Search for an L-mu - L-tau gauge boson using Z -gt; 4 mu events in proton-proton collisions at root s=13 TeV

SISTEMA DE BIBLIOTECAS DA UNICAMP

REPOSITÓRIO DA PRODUÇÃO CIENTIFICA E INTELECTUAL DA UNICAMP

Versão do arquivo anexado / Version of attached file:

Versão do Editor / Published Version

Mais informações no site da editora / Further information on publisher's website:

https://www.sciencedirect.com/science/article/pii/S037026931930214X

DOI: 10.1016/j.physletb.2019.01.072

Direitos autorais / Publisher's copyright statement:

©2019 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

Search

for

an

L

_μ

−

L

_τ

gauge

boson

using

Z

→

4

μ

events

in proton-proton

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:

Received10August2018

Receivedinrevisedform12December2018 Accepted8January2019

Availableonline28March2019 Editor:M.Doser Keywords: CMS Physics Zprime Muons

AsearchforanarrowZ gaugebosonwithamassbetween5and 70 GeVresultingfroman Lμ−Lτ

U(1)localgaugesymmetryisreported.Theoriesthatpredictsuchaparticlehavebeenproposedasan explanationofvariousexperimentaldiscrepancies,includingthelackofadark mattersignalin direct-detectionexperiments,tensioninthemeasurement oftheanomalousmagneticmomentofthemuon, andreportsofpossibleleptonflavoruniversalityviolationinB mesondecays.A datasampleof proton-protoncollisionsatacenter-of-massenergyof13 TeVisused,correspondingtoanintegratedluminosity of77.3 fb−1recordedin2016and2017bytheCMSdetectorattheLHC.Eventscontainingfourmuons withaninvariantmassnearthestandardmodelZ bosonmassareanalyzed,andtheselectionisfurther optimizedtobesensitivetotheeventsthatmaycontainZ_→Zμμ→4μdecays.Theeventyieldsare consistentwiththestandardmodelpredictions.Upperlimitsof10−8–10−7at95% confidencelevelare setontheproductofbranchingfractionsB(Z→Zμμ)B(Z→μμ),dependingontheZ mass,which excludesaZ bosoncouplingstrengthtomuonsabove0.004–0.3.Thesearethefirstdedicatedlimitson

Lμ−Lτ modelsattheLHCandresultinasignificantincreaseintheexcludedmodelparameterspace. TheresultsofthissearchmayalsobeusedtoconstrainthecouplingstrengthofanylightZgaugeboson tomuons.

©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Thestandardmodel(SM) ofparticlephysics [1–3] cannot ex-plainallexperimental observationstodateandis,therefore, gen-erallybelievedtobeanincompletetheory.EnlargingtheSMgauge group to include an additional U(1) symmetry is a simple and well-motivated extension [4–6], which leads to a predictionof a newvector particle, a Z boson.In order forthe extended gauge symmetryto be anomaly free,only certain generation-dependent couplingsareallowed.Theanomaly-freemodelweconsiderinthis paperistheLμ−Lτ gaugesymmetry [7],whereLμ andLτ arethe μand τ leptonnumbers,respectively.Theinteractionbetweenthe Z andthesecond- andthird-generationleptons canbe described withthefollowingLagrangian [8]:

LZ= −gZμ



L2γμL2+l2γμl2−L3γμL3−l3γμl3



, (1)

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

where g is an arbitrary dimensionless coupling to the SM left-handed and right-handed μ and τ multiplets. These multiplets are: L2=  νμ μ  L ,l2=μR, L3=  ντ τ  L and l3=τR. (2)

Additional U(1) gauge symmetries based on the difference in lepton family numbers are all anomaly free andrequire no new fermionic particle content.The model based ongauging Lμ−Lτ in particular is the least constrained experimentally, since it is coupledonlyto second- andthird-generationleptons. Thismodel hasgainedpopularityinrecentyears [9–15] asanexplanationfor severalanomalousexperimentalmeasurementsinparticlephysics. Theseanomaliesincludethemeasurementoftheanomalousmuon magnetic moment by the Muon g−2 Collaboration [16], which can be explainedfor certain values of the Z mass and coupling strength (g) [9,11]. In addition,if the Z mediates an interaction betweendarkmatterandordinarymatter,theboundsonthedark matter coupling strength from direct-detection experiments are lessstringent [12,13] sincetheparticularZ consideredheredoes https://doi.org/10.1016/j.physletb.2019.01.072

0370-2693/©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

Fig. 1. LeadingorderFeynmandiagramsforthesignalprocess(left)andthe dom-inantbackgroundprocess(right),whereineachdiagramthefour-muonfinalstate originatesfromannihilation.

Fig. 2. LeadingorderFeynmandiagramsforthesubdominantquark-initiated(left) andgluon-initiated(right)backgroundprocesses,whereineachdiagramthe four-muonfinalstateoriginatesfromconversion.

notcoupledirectlytoquarks.Finally,ifadditionalinteractions be-yond the minimal Lμ−Lτ model are assumed, abnormalities in kinematicangulardistributionsandleptonflavoruniversalitytests observedinB→K∗μ+μ−decays [17,18] canbeexplainedbythis model,givenitsflavornon-universalcouplings [10,13].

TheZgaugebosonassociatedwiththeputative Lμ−Lτ gauge symmetry can be sought at the CERN LHC. Since the Z couples only to second- and third-generation leptons (μ, νμ, τ and ντ ), it must be produced as a final state radiation product of a lep-tonoriginatingfromsomeother physicsprocess.The Z→4μ de-cay provides an extremelyclean source of muonswith excellent massresolution.Theresonant signaldecayZ→μμ thatmaybe present in Z→4μ decays further reduces the background con-tamination.Thereare two typesofirreduciblebackgroundwhere the additionaldimuon originatesfromannihilation orconversion topologies, as described in Ref. [19]. The Feynman diagrams in Fig.1(left)forthesignalandinFig.1(right)forthebackground are examplesof theannihilation topology,while thediagrams in Fig.2areexamplesoftheconversiontopology.Thedominant back-groundto thesearch comes fromresonant Z production and de-cay to 4μ fromthe annihilation diagram in Fig. 1 (right), while the continuum background originating from the conversion dia-gramsinFig.2aresubdominant.Inthediscussionoftheanalysis thatfollows,thesignalandbackgroundprocessesoriginatingfrom thediagramsofFig.1willhereafter be collectivelyreferred toas theZ→4μprocesssince theyhaveverysimilar kinematic prop-erties. The background processes originating from the diagrams in Fig. 1 (right) and Fig. 2 (left) will be collectively referred to as qq¯ →4μ, and the process originating from the diagram in Fig.2(right)willbereferredtoasgg→4μ.

The Z→4μ process hasbeenstudied bythe ATLAS andCMS Collaborations [20–22] and constraints on the Lμ−Lτ parame-ter space have been derived. However, these measurements are notoptimizedforthepresenceofa Z particle.Inparticular,they donot utilizethe factthat two ofthe fourmuonswouldforma resonant peak at the Z mass, providing a means to reduce the dominantbackgroundbyseveralordersofmagnitude.Thesubject

ofthispaperisadedicatedcountingexperimentsearchwitha fi-nalselectionbasedonthereconstructedZ candidatemass. 2. TheCMSdetector

AdetaileddescriptionoftheCMSdetector,togetherwitha def-inition of thecoordinatesystemused andtherelevant kinematic variables, can be found in Ref. [23]. The central feature of the CMS apparatusisa superconducting solenoidof6 minternal di-ameter, providing a magnetic field of 3.8 T.Within the solenoid volumeare asiliconpixelandstriptracker,aleadtungstate crys-talelectromagneticcalorimeter,andabrassandscintillatorhadron calorimeter, each composedof a barrelandtwo endcapsections. Forwardcalorimetersextendthepseudorapidity(η)coverage pro-videdby the barrelandendcapdetectors.Muonsare detected in gas-ionization chambers embedded in the steel flux-return yoke outsidethesolenoid.Thesilicontrackermeasureschargedparticles with|η|<2.5.Muonsaremeasured intheregion |η|<2.4,with detectionplanesmadeusingthreetechnologies:drifttubes, cath-odestripchambers,andresistiveplatechambers.Matchingmuons totracksmeasuredinthesilicontrackerresultsinarelative trans-verse momentum (pT) resolutionformuons with20 GeV<pT< 100 GeV of1.3–2.0% inthe barrel(|η|<0.9) andbetter than6% intheendcaps(|η|>0.9).Forchargedhadrons,primarilyusedfor the computationof muonisolation sumsinthissearch, thetrack resolutionsaretypically1.5%in pT and25–90(45–150) μminthe transverse(longitudinal)impactparameterfortransverse momen-tumbetween 1and10 GeV and|η|<1.4 [24].Thefirstlevelofthe CMS trigger system [25], composed of custom hardware proces-sors, uses informationfromthe calorimetersandmuon detectors toselectthemostinterestingeventsinafixedtimeintervalofless than 4 μs.Thehigh-leveltrigger(HLT)processorfarm further de-creases the event rate fromaround 100 kHz toless than 1 kHz beforedatastorage.

3. Dataandsimulatedsamples

This analysis makes use of proton-proton (pp) collision data recorded by the CMS detector in 2016 and 2017, corresponding to an integratedluminosity of 77.3 fb−1.Collisionevents are se-lected by HLT algorithms that require the presence of one, two, orthree muonspassing looseidentificationandisolation require-ments. The main triggers used for this analysis select a pair of muonswheretheminimalrequirementforthetransverse momen-tumwithrespecttothebeamaxisoftheleadingmuonis17 GeV, while that for the subleading muon is 8 GeV. To maximize the signal acceptance, triggers requiring three muonswith lower pT thresholds (12, 10and 5 GeV) andno isolation requirement are alsoused,asareisolatedsingle-muontriggerswiththethresholds of22 GeV and27 GeV for2016and2017datataking,respectively. Theoverall triggerefficiencyforsimulatedsignal eventsthatpass thefull selectionchainofthisanalysis(describedinSection 4) is greater than 99%.The triggerefficiencyis measured indatawith a method based on the “tag-and-probe” technique [26] using a sampleof4μeventscollectedbythesingle-muontriggers.Events withfourmuonshaveanegligiblecontamination from misidenti-fiedmuonsandthereforebackgroundsubtractionisnotnecessary. Muonsmatched tothesingle-muontriggersare usedastagsand the other threemuonsare used asprobes.The probe muonsare thenmatchedtothetriggeringmuonobjectsfromanyoftheone, two, orthree muon triggers, and the combined efficiency is ex-tracted. The efficiency in data is found to be in agreement with theexpectationfromsimulation.

Monte Carlo simulation samplesfor the Z signal andfor the background coming from the qq¯→4μ and gg→4μ processes

are used to optimizethe event selection, evaluate the signal ac-ceptance,andestimatethebackgroundrateandsystematic uncer-tainties.Thesignalisgeneratedatleading order(LO)in perturba-tivequantumchromodynamics(pQCD)with MadGraph5_amc@nlo (v2_4_2) [27] togetherwiththeUniversal FeynRules Output(UFO) modelfromRef. [8].Thesignal samplesaregeneratedwithm(Z)

rangingfrom5to70 GeV instepsof5 GeV.Form(Z)below5 GeV nonprompt muons become a challenging background, and for m(Z)above 70 GeV the Z boson startsto beproduced off mass-shell,requiringa dedicatedeventselection.The qq¯→4μprocess isgeneratedatnext-to-LO(NLO)inpQCDwith powheg2.0 [28–30], whilethegg→4μprocessisgeneratedatLOwith mcfm 7.0 [31]. The default set of parton distribution functions (PDFs) used in all simulations is NNPDF30_nlo_as_0118 [32]. The fully differen-tial cross section for the qq¯ →4μ process has been computed atnext-to-NLO (NNLO) [33], andthe appropriate NNLO/NLO cor-rection factor K of 1.03 at m(4μ)=m(Z) is used to correct the powheg sample. The qq¯ →4μ background production is domi-natedbytheconversiontopology atm(4μ)≈m(Z),andtherefore ananalogousNNLO/LO K factorof1.29 isusedtocorrectthe sig-nalprocessthat originatesfromthesametopology.Thegg→4μ processcontributesatNNLOinpQCD andiscorrectedbya K fac-torof2.4 [34–40].

Afterthe final selection, described in Section 5, the gg→4μ background contribution is typically less than 1% (and at most 7%) of the qq¯ →4μ contribution. These simulations have been foundtoprovide anaccurate descriptionof4μ eventsindataby severalprevious studies [22,41–43]. All the generated events are interfaced with pythia 8.212 [44] tune CUETP8M1 [45] to sim-ulatemultiple partoninteractions, the underlyingevent, andthe fragmentationandhadronizationeffects.Thegeneratedeventsare processedthroughadetailedsimulationoftheCMSdetectorbased on Geant4 [46,47] and reconstructed with the same algorithms thatare usedforthedata.The simulatedeventsinclude overlap-pingpp interactions(pileup)andhavebeenreweightedsothatthe distributionofthenumberofinteractionsperLHCbunchcrossing insimulationmatchesthatobservedindata.

4. Objectreconstruction

The techniques of the object reconstruction and event selec-tion are based largely on Refs. [22,41–43]. Event reconstruction is basedon the particle-flow (PF)algorithm [48], which exploits informationfromalltheCMSsubdetectors to identifyand recon-struct individual particles in the event. Higher-level observables, suchasmuonisolationquantities,arebuiltfromthePFcandidates classifiedaschargedhadrons,neutralhadrons,photons, electrons, ormuons.

Muons are reconstructed within the geometrical acceptance

|η|<2.4 by combininginformation from the silicon trackerand themuonsystem [49],andarerequiredtosatisfy pT>5 GeV.The innerandoutertracksarematchedusingeitheranoutside-in algo-rithm,startingfromatrackinthemuonsystem,oran inside-out algorithm,starting from a trackin thesilicon tracker.In the lat-tercase, some very low-pT muons that may not have sufficient energyto penetratetheentiremuonsystemarealsocollected by consideringtracks thatmatchtracksegments in onlyone ortwo planesofthemuonsystem. Muonsare identifiedfromthe recon-structedmuontrackcandidatesbyapplyingminimalrequirements ontheinner andouter tracks,takingintoaccounttheir compati-bilitywithsmallenergydepositsinthecalorimeters [48].

Muonsoriginatingfromnonpromptdecaysofhadronsare sup-pressed by requiringeach muon trackto havethe ratio between itsimpactparameterinthreedimensions, computedwithrespect to the chosen primary vertexposition, and its uncertainty to be

lessthan 4.Theprimary pp interaction vertexistakento be the reconstructedvertexwiththelargestvalue ofsummed p2_T ofjets andassociatedmissingtransversemomentum,calculatedfromthe tracks assigned to the vertex, where the jet finding algorithm is takenfromRefs. [50,51] andthemissingtransversemomentumis takenasthenegativevectorsumofthepT ofthejets.

ArelativeisolationrequirementofIμ<0.35 isimposedto dis-criminatebetweenpromptmuonsfromZ bosondecaysandthose arisingfromelectroweakdecaysofhadronswithinjets,wherethe relativeisolationisdefinedas

Iμ_≡

 

pcharged_T +max0,pneutral_T +pγ_T −pPU_T /pμ_T.

(3)

The isolation sumsinvolvedare all restrictedtoPF candidates within a volume bounded by a coneof angularradius R=0.3 around the muon direction at the primary vertex, where the angular distance between two particles i and j is R(i,j)= 

(ηi_−ηj₎2_{+ (φ}i_{− φ}j₎2 _{andφ istheazimuthal angleinradians.} The quantity pcharged_T is the scalar sum of the transverse mo-menta of charged hadrons originating from the chosen primary vertexoftheevent.Charged hadronsareassociatedwithcharged particle tracks assigned neither to electrons nor to muons. The quantities pneutral

T and

pγ_T are the scalarsums ofthe trans-versemomentaforneutralhadronsandphotons, respectively. En-ergydepositsfrompileupinteractions,pPU_T ,aresubtractedtomake theisolationvariablelesssensitivetothenumberofpileup inter-actions.Here,wedefine pPU_T ≡0.5_ipPU_T ,i,wherei runsoverthe momentaofthechargedhadronPFcandidatesnotoriginatingfrom theprimaryvertexandthefactorof0.5accountsforthedifferent fractionsofchargedandneutralparticlesinthecone.

An algorithmis usedto recover thefinal-stateradiation (FSR) photonsfrom muons. Photons reconstructed by the PFalgorithm within|ηγ|<2.4 arerequiredtosatisfy pγT >2 GeV andIγ<1.8. The photon relative isolation Iγ is defined asfor the muons in Eq. (3). Every FSR candidate is associated with the closest se-lectedmuonintheevent,andwerequireFSRcandidatestosatisfy

R(γ, μ)/(pγ_T)2<0.012 GeV−2 andR(γ, μ)<0.5.Finally, for every muon we retain theFSR candidate,ifany, withthelowest

R(γ, μ)/(pγ_T)2_{.About5%ofsignaleventsarefoundtohaveone} FSRphotonattached.AnyselectedFSRphotonsareexcludedfrom thecorrespondingmuonisolationcomputation.

Thedecayproducts ofknowndimuon resonances(J/ψ meson, Z boson)areusedtocalibratethemuonmomentumscaleand res-olutioninbinsofpT and η.Muonmomentaarecalibratedusinga Kalmanfilterapproach [52].A tag-and-probetechnique [26,53] is usedtomeasuretheefficiencyofthereconstructionandselection forpromptmuonsinseveralbinsofpT and η.Thedifference be-tweentheefficienciesmeasuredinsimulationanddata,whichon averageis1.2%permuon,isusedtocorrecttheselectionefficiency inthesimulatedsamples.Thecombinedmuonreconstructionand identification efficiency forsignal events, including these correc-tions,isabout92%permuon.

5. Eventselection

Events are required to contain at least four well-identified and isolated muons, with at least two muons required to have pT>10 GeV andatleast oneto have pT>20 GeV.The four se-lected muonsmust havezeronet charge. Dimuon candidatesare formedfrommuonpairsofoppositesign(μ+μ−)andarerequired to pass 4 GeV<_mμ+_μ− <120 GeV. All recovered FSR photon candidates are included in the invariant mass computation. The

dimuon candidates are then combined into Z→4μ candidates. WedefineZ₁tobethedimuoncandidatewiththehighest invari-antmass,andZ₂ astheotherone.Ineventswithmorethanfour muonswhereseveralZ→4μcandidateshavethesamem(Z₁),the Z₂ candidateformedfromthetwo muonswiththehighestscalar sumofpT ischosen.

Tobe considered forthe analysis, Z→4μ candidates haveto passasetofkinematicrequirements.TheZ₁ invariant massmust belargerthan12 GeV and allmuonsmustbe separatedin angu-larspacebyatleastR(μi, μj)>0.02.Tofurthersuppressevents

withmuons originatingfromhadron decays in jet fragmentation orfromthedecayoflow-masshadronicresonances,allfour oppo-sitesignmuonpairsthatcanbeconstructedwiththefourmuons are requiredto satisfy _mμ+_μ−>4 GeV, whereselected FSR pho-tons are disregarded in the invariant mass computation. Finally, the four-muon invariant mass m(4μ) must be between 80 and 100 GeV. The Z candidate is mostoftenreconstructed as Z₂ for m(Z)<42.65 GeV and as Z₁ form(Z)>42.65 GeV. The search is a counting experimentwith a sliding mass window, and a fi-nalselectionmadeoneitherm(Z₁)orm(Z₂)values,dependingon theZmasshypothesis.Theexclusionlimitform(Z)=42.65 GeV usingeitherm(Z₂)orm(Z₁)asan observable is aboutthe same. For m(Z)<42.65 GeV, m(Z₂) is required to be within 2% of the m(Z). While for m(Z)>42.65 GeV, the same requirement is applied on m(Z₁). The search window size of 2% was chosen to simultaneously optimize the expected significance and exclu-sionlimit for differentZ mass hypotheses.The efficiencyof this requirement is directly related to the efficiency of selecting the correct Z candidate and varies with Z mass. It is found to be about 63% form(Z)=5 GeV, 25% for m(Z)=40 GeV,and 67% form(Z)=70 GeV.Thelowefficiencyform(Z)≈mZ/2 isduethe combinatoricambiguityinselectingthecorrectZ candidatefrom thefourpossibledimuoncandidates.Theselectionis,however,still extremelybeneficial, asit eliminates approximately 99.8% ofthe SM γ∗/Z∗ backgroundform(Z)=40 GeV.Additionalbackgrounds tothe signal thatcan arise fromprocessesinwhich heavy-flavor jetsproduce secondary muons, and fromprocesses inwhich de-caysofheavy-flavorhadronsornonpromptdecaysoflightmesons within jetsare misidentified as prompt muons, are found to be negligibleafterthefinaleventselection.

6. Systematicuncertainties

Experimental uncertainties that equally affect the signal and backgroundestimations includethe uncertaintyin the integrated luminosity measurementof2.5% [54] and2.3% [55] for the2016 and2017datasets,respectively,andtheuncertaintyinthemuon reconstruction,identification,andisolationefficiency(4.9%onthe overall eventyield). An uncertaintyinthe signal andbackground yields due to the muon momentum scale is determined using Z→4μ events in data andsimulation and found to be negligi-ble(0.1%).An uncertaintyinthe signal andbackground yields of 2.0%comingfromthedeterminationofthemuonmomentum res-olution is obtained by smearing the dimuon mass resolution by 20% [43] withrespecttothenominalresolutionandrecomputing theexpectedyields.Theuncertaintiesduetothefinitesizesofthe simulatedsamplesamountto 3.0% forthe backgroundestimation and1.4%forthesignalestimation.

Theoretical uncertainties that affect both thesignal and back-groundestimationsincludeuncertaintiesinthefinite-order pertur-bativecalculationsandthechoiceofthePDFset.Theuncertainties arisingfromfinite-orderperturbativecalculationsareestimatedby varying the renormalizationand factorizationscales between 0.5 and2.0 times their nominalvalue, whilekeepingtheir ratios be-tween 0.5 and 2.0.Thisuncertainty isfoundto be3.5 (3.9)%for

the qq¯→4μ (gg→4μ) process and is taken to be correlated between thesignal andthe dominant qq¯→4μ background pro-cess.Theuncertaintyduetomissingelectroweakcorrectionsinthe regionm(4μ)≈m(Z)isexpectedtobesmallcomparedtothe un-certaintiesinthepQCDcalculation.FollowingRef. [34] andtaking into account differencesinselection,an additional uncertaintyof 10% inthe K factorusedforthegg→4μpredictiondescribedin Section 3isappliedto accountforthefactthat the K factorwas computed forthegg→H process.The uncertaintyfromthe PDF set is determined following the PDF4LHC recommendations [56] andisfoundtobe3.1 (3.5)%fortheqq¯→4μ(gg→4μ)process. Thisuncertaintyisalsotakentobe correlatedbetweenthesignal andthedominantqq¯→4μbackgroundprocess.

To estimate the effect of the interference between the signal and background processes, three types of samples are generated using MadGraph5_amc@nlo (v2_4_2):pp→4μ(inclusive),pp→ Zμμ →4μ(signalonly),andpp→4μ(backgroundonly).Inall g isvariedfrom0.01 to0.50,whichcorrespondstorelativewidths oflessthan2%inthemodelconsidered.Theinclusivesample con-tainsbackground,signal,andinterferencecontributions.Theeffect oftheinterferenceonthenormalizationofthesignalisestimated by takingthedifference oftheinclusivesample crosssectionand the sumofthecross sectionsofthesignal andbackground sam-ples.Thisdifferenceisatmost5.0%afterthefinaleventselection, andanadditional5.0%uncertaintyinthesignalyieldisappliedto accountforthiseffect.

The combinedsystematicuncertainties in thebackgroundand signalyieldsareabout8%and10%,respectively.

7. Results

The number ofcandidates observed indata andthe expected yields for the backgrounds and the different Z signals after the fulleventselectionarereportedinTable1.Thereconstructed four-muon invariant mass distributions are shownin Fig. 3and com-paredwiththeexpectationsfromsignalandbackgroundprocesses. Fig.4showsthereconstructedm(Z₁)andm(Z₂)distributions.

Inallcases,theobserveddistributions agreewiththe expecta-tionswithin theassigneduncertainties.Upperlimitsat95%

confi-Fig. 3. Distributionofthereconstructedfour-muoninvariantmassm4μinthefull massrangeandacomparisontothepredictedqq¯/gg→4μbackground.Theblue histogram representsthe expectedSM 4μbackgrounddistributionand thegray bandshowsthesystematicuncertaintyinitsprediction.Forillustration,threeZ signalhypotheseswithdifferentmassesandcouplingstrengthsareshownby col-oredlines.

Table 1

Thenumbersofexpectedbackgroundandsignaleventsandthenumbersofobservedcandidateeventsafterthefullselectionwith 80 GeV<m4μ<100 GeV.Thesignalandqq¯/gg→4μbackgroundratesarebothestimatedfromsimulation.Thesignalpredictionsare reportedwithsystematicuncertaintiesonly,whilethebackgroundpredictionsarereportedwithstatisticalandsystematicuncertainties, respectively.Alsoshownarethenumbersofexpectedbackgroundandsignaleventsandthenumbersofobservedcandidateeventsin therelevantmasswindowsforthreem(Z)hypotheses.Thevaluesofthecouplingstrengthsarechosenforthepurposeofillustration.

Background m(Z)=5 GeV g=0.008 m(Z)=15 GeV g=0.01 m(Z)=70 GeV g=0.5 Observed data 80 GeV<m4μ<100 GeV 423.0±20.6±33.4 37.1±3.7 31.4±3.1 53.8±5.4 441 4.9 GeV<m(Z₂) <5.1 GeV 9.2±3.0±0.7 23.3±2.3 — — 13 14.7 GeV<m(Z2) <15.3 GeV 7.7±2.8±0.6 — 18.9±1.9 — 6 68.6 GeV<m(Z1) <71.4 GeV 34.9±5.9±2.8 — — 36.0±3.6 35 Predictedσ× B[fb] — 9.6 3.0 12 —

Fig. 4. Distributionsofthereconstructedm(Z1)andm(Z2)observablesandacomparisontothepredictedqq¯/gg→4μbackground.Thevariablebinwidthhasbeenchosen

accordingtotheexpectedmassresolution.ThebluehistogramrepresentstheexpectedSM 4μbackgrounddistributionsandthegraybandshowsthesystematicuncertainty initsprediction.Forillustration,threeZsignalhypotheseswithdifferentmassesandcouplingstrengthsarealsoshownbycoloredlines.

dencelevel(CL)arederivedontheproductoftheZμμproduction cross section and the branching fraction B(Z→μμ) using the CLs method [57,58] with the test statistic described in Ref. [59], inthe asymptoticapproximation [60].Theasymptotic approxima-tionwasverifiedtobevalidbycomputinglimitswiththefullCLs method using pseudo-experiments for several m(Z) hypotheses. A linear interpolationof theexpected eventyields between gen-eratedsignal simulationsamples isassumedin thelimit calcula-tions.Systematicuncertaintiesareincorporatedintothelikelihood asnuisanceparameters withlog-normal probability distributions. Dueto thelow numberof eventspassing thefinal selection, the statisticaluncertaintyisalways largerthan 22%within theentire m(Z)searchregion,anddominatesthesensitivityofthisanalysis. TheselimitsareshowninFig. 5.Theupperlimitson theB(Z→ Zμμ)B(Z→μμ) are alsoshown. Forthe derivation of branch-ingfractionlimits,theZ bosonproductioncrosssectionprediction computedatNNLOin pQCDwiththe programFEWZ 2.1 [61–63] isused.

Upperlimitsarealsoderivedonthegaugecouplingstrength g andcompared toother experimentalconstraints,showninFig.6. These limits assume the B(Z→μμ) is equal to 1/3 as in the minimal Lμ−Lτ model with equal left- and right-handed cou-pling strengths, andthe additional constraints are adapted from Ref. [13]. The mass of the dark matter candidate in the model fromRef. [13] is assumedto be much larger than the largest Z massconsideredandthegaugecouplingstrengths toother parti-cles,suchasb- ands-quarks, aretakento bemuch smallerthan

thecoupling strengthto leptons sothat B(Z→μμ)is constant. The natural widthof the Z isalso assumed to be less than the detector resolution, which is a valid approximation in the mini-malLμ−Lτ modelwhen g2_{/4π<0.01.Theshadedyellowregion} showsconstraintsderivedinRef. [13] fromtheATLASB(Z→4μ)

measurement at √s=7 and 8 TeV [21]. The shaded red region isexcluded bythemeasurement oftheso-calledneutrinotrident crosssection by theCCFRCollaboration [64,65]. Thegreen region is excluded bya globalanalysis ofBs mixingmeasurements per-formed inRef. [13].The regionin betweenthose two constraints andform(Z)>10 GeV isacandidateregiontoexplain theLHCb Bdecayanomalies [17,18].Itisimportanttonotethatinorderto explain theseanomalies,additionalassumptions onthecouplings oftheZbosontob- ands-quarksarerequired,andtheconstraints fromBsmixingmeasurementsarethereforenotgenerally applica-bletotheminimal Lμ−Lτ model.Itcanbeseenthatthissearch is ableto exclude a significant portion ofthe previously allowed parameterspace.

8. Summary

Asearch fora Zgauge bosonresultingfroman Lμ−Lτ U(1)

local gauge symmetry is presented, based on data from proton-proton collisions at √s=13 TeV correspondingto an integrated luminosity of 77.3 fb−1 recorded in 2016 and2017 by the CMS detector at the LHC. Events with four muons having an invari-ant mass near the mass of the standard model Z boson are

se-Fig. 5. Expectedandobserved95%CL limitsontheproductoftheZμμ produc-tioncrosssectionandbranchingfraction(lefty-axis)andB(Z→Zμμ)B(Z→μμ)

(righty-axis).Thedashedblackcurveistheexpectedupperlimit,withoneand twostandard-deviationbandsshowningreenand yellow,respectively. Thesolid blackcurveistheobservedupperlimit.Thecoloredlinesshowthepredictedcross sectiontimesbranchingfraction(lefty-axis)andB(Z→Zμμ)B(Z→μμ)(right y-axis)asafunctionofm(Z)forthreedifferentcouplingstrengths,chosenfor il-lustration.TheB(Z→μμ)istakentobe1/3 toderivethetheoreticalpredictions. lected,andthesearch sensitivityisoptimized forthepresence of Z→Zμμ→4μ decays.The search places strong constraintson theories that attempt to explain various experimental anomalies includingthe lackof a darkmatter signal in direct-detection ex-periments,tensioninthemeasurementoftheanomalousmagnetic momentofthemuon,andreportsofpossibleleptonflavor univer-salityviolationinB mesondecays.Theeventyieldsareconsistent withthestandardmodelexpectations.Upperlimitsof10−8_–10−7 at95% confidencelevelare setonthe productofbranching frac-tionsB(Z→Zμμ)B(Z→μμ),dependingontheZmass,which excludesaZ bosoncouplingstrength tomuonsabove0.004–0.3. ThesearethefirstdedicatedlimitsonLμ−Lτ modelsattheLHC andresultinasignificantincreaseintheexcludedmodel parame-terspace.

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,wegratefullyacknowledgethecomputingcentersand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythe computinginfrastructureessential to ouranalyses. Finally, we acknowledge the enduring support for the construc-tionandoperation oftheLHCandthe CMSdetectorprovidedby thefollowingfundingagencies:BMWFWandFWF(Austria);FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIEN-CIAS(Colombia);MSESandCSF(Croatia);RPF(Cyprus);SENESCYT (Ecuador); MoER, ERC IUT, and ERDF (Estonia); Academy of Fin-land,MEC,andHIP(Finland);CEAandCNRS/IN2P3(France);BMBF, DFG, andHGF (Germany); GSRT (Greece);NKFIA (Hungary); DAE andDST (India);IPM (Iran);SFI (Ireland);INFN (Italy); MSIP and NRF(RepublicofKorea);LAS(Lithuania);MOEandUM(Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT(Portugal);JINR(Dubna);MON,ROSATOM,RASandRFBR (Rus-sia);MESTD(Serbia); SEIDI,CPAN,PCTIandFEDER(Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST,

Fig. 6. Top:Expectedandobserved95%CL limitsonthegaugecouplingstrengthg

asafunctionofm(Z).Thedashedblackcurveistheexpectedupperlimit,with one and twostandard-deviationbandsshown ingreenandyellow, respectively. Thesolidblackcurveistheobservedupperlimit.TheB(Z→μμ)=1/3 isused toderivetheupperlimits.Thehatchedareashowstheregionwherethenarrow width approximationisno longervalid.Bottom:comparisonwith other experi-mentssensitivetothesameparameterspace,withshadedregionsbeingexcluded asdescribedinthetext.ThesethreeconstraintsareadaptedfromRef. [13]. STAR, andNSTDA (Thailand); TUBITAK andTAEK (Turkey); NASU andSFFR(Ukraine);STFC(UnitedKingdom);DOEandNSF(USA).

Individuals have received support from the Marie-Curie pro-gramandtheEuropeanResearchCouncilandHorizon2020Grant, contract No. 675440 (European Union); the Leventis Founda-tion; the Alfred P. Sloan Foundation; the Alexander von Hum-boldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voorInnovatie door Wetenschap en Technologie (IWT-Belgium); the F.R.S.-FNRS and FWO (Belgium) under the “Excellence of Science - EOS” - be.h project n. 30820817; the Ministry of Education, Youth and Sports (MEYS) of the Czech Republic; the Lendület (“Mo-mentum”) Program and the János Bolyai Research Scholarship of the Hungarian Academy of Sciences, the New National Excel-lence Program ÚNKP,the NKFIAresearch grants 123842, 123959, 124845, 124850 and 125105 (Hungary); the Council of Science and Industrial Research, India; the HOMING PLUS program of

the Foundation for Polish Science, cofinanced from European Union,Regional DevelopmentFund, theMobilityPlus programof the Ministry of Science and Higher Education, the National Sci-ence Center (Poland), contracts Harmonia 2014/14/M/ST2/00428, Opus2014/13/B/ST2/02543,2014/15/B/ST2/03998,and2015/19/B/ ST2/02861,Sonata-bis2012/07/E/ST2/01406;theNationalPriorities ResearchProgrambyQatarNationalResearchFund;thePrograma Estatal de Fomento de la Investigación Científica y Técnica de ExcelenciaMaríade Maeztu,grantMDM-2015-0509 andthe Pro-grama Severo Ochoa del Principado de Asturias; the Thalis and Aristeiaprograms cofinancedbyEU-ESF andtheGreek NSRF;the Rachadapisek Sompot Fund for Postdoctoral Fellowship, Chula-longkornUniversity andthe ChulalongkornAcademicintoIts 2nd CenturyProjectAdvancementProject (Thailand);theWelch Foun-dation,contractC-1845;andtheWestonHavensFoundation(USA). References

[1] S.L.Glashow,Partial-symmetriesofweakinteractions,Nucl. Phys.22(1961) 579,https://doi.org/10.1016/0029-5582(61)90469-2.

[2] S.Weinberg,Amodelofleptons,Phys.Rev.Lett.19(1967)1264,https://doi. org/10.1103/PhysRevLett.19.1264.

[3]A.Salam,Weakandelectromagneticinteractions,in:N. Svartholm(Ed.), El-ementaryParticlePhysics:RelativisticGroupsandAnalyticity,Proceedingsof theEighthNobelSymposium,Almquvist&Wiskell,1968,p. 367.

[4] P.Langacker,ThephysicsofheavyZgaugebosons,Rev.Mod.Phys.81(2009) 1199,https://doi.org/10.1103/RevModPhys.81.1199,arXiv:0801.1345. [5] A. Leike, The phenomenology of extra neutral gauge bosons, Phys. Rep.

317 (1999) 143, https://doi.org/10.1016/S0370-1573(98)00133-1, arXiv:hep -ph/9805494.

[6] J. Hewett, T. Rizzo, Low-energy phenomenology of superstring-inspired E6 models, Phys. Rep. 183 (1989) 193, https://doi.org/10.1016/0370-1573(89) 90071-9.

[7] X.-G.He,G.C.Joshi,H.Lew,R.R.Volkas,Simplest Z model,Phys.Rev.D44 (1991)2118,https://doi.org/10.1103/PhysRevD.44.2118.

[8] F. del Aguila, M. Chala, J. Santiago, Y. Yamamoto, Collider limits on lep-tophilicinteractions,J. HighEnergyPhys.03(2015)59,https://doi.org/10.1007/ JHEP03(2015)059,arXiv:1411.7394.

[9] S.Baek, N.G.Deshpande, X.-G.He, P.Ko,Muonanomalousg-2and gauged

Lμ−Lτ models, Phys. Rev. D 64 (2001) 055006, https://doi.org/10.1103/ PhysRevD.64.055006,arXiv:hep-ph/0104141.

[10] W. Altmannshofer, S. Gori, M. Pospelov, I. Yavin, Quark flavor transitions inLμ−Lτ models,Phys.Rev.D89(2014)095033, https://doi.org/10.1103/ PhysRevD.89.095033,arXiv:1403.1269.

[11] K.Harigaya,T.Igari,M.M.Nojiri,M.Takeuchi,K.Tobe,Muong-2andLHC phe-nomenologyintheLμ- Lτ gaugesymmetricmodel,J. HighEnergyPhys.03 (2014)105,https://doi.org/10.1007/JHEP03(2014)105,arXiv:1311.0870. [12] N.F.Bell,Y.Cai,R.K.Leane,A.D.Medina,Leptophilicdarkmatterwith Z

in-teractions,Phys.Rev.D90(2014)035027,https://doi.org/10.1103/PhysRevD.90. 035027,arXiv:1407.3001.

[13] W.Altmannshofer,S.Gori,S.Profumo,F.S.Queiroz,Explainingdarkmatterand BdecayanomalieswithanLμ–Lτ model,J. HighEnergyPhys.12(2016)106, https://doi.org/10.1007/JHEP12(2016)106,arXiv:1609.04026.

[14] F.Elahi,A.Martin,ConstraintsonLμ−LτinteractionsattheLHCandbeyond, Phys. Rev.D93 (2016)015022, https://doi.org/10.1103/PhysRevD.93.015022, arXiv:1511.04107.

[15] F.Elahi,A.Martin,Usingthe modifiedmatrixelementmethod toconstrain

Lμ−Lτ interactions,Phys.Rev.D96(2017)015021,https://doi.org/10.1103/ PhysRevD.96.015021,arXiv:1705.02563.

[16] G.W.Bennett,etal.,Muong-2,FinalreportoftheE821muonanomalous mag-neticmomentmeasurementatBNL,Phys.Rev.D73(2006)072003,https:// doi.org/10.1103/PhysRevD.73.072003,arXiv:hep-ex/0602035.

[17] LHCbCollaboration, Measurementofform-factor-independentobservablesin thedecayB0_→K∗0_μ+_μ−_{,Phys.Rev.Lett.111(2013)191801,https://doi.org/} 10.1103/PhysRevLett.111.191801,arXiv:1308.1707.

[18] LHCbCollaboration,TestofleptonuniversalityusingB+→K++− decays, Phys. Rev. Lett. 113(2014) 151601, https://doi.org/10.1103/PhysRevLett.113. 151601,arXiv:1406.6482.

[19] F.A.Berends, R.Pittau, R.Kleiss, Allelectroweak four fermionprocesses in electron-positron collisions,Nucl.Phys.B424(1994)308,https://doi.org/10. 1016/0550-3213(94)90297-6,arXiv:hep-ph/9404313.

[20] CMSCollaboration,ObservationofZdecaystofourleptonswiththeCMS de-tectorattheLHC,J. HighEnergyPhys.12(2012)034,https://doi.org/10.1007/ JHEP12(2012)034,arXiv:1210.3844.

[21] ATLASCollaboration, Measurementsof four-leptonproductionat the Z res-onance inpp collisionsat √s=7 and8 TeVwith ATLAS, Phys. Rev.Lett. 112 (2014) 231806, https://doi.org/10.1103/PhysRevLett.112.231806, arXiv: 1403.5657.

[22] CMSCollaboration,Measurementsofthepp→ZZproductioncrosssectionand theZ→4branchingfraction,andconstraintsonanomaloustriplegauge cou-plingsat√s=13 TeV,Eur.Phys.J.C78(2018)165,https://doi.org/10.1140/ epjc/s10052-018-5567-9,arXiv:1709.08601.

[23] CMSCollaboration,TheCMSexperimentattheCERNLHC,J. Instrum.3(2008) S08004,https://doi.org/10.1088/1748-0221/3/08/S08004.

[24] CMSCollaboration,Descriptionandperformanceoftrackandprimary-vertex reconstructionwiththeCMStracker,J. Instrum.9(2014)P10009,https://doi. org/10.1088/1748-0221/9/10/P10009,arXiv:1405.6569.

[25] CMS Collaboration, The CMStrigger system, J. Instrum. 12 (2017) P01020, https://doi.org/10.1088/1748-0221/12/01/P01020,arXiv:1609.02366. [26] CMSCollaboration,MeasurementoftheinclusiveWandZproductioncross

sectionsinppcollisionsat√s=7 TeV,J. HighEnergy Phys.10(2011)132, https://doi.org/10.1007/JHEP10(2011)132,arXiv:1107.4789.

[27] J.Alwall,R.Frederix,S.Frixione,V.Hirschi,F.Maltoni,O.Mattelaer,H.-S.Shao, T.Stelzer,P.Torrielli,M.Zaro,Theautomatedcomputationoftree-leveland next-to-leadingorderdifferentialcrosssections,andtheirmatchingtoparton showersimulations,J. HighEnergyPhys.07(2014)79,https://doi.org/10.1007/ JHEP07(2014)079,arXiv:1405.0301.

[28] P.Nason,AnewmethodforcombiningNLOQCD withshowerMonteCarlo algorithms,J. HighEnergyPhys.11(2004)040,https://doi.org/10.1088/1126 -6708/2004/11/040,arXiv:hep-ph/0409146.

[29] S.Frixione,P.Nason,C.Oleari,MatchingNLOQCDcomputationswithparton showersimulations:thePOWHEGmethod,J. HighEnergyPhys.11(2007)070, https://doi.org/10.1088/1126-6708/2007/11/070,arXiv:0709.2092.

[30] S.Alioli, P. Nason, C.Oleari,E. Re,A general framework for implementing NLOcalculationsinshowerMonteCarloprograms:thePOWHEGBOX,J. High Energy Phys. 06(2010)043,https://doi.org/10.1007/JHEP06(2010)043,arXiv: 1002.2581.

[31] J.M.Campbell,R.K.Ellis,MCFMforthe TevatronandtheLHC,Nucl.Phys.B, Proc.Suppl.205–206(2010)10,https://doi.org/10.1016/j.nuclphysbps.2010.08. 011,arXiv:1007.3492.

[32] R.D.Ball,V.Bertone,F.Cerutti,L.DelDebbio,S.Forte,A.Guffanti,J.I.Latorre, J.Rojo,M.Ubiali,Unbiasedglobaldeterminationofpartondistributionsand theiruncertaintiesatNNLOandatLO,Nucl.Phys.B855(2012)153,https:// doi.org/10.1016/j.nuclphysb.2011.09.024,arXiv:1107.2652.

[33] M.Grazzini,S.Kallweit,D.Rathlev,ZZproductionat theLHC:fiducialcross sectionsanddistributionsinNNLOQCD,Phys.Lett.B750(2015)407,https:// doi.org/10.1016/j.physletb.2015.09.055,arXiv:1507.06257.

[34] M.Bonvini,F.Caola,S.Forte,K.Melnikov,G.Ridolfi,Signal-background interfer-enceeffectsingg→H→W W beyondleadingorder,Phys.Rev.D88(2013) 034032,https://doi.org/10.1103/PhysRevD.88.034032,arXiv:1304.3053. [35] K.Melnikov,M.Dowling,ProductionoftwoZ-bosonsingluonfusioninthe

heavytopquarkapproximation,Phys.Lett.B744(2015)43,https://doi.org/10. 1016/j.physletb.2015.03.030,arXiv:1503.01274.

[36] C.S. Li,H.T. Li,D.Y. Shao, J. Wang,Soft gluonresummation in the signal-backgroundinterferenceprocessofgg(→h∗)→Z Z ,J. HighEnergyPhys.08 (2015)065,https://doi.org/10.1007/JHEP08(2015)065,arXiv:1504.02388. [37] G.Passarino,HiggsCAT,Eur.Phys.J.C74(2014)2866,https://doi.org/10.1140/

epjc/s10052-014-2866-7,arXiv:1312.2397.

[38] S.Catani,M.Grazzini,Next-to-next-to-leading-ordersubtractionformalismin hadron collisionsanditsapplicationtoHiggs-bosonproductionattheLarge Hadron Collider, Phys. Rev.Lett. 98(2007) 222002, https://doi.org/10.1103/ PhysRevLett.98.222002,arXiv:hep-ph/0703012.

[39] M.Grazzini,NNLOpredictionsfortheHiggsbosonsignalintheH→WW→

ννandH→ZZ→4decaychannels,J. HighEnergyPhys.02(2008)043, https://doi.org/10.1088/1126-6708/2008/02/043,arXiv:0801.3232.

[40] M.Grazzini,H.Sargsyan, Heavy-quarkmass effectsinHiggsboson produc-tionattheLHC,J. HighEnergyPhys.09(2013)129,https://doi.org/10.1007/ JHEP09(2013)129,arXiv:1306.4581.

[41] CMSCollaboration, Measurementoftheproperties ofaHiggsboson inthe four-leptonfinalstate,Phys.Rev.D89(2014)092007,https://doi.org/10.1103/ PhysRevD.89.092007,arXiv:1312.5353.

[42] CMSCollaboration,Measurementofdifferentialandintegratedfiducialcross sectionsforHiggsbosonproduction inthefour-leptondecaychannelinpp collisionsat √s=7 and8 TeV,J. HighEnergyPhys.04(2016)005,https:// doi.org/10.1007/JHEP04(2016)005,arXiv:1512.08377.

[43] CMS Collaboration, Measurements ofproperties ofthe Higgs boson decay-inginto thefour-leptonfinalstate inpp collisionsat √s=13 TeV,J. High Energy Phys. 11(2017) 047,https://doi.org/10.1007/JHEP11(2017)047,arXiv: 1706.09936.

[44] T.Sjöstrand, S.Ask,J.R. Christiansen,R.Corke, N.Desai,P.Ilten,S.Mrenna, S.Prestel,C.O.Rasmussen,P.Z.Skands,AnintroductiontoPYTHIA 8.2, Com-put.Phys.Commun.191(2015)159,https://doi.org/10.1016/j.cpc.2015.01.024, arXiv:1410.3012.

[45] CMSCollaboration,Eventgeneratortunesobtainedfromunderlyingeventand multipartonscatteringmeasurements,Eur.Phys.J.C76(2016)155,https:// doi.org/10.1140/epjc/s10052-016-3988-x,arXiv:1512.00815.

[46] S. Agostinelli, et al., GEANT4, Geant4—A simulation toolkit, Nucl. Instrum. MethodsA506(2003)250,https://doi.org/10.1016/S0168-9002(03)01368-8. [47] J.Allison,etal., Geant4 developmentsandapplications,IEEETrans.Nucl.Sci.

53(2006)270,https://doi.org/10.1109/TNS.2006.869826.

[48] CMSCollaboration, Particle-flowreconstructionand globaleventdescription withtheCMSdetector,J. Instrum.12(2017)P10003,https://doi.org/10.1088/ 1748-0221/12/10/P10003,arXiv:1706.04965.

[49] CMSCollaboration,PerformanceoftheCMSmuondetectorandmuon recon-structionwithproton-protoncollisionsat√s=13 TeV,J. Instrum.13(2018) P06015,https://doi.org/10.1088/1748-0221/13/06/P06015,arXiv:1804.04528. [50] M.Cacciari,G.P.Salam,G.Soyez,Theanti-kT jetclusteringalgorithm,J. High

Energy Phys. 04(2008)063,https://doi.org/10.1088/1126-6708/2008/04/063, arXiv:0802.1189.

[51] M.Cacciari,G.P.Salam,G.Soyez,FastJetusermanual,Eur.Phys.J.C72(2012) 1896,https://doi.org/10.1140/epjc/s10052-012-1896-2,arXiv:1111.6097. [52] R.Frühwirth,ApplicationofKalmanfilteringtotrackandvertexfitting,Nucl.

Instrum. Methods A 262(1987) 444, https://doi.org/10.1016/0168-9002(87) 90887-4.

[53] CMSCollaboration,PerformanceofCMSmuonreconstructioninppcollision eventsat √s=7 TeV,J. Instrum.7(2012)P10002, https://doi.org/10.1088/ 1748-0221/7/10/P10002,arXiv:1206.4071.

[54] CMSCollaboration,CMSluminosity measurementsforthe 2016datataking period,CMSPhysicsAnalysisSummaryCMS-PAS-LUM-17-001,URL:https://cds. cern.ch/record/2257069,2017.

[55] CMSCollaboration,CMSluminositymeasurementforthe2017data-taking pe-riodat√s=13 TeV,CMSPhysicsAnalysisSummaryCMS-PAS-LUM-17-004, URL:http://cdsweb.cern.ch/record/2621960,2017.

[56] J.Butterworth, etal., PDF4LHCrecommendationsfor LHCRun II,J. Phys.G 43(2016)023001,https://doi.org/10.1088/0954-3899/43/2/023001,arXiv:1510. 03865.

[57] T.Junk,Confidencelevelcomputationforcombiningsearcheswithsmall statis-tics,Nucl.Instrum.MethodsA434(1999)435,https://doi.org/10.1016/S0168 -9002(99)00498-2,arXiv:hep-ex/9902006.

[58] A.L.Read,Presentationofsearchresults:theCLstechnique,J. Phys.G28(2002)

2693,https://doi.org/10.1088/0954-3899/28/10/313.

[59] ATLAS,CMS,LHCHiggsCombinationGroup,ProcedurefortheLHCHiggsBoson SearchCombinationinSummer2011,TechnicalReportCMS-NOTE-2011-005. ATL-PHYS-PUB-2011-11,2011,URL:https://cds.cern.ch/record/1379837. [60] G.Cowan,K.Cranmer,E.Gross,O.Vitells,Asymptoticformulaefor

likelihood-basedtestsofnewphysics,Eur.Phys.J.C71(2011)1554,https://doi.org/10. 1140/epjc/s10052-011-1554-0, arXiv:1007.1727, Erratum: https://doi.org/10. 1140/epjc/s10052-013-2501-z.

[61] K.Melnikov,F.Petriello,TheW bosonproductioncross sectionat theLHC through O(α2

s), Phys. Rev. Lett. 96 (2006) 231803, https://doi.org/10.1103/

PhysRevLett.96.231803,arXiv:hep-ph/0603182.

[62] R.Gavin, Y. Li,F.Petriello, S.Quackenbush, FEWZ 2.0:a codefor hadronic Z productionat next-to-next-to-leadingorder, Comput. Phys.Commun.182 (2011)2388,https://doi.org/10.1016/j.cpc.2011.06.008,arXiv:1011.3540. [63] R. Gavin, Y. Li, F. Petriello, S. Quackenbush, W physics at the LHC with

FEWZ 2.1,Comput.Phys.Commun.184(2013)208,https://doi.org/10.1016/j. cpc.2012.09.005,arXiv:1201.5896.

[64] S.R.Mishra,etal.,CCFR,NeutrinotridentsandW-Zinterference,Phys.Rev.Lett. 66(1991)3117,https://doi.org/10.1103/PhysRevLett.66.3117.

[65] W. Altmannshofer, S. Gori, M. Pospelov, I. Yavin, Neutrino trident pro-duction: a powerful probe of new physics with neutrino beams, Phys. Rev.Lett.113(2014)091801,https://doi.org/10.1103/PhysRevLett.113.091801, arXiv:1406.2332.

TheCMSCollaboration

A.M. Sirunyan,A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam, F. Ambrogi, E. Asilar,T. Bergauer, J. Brandstetter, M. Dragicevic,J. Erö,A. Escalante Del Valle,

M. Flechl,R. Frühwirth1, V.M. Ghete, J. Hrubec, M. Jeitler1, N. Krammer,I. Krätschmer,D. Liko,

T. Madlener, I. Mikulec,N. Rad, H. Rohringer, J. Schieck1,R. Schöfbeck, M. Spanring, D. Spitzbart,

A. Taurok,W. Waltenberger, J. Wittmann, C.-E. Wulz1, M. Zarucki

InstitutfürHochenergiephysik,Wien,Austria

V. Chekhovsky, V. Mossolov,J. Suarez Gonzalez

InstituteforNuclearProblems,Minsk,Belarus

E.A. De Wolf,D. Di Croce, X. Janssen, J. Lauwers,M. Pieters,H. Van Haevermaet, P. Van Mechelen,

N. Van Remortel

UniversiteitAntwerpen,Antwerpen,Belgium

S. Abu Zeid,F. Blekman, J. D’Hondt, I. De Bruyn, J. De Clercq, K. Deroover, G. Flouris, D. Lontkovskyi,

S. Lowette,I. Marchesini, S. Moortgat, L. Moreels,Q. Python, K. Skovpen, S. Tavernier, W. Van Doninck,

P. Van Mulders, I. Van Parijs

VrijeUniversiteitBrussel,Brussel,Belgium

D. Beghin,B. Bilin, H. Brun, B. Clerbaux, G. De Lentdecker, H. Delannoy, B. Dorney,G. Fasanella, L. Favart,

R. Goldouzian, A. Grebenyuk,A.K. Kalsi, T. Lenzi,J. Luetic, N. Postiau,E. Starling, L. Thomas,

C. Vander Velde, P. Vanlaer, D. Vannerom,Q. Wang

T. Cornelis,D. Dobur, A. Fagot,M. Gul, I. Khvastunov2,D. Poyraz, C. Roskas, D. Trocino, M. Tytgat,

W. Verbeke,B. Vermassen, M. Vit, N. Zaganidis

GhentUniversity,Ghent,Belgium

H. Bakhshiansohi,O. Bondu, S. Brochet,G. Bruno, C. Caputo, P. David,C. Delaere, M. Delcourt,

A. Giammanco,G. Krintiras, V. Lemaitre,A. Magitteri, A. Mertens, M. Musich, K. Piotrzkowski,A. Saggio,

M. Vidal Marono, S. Wertz,J. Zobec

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

F.L. Alves,G.A. Alves,M. Correa Martins Junior, G. Correia Silva,C. Hensel, A. Moraes,M.E. Pol,

P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas, W. Carvalho,J. Chinellato3, E. Coelho, E.M. Da Costa, G.G. Da Silveira4,

D. De Jesus Damiao,C. De Oliveira Martins, S. Fonseca De Souza, H. Malbouisson, D. Matos Figueiredo,

M. Melo De Almeida,C. Mora Herrera,L. Mundim, H. Nogima,W.L. Prado Da Silva, L.J. Sanchez Rosas,

A. Santoro,A. Sznajder, M. Thiel, E.J. Tonelli Manganote3,F. Torres Da Silva De Araujo,

A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahujaa,C.A. Bernardesa, L. Calligarisa,T.R. Fernandez Perez Tomeia,E.M. Gregoresb,

P.G. Mercadanteb,S.F. Novaesa,Sandra S. Padulaa

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

A. Aleksandrov, R. Hadjiiska,P. Iaydjiev, A. Marinov, M. Misheva, M. Rodozov,M. Shopova, G. Sultanov

InstituteforNuclearResearchandNuclearEnergy,BulgarianAcademyofSciences,Sofia,Bulgaria

A. Dimitrov,L. Litov, B. Pavlov,P. Petkov

UniversityofSofia,Sofia,Bulgaria

W. Fang5, X. Gao5,L. Yuan

BeihangUniversity,Beijing,China

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

F. Romeo,S.M. Shaheen6,A. Spiezia, J. Tao, Z. Wang, E. Yazgan, H. Zhang,S. Zhang6,J. Zhao

InstituteofHighEnergyPhysics,Beijing,China

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

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

Y. Wang

TsinghuaUniversity,Beijing,China

C. Avila,A. Cabrera, C.A. Carrillo Montoya, L.F. Chaparro Sierra, C. Florez,C.F. González Hernández,

M.A. Segura Delgado UniversidaddeLosAndes,Bogota,Colombia

B. Courbon,N. Godinovic, D. Lelas,I. Puljak, T. Sculac

Z. Antunovic, M. Kovac UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,D. Ferencek, K. Kadija,B. Mesic, A. Starodumov7, T. Susa

InstituteRudjerBoskovic,Zagreb,Croatia

M.W. Ather,A. Attikis, M. Kolosova, G. Mavromanolakis,J. Mousa, C. Nicolaou, F. Ptochos, P.A. Razis,

H. Rykaczewski UniversityofCyprus,Nicosia,Cyprus

M. Finger8, M. Finger Jr.8

CharlesUniversity,Prague,CzechRepublic

E. Ayala

EscuelaPolitecnicaNacional,Quito,Ecuador

E. Carrera Jarrin

UniversidadSanFranciscodeQuito,Quito,Ecuador

Y. Assran9,10,S. Elgammal10, S. Khalil11

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

S. Bhowmik, A. Carvalho Antunes De Oliveira,R.K. Dewanjee, K. Ehataht, M. Kadastik, M. Raidal,

C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola, H. Kirschenmann,J. Pekkanen,M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Havukainen, J.K. Heikkilä, T. Järvinen,V. Karimäki, R. Kinnunen, T. Lampén, K. Lassila-Perini,S. Laurila,

S. Lehti, T. Lindén,P. Luukka, T. Mäenpää, H. Siikonen,E. Tuominen, J. Tuominiemi

HelsinkiInstituteofPhysics,Helsinki,Finland

T. Tuuva

LappeenrantaUniversityofTechnology,Lappeenranta,Finland

M. Besancon, F. Couderc,M. Dejardin, D. Denegri, J.L. Faure, F. Ferri, S. Ganjour, A. Givernaud,

P. Gras, G. Hamel de Monchenault, P. Jarry,C. Leloup,E. Locci, J. Malcles,G. Negro, J. Rander,

A. Rosowsky, M.Ö. Sahin,M. Titov

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

A. Abdulsalam12,C. Amendola, I. Antropov, F. Beaudette, P. Busson, C. Charlot,

R. Granier de Cassagnac, I. Kucher, A. Lobanov, J. Martin Blanco, C. Martin Perez,M. Nguyen,

C. Ochando, G. Ortona,P. Paganini, P. Pigard, J. Rembser,R. Salerno,J.B. Sauvan, Y. Sirois,

A.G. Stahl Leiton, A. Zabi, A. Zghiche

LaboratoireLeprince-Ringuet,Ecolepolytechnique,CNRS/IN2P3,UniversitéParis-Saclay,Palaiseau,France

J.-L. Agram13, J. Andrea, D. Bloch,J.-M. Brom, E.C. Chabert, V. Cherepanov, C. Collard,E. Conte13,

J.-C. Fontaine13,D. Gelé, U. Goerlach, M. Jansová, A.-C. Le Bihan, N. Tonon,P. Van Hove

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,C. Bernet, G. Boudoul,N. Chanon, R. Chierici,D. Contardo, P. Depasse, H. El Mamouni,

J. Fay, L. Finco,S. Gascon, M. Gouzevitch, G. Grenier, B. Ille, F. Lagarde, I.B. Laktineh,H. Lattaud,

M. Lethuillier,L. Mirabito, S. Perries,A. Popov14,V. Sordini, G. Touquet, M. Vander Donckt, S. Viret

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

T. Toriashvili15

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze8

TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann,L. Feld, M.K. Kiesel, K. Klein, M. Lipinski,M. Preuten, M.P. Rauch,C. Schomakers, J. Schulz,

M. Teroerde,B. Wittmer

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

A. Albert, D. Duchardt, M. Erdmann,S. Erdweg, T. Esch, R. Fischer,S. Ghosh, A. Güth, T. Hebbeker,

C. Heidemann,K. Hoepfner,H. Keller, L. Mastrolorenzo,M. Merschmeyer, A. Meyer,P. Millet,

S. Mukherjee,T. Pook,M. Radziej, H. Reithler, M. Rieger, A. Schmidt,D. Teyssier, S. Thüer

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

G. Flügge,O. Hlushchenko, T. Kress, A. Künsken, T. Müller,A. Nehrkorn, A. Nowack, C. Pistone, O. Pooth,

D. Roy, H. Sert, A. Stahl16

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin,T. Arndt, C. Asawatangtrakuldee, I. Babounikau, K. Beernaert,O. Behnke, U. Behrens,

A. Bermúdez Martínez, D. Bertsche, A.A. Bin Anuar, K. Borras17,V. Botta, A. Campbell,P. Connor,

C. Contreras-Campana, V. Danilov,A. De Wit, M.M. Defranchis, C. Diez Pardos, D. Domínguez Damiani,

G. Eckerlin,T. Eichhorn, A. Elwood, E. Eren, E. Gallo18, A. Geiser, A. Grohsjean, M. Guthoff,M. Haranko,

A. Harb,J. Hauk, H. Jung,M. Kasemann, J. Keaveney, C. Kleinwort,J. Knolle, D. Krücker, W. Lange,

A. Lelek,T. Lenz, J. Leonard, K. Lipka,W. Lohmann19, R. Mankel, I.-A. Melzer-Pellmann,A.B. Meyer,

M. Meyer,M. Missiroli, G. Mittag, J. Mnich, V. Myronenko,S.K. Pflitsch, D. Pitzl,A. Raspereza,

M. Savitskyi,P. Saxena,P. Schütze, C. Schwanenberger, R. Shevchenko, A. Singh,H. Tholen, O. Turkot,

A. Vagnerini,G.P. Van Onsem, R. Walsh, Y. Wen,K. Wichmann,C. Wissing, O. Zenaiev

DeutschesElektronen-Synchrotron,Hamburg,Germany

R. Aggleton,S. Bein, L. Benato, A. Benecke, V. Blobel, T. Dreyer, A. Ebrahimi, E. Garutti, D. Gonzalez,

P. Gunnellini, J. Haller, A. Hinzmann, A. Karavdina, G. Kasieczka, R. Klanner, R. Kogler,N. Kovalchuk,

S. Kurz, V. Kutzner, J. Lange,D. Marconi,J. Multhaup, M. Niedziela, C.E.N. Niemeyer,D. Nowatschin,

A. Perieanu,A. Reimers, O. Rieger, C. Scharf,P. Schleper, S. Schumann, J. Schwandt,J. Sonneveld,

H. Stadie,G. Steinbrück, F.M. Stober,M. Stöver, A. Vanhoefer, B. Vormwald, I. Zoi

UniversityofHamburg,Hamburg,Germany

M. Akbiyik, C. Barth,M. Baselga,S. Baur, E. Butz, R. Caspart, T. Chwalek, F. Colombo, W. De Boer,

A. Dierlamm,K. El Morabit, N. Faltermann, B. Freund,M. Giffels,M.A. Harrendorf, F. Hartmann16,

S.M. Heindl,U. Husemann, F. Kassel16, I. Katkov14, S. Kudella, S. Mitra, M.U. Mozer, Th. Müller,

M. Plagge,G. Quast, K. Rabbertz, M. Schröder, I. Shvetsov,G. Sieber, H.J. Simonis, R. Ulrich, S. Wayand,

M. Weber, T. Weiler, S. Williamson,C. Wöhrmann, R. Wolf

G. Anagnostou, G. Daskalakis,T. Geralis,A. Kyriakis, D. Loukas, G. Paspalaki,I. Topsis-Giotis InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

G. Karathanasis,S. Kesisoglou, P. Kontaxakis, A. Panagiotou, I. Papavergou, N. Saoulidou, E. Tziaferi,

K. Vellidis

NationalandKapodistrianUniversityofAthens,Athens,Greece

K. Kousouris,I. Papakrivopoulos, G. Tsipolitis

NationalTechnicalUniversityofAthens,Athens,Greece

I. Evangelou, C. Foudas,P. Gianneios, P. Katsoulis, P. Kokkas, S. Mallios,N. Manthos, I. Papadopoulos,

E. Paradas, J. Strologas,F.A. Triantis, D. Tsitsonis

UniversityofIoánnina,Ioánnina,Greece

M. Bartók20,M. Csanad, N. Filipovic, P. Major, M.I. Nagy, G. Pasztor, O. Surányi, G.I. Veres

MTA-ELTELendületCMSParticleandNuclearPhysicsGroup,EötvösLorándUniversity,Budapest,Hungary

G. Bencze,C. Hajdu, D. Horvath21,Á. Hunyadi, F. Sikler,T.Á. Vámi, V. Veszpremi, G. Vesztergombi†

WignerResearchCentreforPhysics,Budapest,Hungary

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

InstituteofNuclearResearchATOMKI,Debrecen,Hungary

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

InstituteofPhysics,UniversityofDebrecen,Debrecen,Hungary

S. Choudhury, J.R. Komaragiri, P.C. Tiwari

IndianInstituteofScience(IISc),Bangalore,India

S. Bahinipati23, C. Kar,P. Mal, K. Mandal, A. Nayak24,D.K. Sahoo23,S.K. Swain

NationalInstituteofScienceEducationandResearch,HBNI,Bhubaneswar,India

S. Bansal, S.B. Beri,V. Bhatnagar, S. Chauhan,R. Chawla, N. Dhingra, R. Gupta, A. Kaur, M. Kaur, S. Kaur,

R. Kumar,P. Kumari, M. Lohan, A. Mehta, K. Sandeep, S. Sharma,J.B. Singh, A.K. Virdi, G. Walia

PanjabUniversity,Chandigarh,India

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

P. Priyanka, K. Ranjan,Aashaq Shah, R. Sharma

UniversityofDelhi,Delhi,India

R. Bhardwaj25,M. Bharti25,R. Bhattacharya,S. Bhattacharya, U. Bhawandeep25,D. Bhowmik, S. Dey,

S. Dutt25,S. Dutta, S. Ghosh,K. Mondal, S. Nandan, A. Purohit, P.K. Rout, A. Roy,S. Roy Chowdhury,

G. Saha,S. Sarkar, M. Sharan, B. Singh25, S. Thakur25

SahaInstituteofNuclearPhysics,HBNI,Kolkata,India

P.K. Behera

IndianInstituteofTechnologyMadras,Madras,India

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

T. Aziz,M.A. Bhat, S. Dugad, G.B. Mohanty, N. Sur, B. Sutar, Ravindra Kumar Verma TataInstituteofFundamentalResearch-A,Mumbai,India

S. Banerjee, S. Bhattacharya, S. Chatterjee,P. Das, M. Guchait,Sa. Jain, S. Karmakar, S. Kumar,

M. Maity26,G. Majumder, K. Mazumdar, N. Sahoo,T. Sarkar26

TataInstituteofFundamentalResearch-B,Mumbai,India

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

IndianInstituteofScienceEducationandResearch(IISER),Pune,India

S. Chenarani27, E. Eskandari Tadavani,S.M. Etesami27, M. Khakzad, M. Mohammadi Najafabadi,

M. Naseri, F. Rezaei Hosseinabadi, B. Safarzadeh28, M. Zeinali

InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran

M. Felcini,M. Grunewald

UniversityCollegeDublin,Dublin,Ireland

M. Abbresciaa,b, C. Calabriaa,b, A. Colaleoa, D. Creanzaa,c,L. Cristellaa,b, N. De Filippisa,c, M. De Palmaa,b, A. Di Florioa,b, F. Erricoa,b,L. Fiorea,A. Gelmia,b, G. Iasellia,c, M. Incea,b, S. Lezkia,b, G. Maggia,c,M. Maggia, G. Minielloa,b, S. Mya,b, S. Nuzzoa,b, A. Pompilia,b,

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

P. Verwilligena,G. Zitoa

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

G. Abbiendia,C. Battilanaa,b,D. Bonacorsia,b, L. Borgonovia,b,S. Braibant-Giacomellia,b,

R. Campaninia,b,P. Capiluppia,b,A. Castroa,b, F.R. Cavalloa, S.S. Chhibraa,b,C. Cioccaa,G. Codispotia,b,

M. Cuffiania,b,G.M. Dallavallea, F. Fabbria,A. Fanfania,b,E. Fontanesi, P. Giacomellia,C. Grandia,

L. Guiduccia,b,S. Lo Meoa,S. Marcellinia, G. Masettia, A. Montanaria, F.L. Navarriaa,b,A. Perrottaa, F. Primaveraa,b,16,A.M. Rossia,b, T. Rovellia,b,G.P. Sirolia,b, N. Tosia

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

S. Albergoa,b, A. Di Mattiaa,R. Potenzaa,b,A. Tricomia,b,C. Tuvea,b

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

G. Barbaglia,K. Chatterjeea,b,V. Ciullia,b,C. Civininia,R. D’Alessandroa,b, E. Focardia,b, G. Latino, P. Lenzia,b, M. Meschinia, S. Paolettia,L. Russoa,29, G. Sguazzonia,D. Stroma, L. Viliania

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

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

INFNLaboratoriNazionalidiFrascati,Frascati,Italy

F. Ferroa, F. Raveraa,b, E. Robuttia,S. Tosia,b

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

A. Benagliaa,A. Beschib,F. Brivioa,b,V. Cirioloa,b,16, S. Di Guidaa,b,16, M.E. Dinardoa,b,S. Fiorendia,b, S. Gennaia,A. Ghezzia,b,P. Govonia,b,M. Malbertia,b,S. Malvezzia,A. Massironia,b,D. Menascea, F. Monti, L. Moronia, M. Paganonia,b,D. Pedrinia, S. Ragazzia,b, T. Tabarelli de Fatisa,b,D. Zuoloa,b

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

S. Buontempoa, N. Cavalloa,c, A. De Iorioa,b,A. Di Crescenzoa,b, F. Fabozzia,c,F. Fiengaa, G. Galatia, A.O.M. Iorioa,b, W.A. Khana,L. Listaa, S. Meolaa,d,16, P. Paoluccia,16, C. Sciaccaa,b, E. Voevodinaa,b

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

P. Azzia,N. Bacchettaa,D. Biselloa,b,A. Bolettia,b,A. Bragagnoloa,b, R. Carlina,b, M. Dall’Ossoa,b,

P. De Castro Manzanoa, T. Dorigoa,U. Dossellia, F. Gasparinia,b, U. Gasparinia,b,A. Gozzelinoa,

S.Y. Hoha,b,S. Lacapraraa, P. Lujana,M. Margonia,b,A.T. Meneguzzoa,b, F. Montecassianoa, J. Pazzinia,b, N. Pozzobona,b_{,P. Ronchese}a,b_{, R. Rossin}a,b_{, A. Tiko}a_{,E. Torassa}a_{, M. Zanetti}a,b_,

P. Zottoa,b, G. Zumerlea,b

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

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

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

M. Biasinia,b, G.M. Bileia,C. Cecchia,b,D. Ciangottinia,b,L. Fanòa,b,P. Laricciaa,b, R. Leonardia,b, E. Manonia, G. Mantovania,b, V. Mariania,b,M. Menichellia,A. Rossia,b,A. Santocchiaa,b, D. Spigaa

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

K. Androsova,P. Azzurria,G. Bagliesia,L. Bianchinia,T. Boccalia,L. Borrello, R. Castaldia, M.A. Cioccia,b, R. Dell’Orsoa,G. Fedia, F. Fioria,c, L. Gianninia,c,A. Giassia, M.T. Grippoa,F. Ligabuea,c, E. Mancaa,c, G. Mandorlia,c, A. Messineoa,b, F. Pallaa,A. Rizzia,b, 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,D. Del Rea,b, E. Di Marcoa,b, M. Diemoza,S. Gellia,b,

E. Longoa,b, B. Marzocchia,b,P. Meridiania, G. Organtinia,b,F. Pandolfia, R. Paramattia,b, F. Preiatoa,b, S. Rahatloua,b,C. Rovellia,F. Santanastasioa,b

a_{INFNSezionediRoma,Rome,Italy} b_{SapienzaUniversitàdiRoma,Rome,Italy}

N. Amapanea,b_{, R. Arcidiacono}a,c_{,S. Argiro}a,b_{,M. Arneodo}a,c_{,N. Bartosik}a_{,R. Bellan}a,b_{, C. Biino}a_, N. Cartigliaa, F. Cennaa,b,S. Comettia,M. Costaa,b, R. Covarellia,b,N. Demariaa,B. Kiania,b,C. Mariottia, S. Masellia, E. Migliorea,b,V. Monacoa,b,E. Monteila,b,M. Montenoa, M.M. Obertinoa,b,L. Pachera,b, N. Pastronea,M. Pelliccionia, G.L. Pinna Angionia,b,A. Romeroa,b, M. Ruspaa,c, R. Sacchia,b,

K. Shchelinaa,b, V. Solaa, A. Solanoa,b,D. Soldia,b,A. Staianoa

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

c_{UniversitàdelPiemonteOrientale,Novara,Italy}

S. Belfortea,V. Candelisea,b,M. Casarsaa, F. Cossuttia,A. Da Rolda,b,G. Della Riccaa,b, F. Vazzolera,b,

A. Zanettia

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

D.H. Kim,G.N. Kim, M.S. Kim, J. Lee,S. Lee, S.W. Lee, C.S. Moon, Y.D. Oh, S.I. Pak,S. Sekmen,

D.C. Son,Y.C. Yang

KyungpookNationalUniversity,Daegu,RepublicofKorea

H. Kim,D.H. Moon,G. Oh

ChonnamNationalUniversity,InstituteforUniverseandElementaryParticles,Kwangju,RepublicofKorea

B. Francois,J. Goh30,T.J. Kim

HanyangUniversity,Seoul,RepublicofKorea

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

Y. Roh

KoreaUniversity,Seoul,RepublicofKorea

H.S. Kim

SejongUniversity,Seoul,RepublicofKorea

J. Almond,J. Kim, J.S. Kim, H. Lee,K. Lee, K. Nam,S.B. Oh, B.C. Radburn-Smith, S.h. Seo, U.K. Yang,

H.D. Yoo,G.B. Yu

SeoulNationalUniversity,Seoul,RepublicofKorea

D. Jeon, H. Kim,J.H. Kim, J.S.H. Lee, I.C. Park

UniversityofSeoul,Seoul,RepublicofKorea

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

SungkyunkwanUniversity,Suwon,RepublicofKorea

V. Dudenas, A. Juodagalvis,J. Vaitkus

VilniusUniversity,Vilnius,Lithuania

I. Ahmed,Z.A. Ibrahim, M.A.B. Md Ali31,F. Mohamad Idris32,W.A.T. Wan Abdullah, M.N. Yusli,

Z. Zolkapli

NationalCentreforParticlePhysics,UniversitiMalaya,KualaLumpur,Malaysia

J.F. Benitez, A. Castaneda Hernandez,J.A. Murillo Quijada

UniversidaddeSonora(UNISON),Hermosillo,Mexico

H. Castilla-Valdez,E. De La Cruz-Burelo, M.C. Duran-Osuna, I. Heredia-De La Cruz33,R. Lopez-Fernandez,

J. Mejia Guisao,R.I. Rabadan-Trejo,M. Ramirez-Garcia, G. Ramirez-Sanchez, R. Reyes-Almanza,

A. Sanchez-Hernandez

CentrodeInvestigacionydeEstudiosAvanzadosdelIPN,MexicoCity,Mexico

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

UniversidadIberoamericana,MexicoCity,Mexico

J. Eysermans,I. Pedraza, H.A. Salazar Ibarguen, C. Uribe Estrada

BenemeritaUniversidadAutonomadePuebla,Puebla,Mexico

A. Morelos Pineda