Ioánnina,Greece

G. Bencze,C. Hajdu, P. Hidas,D. Horvath18_{, F. Sikler,V. Veszpremi, G. Vesztergombi}19_{, A.J. Zsigmond}

WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni,S. Czellar, J. Karancsi20_{,J. Molnar, J. Palinkas, Z. Szillasi}

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

UniversityofDebrecen,Debrecen,Hungary

S.K. Swain

NationalInstituteofScienceEducationandResearch,Bhubaneswar,India

S.B. Beri, V. Bhatnagar,N. Dhingra, R. Gupta, A.K. Kalsi, M. Kaur, M. Mittal, N. Nishu, J.B. Singh

PanjabUniversity,Chandigarh,India

Ashok Kumar, Arun Kumar,S. Ahuja, A. Bhardwaj, B.C. Choudhary,A. Kumar, S. Malhotra,M. Naimuddin,

K. Ranjan,V. Sharma

UniversityofDelhi,Delhi,India

S. Banerjee, S. Bhattacharya, K. Chatterjee,S. Dutta, B. Gomber, Sa. Jain, Sh. Jain,R. Khurana, A. Modak,

S. Mukherjee,D. Roy, S. Sarkar, M. Sharan

SahaInstituteofNuclearPhysics,Kolkata,India

A. Abdulsalam, D. Dutta, S. Kailas,V. Kumar, A.K. Mohanty2_{, L.M. Pant, P. Shukla,A. Topkar}

BhabhaAtomicResearchCentre,Mumbai,India

T. Aziz, S. Banerjee, R.M. Chatterjee,R.K. Dewanjee, S. Dugad, S. Ganguly, S. Ghosh,M. Guchait,

A. Gurtu21, G. Kole, S. Kumar, M. Maity22,G. Majumder, K. Mazumdar, G.B. Mohanty, B. Parida,

K. Sudhakar, N. Wickramage23

TataInstituteofFundamentalResearch,Mumbai,India

H. Bakhshiansohi,H. Behnamian, S.M. Etesami24_{, A. Fahim}25_{, R. Goldouzian, A. Jafari,M. Khakzad,}

M. Mohammadi Najafabadi, M. Naseri, S. Paktinat Mehdiabadi, B. Safarzadeh26, M. Zeinali

InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran

M. Felcini,M. Grunewald

UniversityCollegeDublin,Dublin,Ireland

M. Abbresciaa,b_{, L. Barbone}a,b_{,C. Calabria}a,b_{,S.S. Chhibra}a,b_{,A. Colaleo}a_{,D. Creanza}a,c_,

N. De Filippisa,c_{, M. De Palma}a,b_{,L. Fiore}a_{,G. Iaselli}a,c_{,G. Maggi}a,c_{,M. Maggi}a_{, S. My}a,c_{, S. Nuzzo}a,b_,

N. Pacificoa_{,A. Pompili}a,b_{,G. Pugliese}a,c_{, R. Radogna}a,b,2_{,G. Selvaggi}a,b_{,L. Silvestris}a,2_{, G. Singh}a,b_,

R. Vendittia,b_{,P. Verwilligen}a_{, G. Zito}a

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

G. Abbiendia_{,A.C. Benvenuti}a_{,D. Bonacorsi}a,b_{, S. Braibant-Giacomelli}a,b_{, L. Brigliadori}a,b_,

R. Campaninia,b_{, P. Capiluppi}a,b_{,A. Castro}a,b_{,F.R. Cavallo}a_{, G. Codispoti}a,b_{, M. Cuffiani}a,b_,

G.M. Dallavallea_{,F. Fabbri}a_{, A. Fanfani}a,b_{, D. Fasanella}a,b_{,P. Giacomelli}a_{,C. Grandi}a_{,L. Guiducci}a,b_,

S. Marcellinia, G. Masettia,2_{,A. Montanari}a_{,F.L. Navarria}a,b_{, A. Perrotta}a_{,F. Primavera}a,b_{,A.M. Rossi}a,b_,

T. Rovellia,b_{,G.P. Siroli}a,b_{,N. Tosi}a,b_{,R. Travaglini}a,b

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

S. Albergoa,b_{,G. Cappello}a_{, M. Chiorboli}a,b_{, S. Costa}a,b_{, F. Giordano}a,2_{,R. Potenza}a,b_{, A. Tricomi}a,b_,

C. Tuvea,b

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

G. Barbaglia_{,V. Ciulli}a,b_{,C. Civinini}a_{, R. D’Alessandro}a,b_{, E. Focardi}a,b_{,E. Gallo}a_{, S. Gonzi}a,b_,

V. Goria,b,2_{,P. Lenzi}a,b_{,M. Meschini}a_{,S. Paoletti}a_{, G. Sguazzoni}a_{, A. Tropiano}a,b

a_{INFNSezionediFirenze,Firenze,Italy} b_{UniversitàdiFirenze,Firenze,Italy}

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

INFNLaboratoriNazionalidiFrascati,Frascati,Italy

F. Ferroa_{, M. Lo Vetere}a,b_{, E. Robutti}a_{,S. Tosi}a,b

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

M.E. Dinardoa,b_{, S. Fiorendi}a,b,2_{, S. Gennai}a,2_{,R. Gerosa}2_{, A. Ghezzi}a,b_{,P. Govoni}a,b_{,M.T. Lucchini}a,b,2_,

S. Malvezzia, R.A. Manzonia,b_{, A. Martelli}a,b_{, B. Marzocchi,D. Menasce}a_{,L. Moroni}a_{,M. Paganoni}a,b_,

D. Pedrinia,S. Ragazzia,b_{,N. Redaelli}a_{, T. Tabarelli de Fatis}a,b

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

S. Buontempoa, N. Cavalloa,c_{,S. Di Guida}a,d,2_{, F. Fabozzi}a,c_{,A.O.M. Iorio}a,b_{, L. Lista}a_{,S. Meola}a,d,2_,

M. Merolaa_{, P. Paolucci}a,2

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

P. Azzia, N. Bacchettaa, D. Biselloa,b_{, A. Branca}a,b_{,R. Carlin}a,b_{,P. Checchia}a_{, M. Dall’Osso}a,b_{, T. Dorigo}a_,

U. Dossellia_{,M. Galanti}a,b_{, F. Gasparini}a,b_{, U. Gasparini}a,b_{,P. Giubilato}a,b_{,A. Gozzelino}a_,

K. Kanishcheva,c_{,S. Lacaprara}a_{, M. Margoni}a,b_{, J. Pazzini}a,b_{, M. Pegoraro}a_{, N. Pozzobon}a,b_,

P. Ronchesea,b_{,F. Simonetto}a,b_{, M. Tosi}a,b_{,A. Triossi}a_{,S. Ventura}a_{,A. Zucchetta}a,b_{,G. Zumerle}a,b

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

M. Gabusia,b_{,S.P. Ratti}a,b_{, C. Riccardi}a,b_{,P. Salvini}a_{,P. Vitulo}a,b

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

M. Biasinia,b_{,G.M. Bilei}a_{,D. Ciangottini}a,b_{, L. Fanò}a,b_{,P. Lariccia}a,b_{,G. Mantovani}a,b_{, M. Menichelli}a_,

F. Romeoa,b_{,A. Saha}a_{,A. Santocchia}a,b_{, A. Spiezia}a,b,2

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

K. Androsova,27_{,P. Azzurri}a_{,G. Bagliesi}a_{,J. Bernardini}a_{,T. Boccali}a_{,G. Broccolo}a,c_{,R. Castaldi}a_,

M.A. Cioccia,27_{,R. Dell’Orso}a_{, S. Donato}a,c_{, F. Fiori}a,c_{, L. Foà}a,c_{,A. Giassi}a_{, M.T. Grippo}a,27_{, F. Ligabue}a,c_,

T. Lomtadzea, L. Martinia,b_{,A. Messineo}a,b_{,C.S. Moon}a,28_{,F. Palla}a,2_{,A. Rizzi}a,b_{,A. Savoy-Navarro}a,29_,

A.T. Serbana, P. Spagnoloa,P. Squillaciotia,27_{, R. Tenchini}a_{,G. Tonelli}a,b_{, A. Venturi}a_{, P.G. Verdini}a_,

C. Vernieria,c,2

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

c_{ScuolaNormaleSuperiorediPisa,Pisa,Italy}

L. Baronea,b_{, F. Cavallari}a_{,D. Del Re}a,b_{, M. Diemoz}a_{, M. Grassi}a,b_{,C. Jorda}a_{,E. Longo}a,b_{,F. Margaroli}a,b_,

P. Meridiania_{,F. Micheli}a,b,2_{,S. Nourbakhsh}a,b_{, G. Organtini}a,b_{,R. Paramatti}a_{, S. Rahatlou}a,b_,

C. Rovellia,F. Santanastasioa,b_{,L. Soffi}a,b,2_{, P. Traczyk}a,b

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

N. Amapanea,b_{, R. Arcidiacono}a,c_{,S. Argiro}a,b,2_{, M. Arneodo}a,c_{, R. Bellan}a,b_{, C. Biino}a_{,N. Cartiglia}a_,

S. Casassoa,b,2_{, M. Costa}a,b_{, A. Degano}a,b_{,N. Demaria}a_{,L. Finco}a,b_{,C. Mariotti}a_{, S. Maselli}a_,

E. Migliorea,b_{,V. Monaco}a,b_{,M. Musich}a_{,M.M. Obertino}a,c,2_{, G. Ortona}a,b_{,L. Pacher}a,b_{,N. Pastrone}a_,

M. Pelliccionia,G.L. Pinna Angionia,b_{, A. Potenza}a,b_{,A. Romero}a,b_{, M. Ruspa}a,c_{,R. Sacchi}a,b_,

A. Solanoa,b_{, A. Staiano}a_{, U. Tamponi}a

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

c_{UniversitàdelPiemonteOrientale(Novara),Torino,Italy}

S. Belfortea,V. Candelisea,b_{,M. Casarsa}a_{, F. Cossutti}a_{,G. Della Ricca}a,b_{, B. Gobbo}a_{, C. La Licata}a,b_,

M. Maronea,b_{,D. Montanino}a,b_{,A. Schizzi}a,b,2_{,T. Umer}a,b_{, A. Zanetti}a

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

S. Chang, A. Kropivnitskaya,S.K. Nam

KangwonNationalUniversity,Chunchon,RepublicofKorea

D.H. Kim,G.N. Kim, M.S. Kim,D.J. Kong, S. Lee, Y.D. Oh,H. Park, A. Sakharov, D.C. Son

KyungpookNationalUniversity,Daegu,RepublicofKorea

J.Y. Kim, S. Song

ChonnamNationalUniversity,InstituteforUniverseandElementaryParticles,Kwangju,RepublicofKorea

S. Choi, D. Gyun,B. Hong, M. Jo,H. Kim, Y. Kim,B. Lee, K.S. Lee, S.K. Park,Y. Roh

KoreaUniversity,Seoul,RepublicofKorea

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

UniversityofSeoul,Seoul,RepublicofKorea

Y. Choi,Y.K. Choi, J. Goh,E. Kwon, J. Lee, H. Seo,I. Yu

SungkyunkwanUniversity,Suwon,RepublicofKorea

A. Juodagalvis

VilniusUniversity,Vilnius,Lithuania

J.R. Komaragiri

NationalCentreforParticlePhysics,UniversitiMalaya,KualaLumpur,Malaysia

H. Castilla-Valdez, E. De La Cruz-Burelo,I. Heredia-de La Cruz30_{,R. Lopez-Fernandez,}

A. Sanchez-Hernandez

CentrodeInvestigacionydeEstudiosAvanzadosdelIPN,MexicoCity,Mexico

S. Carrillo Moreno, F. Vazquez Valencia

UniversidadIberoamericana,MexicoCity,Mexico

I. Pedraza, H.A. Salazar Ibarguen

BenemeritaUniversidadAutonomadePuebla,Puebla,Mexico

E. Casimiro Linares, A. Morelos Pineda

D. Krofcheck

UniversityofAuckland,Auckland,NewZealand

P.H. Butler,S. Reucroft

UniversityofCanterbury,Christchurch,NewZealand

A. Ahmad, M. Ahmad, Q. Hassan,H.R. Hoorani, S. Khalid, W.A. Khan, T. Khurshid,M.A. Shah, M. Shoaib

NationalCentreforPhysics,Quaid-I-AzamUniversity,Islamabad,Pakistan

H. Bialkowska,M. Bluj, B. Boimska,T. Frueboes, M. Górski, M. Kazana, K. Nawrocki,

K. Romanowska-Rybinska,M. Szleper, P. Zalewski

NationalCentreforNuclearResearch,Swierk,Poland

G. Brona,K. Bunkowski, M. Cwiok,W. Dominik,K. Doroba, A. Kalinowski,M. Konecki, J. Krolikowski,

M. Misiura, M. Olszewski, W. Wolszczak

InstituteofExperimentalPhysics,FacultyofPhysics,UniversityofWarsaw,Warsaw,Poland

P. Bargassa,C. Beirão Da Cruz E Silva, P. Faccioli, P.G. Ferreira Parracho,M. Gallinaro, F. Nguyen,

J. Rodrigues Antunes,J. Seixas, J. Varela, P. Vischia

LaboratóriodeInstrumentaçãoeFísicaExperimentaldePartículas,Lisboa,Portugal

I. Golutvin, V. Karjavin, V. Konoplyanikov,V. Korenkov, G. Kozlov,A. Lanev, A. Malakhov,V. Matveev31,

V.V. Mitsyn,P. Moisenz, V. Palichik,V. Perelygin, S. Shmatov, S. Shulha, N. Skatchkov,V. Smirnov,

E. Tikhonenko, A. Zarubin

JointInstituteforNuclearResearch,Dubna,Russia

V. Golovtsov,Y. Ivanov, V. Kim32,P. Levchenko, V. Murzin,V. Oreshkin, I. Smirnov, V. Sulimov,L. Uvarov,

S. Vavilov, A. Vorobyev,An. Vorobyev

PetersburgNuclearPhysicsInstitute,Gatchina(St.Petersburg),Russia

Yu. Andreev,A. Dermenev,S. Gninenko, N. Golubev, M. Kirsanov, N. Krasnikov, A. Pashenkov, D. Tlisov,

A. Toropin

InstituteforNuclearResearch,Moscow,Russia

V. Epshteyn,V. Gavrilov, N. Lychkovskaya,V. Popov, G. Safronov, S. Semenov, A. Spiridonov, V. Stolin,

E. Vlasov,A. Zhokin

InstituteforTheoreticalandExperimentalPhysics,Moscow,Russia

V. Andreev,M. Azarkin, I. Dremin, M. Kirakosyan, A. Leonidov, G. Mesyats,S.V. Rusakov, A. Vinogradov

P.N.LebedevPhysicalInstitute,Moscow,Russia

A. Belyaev,E. Boos,V. Bunichev, M. Dubinin7,L. Dudko, A. Ershov, V. Klyukhin, O. Kodolova, I. Lokhtin,

S. Obraztsov,S. Petrushanko,V. Savrin, A. Snigirev

SkobeltsynInstituteofNuclearPhysics,LomonosovMoscowStateUniversity,Moscow,Russia

I. Azhgirey,I. Bayshev,S. Bitioukov, V. Kachanov, A. Kalinin, D. Konstantinov,V. Krychkine, V. Petrov,

R. Ryutin, A. Sobol,L. Tourtchanovitch, S. Troshin, N. Tyurin, A. Uzunian,A. Volkov

StateResearchCenterofRussianFederation,InstituteforHighEnergyPhysics,Protvino,Russia

P. Adzic33_{,M. Dordevic, M. Ekmedzic, J. Milosevic}