Search for lepton-flavour-violating decays of the Higgs boson

Physics Letters B 749 (2015) 337–362

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

lepton-flavour-violating

decays

of

the

Higgs

boson

.CMSCollaboration CERN,Switzerland

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

Articlehistory:

Received25February2015 Receivedinrevisedform20July2015 Accepted21July2015

Availableonline26July2015 Editor:M.Doser Keywords: CMS Physics Higgs Muons Taus Lepton-flavour-violation

Thefirstdirectsearchforlepton-flavour-violatingdecaysoftherecentlydiscoveredHiggsboson(H)is

described.Thesearchis performedintheH→μτe and H→μτh channels,where τe and τh are tau

leptonsreconstructedintheelectronicandhadronicdecaychannels,respectively.Thedatasampleused

inthissearch wascollectedinpp collisionsatacentre-of-mass energyof√s=8 TeV withtheCMS

experimentattheCERNLHCandcorrespondstoanintegratedluminosityof19.7 fb−1.Thesensitivity

of the search is an order of magnitude better than the existing indirect limits. A slight excess of

signal eventswithasignificance of2.4standard deviations isobserved.The p-value ofthisexcessat

MH=125 GeV is0.010.ThebestfitbranchingfractionisB(H→μτ)= (0.84+₋0.390.37)%.Aconstraintonthe branchingfraction,B(H→μτ)<1.51% at95%confidencelevelisset.Thislimitissubsequentlyusedto constrainthe μ–τYukawacouplingstobelessthan3.6×10−3_.

©2015CERNforthebenefitoftheCMSCollaboration.PublishedbyElsevierB.V.Thisisanopenaccess

articleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

ThediscoveryoftheHiggsboson(H)[1–3]hasgeneratedgreat interest in exploring its properties. In the standard model (SM), lepton-flavour-violating (LFV) decays are forbidden if the theory isto be renormalizable [4]. Ifthisrequirement isrelaxed, so the theory is valid only to a finite mass scale, then LFV couplings maybeintroduced.LFVdecayscanoccurnaturallyinmodelswith morethan oneHiggsdoubletwithoutabandoning renormalizabil-ity[5].Theyalsoariseinsupersymmetricmodels[6–9],composite Higgsbosonmodels[10,11],modelswithflavoursymmetries[12], Randall–Sundrummodels [13–15], andmanyothers[16–23].The presenceofLFVcouplingswouldallow μ →e, τ→μand τ→e transitionsto proceed via a virtual Higgsboson [24,25].The ex-perimental limits on these have recently been translated into constraintson the branchingfractions B(H→eμ, μτ, eτ) [4,26]. The μ →e transition is strongly constrained by null search re-sultsfor μ →eγ [27], B(H→μe) <O(10−8).However, the con-straintson τ→μand τ→e aremuchlessstringent.Thesecome fromsearchesfor τ→μγ [28,29]and other rare τ decays [30], τ →eγ, μ and eg−2 measurements [27]. Exclusion limits on theelectronandmuonelectricdipole moments[31] alsoprovide complementaryconstraints.Theseleadtothemuchlessrestrictive limits: B(H→μτ) <O(10%), B(H→eτ) <O(10%). The obser-vationofthe Higgsbosonoffersthe possibilityofsensitivedirect

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

searchesforLFVHiggsbosondecays.Todatenodedicatedsearches have been performed. However, a theoretical reinterpretation of the ATLAS H→τ τ search results in terms of LFV decays by an independent group hasbeen usedto set limitsatthe 95% confi-dencelevel(CL)of B(H→μτ) <13%, B(H→eτ) <13%[4].

ThisletterdescribesasearchforaLFVdecayofaHiggsboson withMH=125 GeV attheCMSexperiment.The2012dataset

col-lectedatacentre-of-massenergyof√s=8 TeV correspondingto an integrated luminosity of19.7 fb−1 is used.The search is per-formedintwochannels,H→μτeandH→μτh,where τeand τh

are tau leptons reconstructed in the electronic and hadronic de-caychannels, respectively.ThesignatureisverysimilartotheSM H→τμτeandH→τμτhdecays,where τμ isa taulepton

decay-ing muonically, whichhavebeen studiedby CMSin Refs. [32,33] andATLASinRef.[34],butwithsomesignificantkinematic differ-ences.The μcomespromptlyfromtheLFVH decayandtendsto havea largermomentum thanin theSM case. Thereis onlyone tauleptonsotherearetypicallyfewerneutrinosinthedecay.They arehighlyLorentzboostedandtendtobecollinearwiththevisible τ decayproducts.

The two channels are divided into categories based on the number of jets in order to separate the different H boson pro-duction mechanisms. The signal sensitivity is enhanced by using different selection criteria for each category. The dominant pro-ductionmechanismis gluon–gluonfusion butthereisalso a sig-nificantcontributionfromvectorboson fusionwhichisenhanced by requiringjetsto be presentin theevent. The dominant back-groundin the H→μτe channel is Z→τ τ.Other much smaller

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0370-2693/©2015CERNforthebenefitoftheCMSCollaboration.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

backgrounds come from misidentified leptons in W+jets, QCD multijets and tt events. In the H→μτh channel the dominant

backgroundarisesfrommisidentified τ leptons in W+jets, QCD multijets and tt events. Less significant backgrounds come from Z→τ τ andZ+jets.Theprincipalbackgroundsareestimated us-ingdata.ThereisalsoasmallbackgroundfromSMH decayswhich isestimatedwithsimulation.Thepresenceorabsenceofasignalis establishedbyfittingamassdistributionforsignalandbackground usingthe asymptoticCLs criterion [35,36].A “blind”analysiswas

performed. The data in the signal region were not studied until theselectioncriteriahadbeenfixedandthebackgroundestimate finalized.

2. Detectoranddatasets

AdetaileddescriptionoftheCMSdetector,togetherwitha de-scriptionofthecoordinatesystemusedandtherelevantkinematic variables,canbefoundinRef.[37].Themomentaofcharged parti-clesaremeasuredwithasiliconpixelandstriptrackerthatcovers thepseudorapidityrange|η|<2.5 andisinsidea3.8 T axial mag-netic field. Surrounding the tracker are a lead tungstate crystal electromagneticcalorimeter(ECAL)andabrass/scintillatorhadron calorimeter,bothconsistingofabarrelassemblyandtwoendcaps thatextendtoapseudorapidityrangeof|η| <3.0.A steel/quartz-fiberCherenkovforwarddetectorextendsthecalorimetriccoverage to|η| <5.0.TheoutermostcomponentoftheCMSdetectoristhe muonsystem, consistingofgas-ionization detectorsplacedinthe steelflux-returnyokeof themagnettomeasure themomenta of muonstraversing the detector.The two-level CMStrigger system selects eventsof interest forpermanent storage.The firsttrigger level,composedofcustom hardware processors,usesinformation fromthecalorimetersandmuondetectorstoselecteventsinless than 3.2 μs. The high-level trigger software algorithms, executed onafarmofcommercialprocessors,furtherreducetheeventrate usinginformationfromalldetectorsubsystems.

TheH→μτhchannel selectionbeginsbyrequiringasingle μ

trigger with a transverse momentum threshold pμ_T >24 GeV in the pseudorapidity range |η| <2.1, while the H→μτe channel

requiresa μ–e triggerwithpTthresholdsof17 GeV (|η| <2.4)for

the μand8 GeV (|η| <2.5) forthee. Loose e and μ identifica-tion criteriaare applied atthe triggerlevel. The leptons are also requiredto be isolated fromother tracks andcalorimeter energy depositstomaintainanacceptabletriggerrate.

Simulated samples of signal and background events are pro-ducedusingvarious MonteCarlo(MC) eventgenerators, withthe CMSdetector response modeled with Geant4 [38].Higgs bosons areproducedinproton–protoncollisionspredominantlybygluon– gluon fusion, but also by vector boson fusion andin association witha W or Z boson. Itis assumedthat the rateofnewdecays oftheH aresufficiently smallthat thenarrowwidth approxima-tion can be used. The LFV H decay samples are produced with pythia 8.175 [39]. The background event samples with a SM H are generated by powheg 1.0 [40–44] with the τ decays mod-eled by tauola[45].The MadGraph 5.1[46] generatorisusedfor Z+jets,W+jets,tt,anddibosonproduction,and powheg for sin-gletop-quarkproduction.The powheg and MadGraph generators areinterfacedwith pythia forpartonshowerandfragmentation.

3. Eventreconstruction

A particle-flow (PF) algorithm [47,48] combines the informa-tion from all CMS sub-detectors to identify and reconstruct the individual particles emerging from all vertices: charged hadrons, neutralhadrons,photons,muons,andelectrons.Theseparticlesare then usedto reconstructjets, hadronic τ decays,andtoquantify

the isolation ofleptons andphotons. The missingtransverse en-ergy vector is the negative vector sum of all particle transverse momenta and its magnitudeis referred to as Emiss

T . The variable R=(η)2_{+ (φ)}2 _{isusedtomeasuretheseparationbetween}

reconstructed objects in the detector, where φ is the azimuthal angle(inradians)ofthetrajectoryoftheobjectintheplane trans-versetothedirectionoftheprotonbeams.

The large number of proton interactions occurring per LHC bunchcrossing(pileup),withanaverageof21in2012,makesthe identification of the vertex corresponding to the hard-scattering process nontrivial. This affects mostof the object reconstruction algorithms: jets,lepton isolation, etc. The trackingsystemis able to separate collision vertices ascloseas0.5 mm along thebeam direction[49].Foreach vertex,thesumofthep2_T ofall tracks as-sociated withthe vertex is computed. The vertex forwhich this quantity is the largest is assumed to correspond to the hard-scatteringprocess,andisreferredtoastheprimaryvertexinthe eventreconstruction.

Muons are reconstructed using two algorithms [50]: one in which tracks inthe silicon trackerare matched to signalsin the muon detectors, and another in which a global track fit is per-formed, seeded by signals inthe muon systems.The muon can-didates used in the analysis are required to be successfully re-constructed by both algorithms. Furtheridentificationcriteriaare imposed onthe muoncandidatesto reduce thefractionoftracks misidentified as muons. These include the number of measure-ments in thetracker andinthe muon systems,the fitquality of theglobalmuontrackanditsconsistencywiththeprimaryvertex. Electron reconstruction requires the matching of an energy cluster in the ECAL with a track in the silicon tracker [51,52]. Identification criteria based on the ECAL shower shape, match-ing betweenthetrackandtheECALcluster, andconsistencywith theprimaryvertexareimposed.Electronidentificationreliesona multivariate technique thatcombines observablessensitiveto the amount ofbremsstrahlung alongthe electron trajectory, the geo-metricalandmomentummatchingbetweentheelectrontrajectory andassociatedclusters,aswellasshower-shapeobservables. Addi-tionalrequirementsareimposedtoremoveelectrons producedby photonconversions.

JetsarereconstructedfromallthePFobjectsusingtheanti-kT

jet clustering algorithm [53] implemented in FastJet [54], with a distance parameter of 0.5. The jet energy is corrected for the contribution ofparticlescreatedin pileupinteractions andinthe underlying event. Particles from different pileup vertices can be clusteredinto a pileupjet, orsignificantly overlapa jet fromthe primary vertex below the pT threshold applied in the analysis.

Suchjetsareidentifiedandremoved[55].

Hadronically decaying τ leptons are reconstructed and iden-tified using the hadron plus strips (HPS) algorithm [56] which targets the main decay modes by selecting PF candidates with one charged hadron and up to two neutralpions, or with three chargedhadrons.Aphotonfroma neutral-piondecaycanconvert inthetrackermaterialintoan electronandapositron,whichcan then radiate bremsstrahlungphotons. These particles give rise to several ECALenergy depositsat thesame η value andseparated in azimuthal angle, andare reconstructed as several photonsby the PF algorithm. To increase the acceptance forsuch converted photons, the neutralpionsare identified by clustering the recon-structedphotonsinnarrowstripsalongtheazimuthaldirection.

4. Eventselection

The eventselectionconsistsofthreesteps.First,aloose selec-tion defining the basic signature is applied. The sample is then divided into categories, according to the number of jets in the

CMS Collaboration / Physics Letters B 749 (2015) 337–362 339

Table 1

Selectioncriteriaforthekinematicvariablesafterthelooseselection. Variable

[GeV]

H→μτe H→μτh

0-jet 1-jet 2-jet 0-jet 1-jet 2-jet

pμT> 50 45 25 45 35 30 peT> 10 10 10 – – – pτh T > – – – 35 40 40 MeT< 65 65 25 – – – MμT> 50 40 15 – – – Mτh T < – – – 50 35 35 [radians] φ_pμ T−p τh T > – – – 2.7 – – φ_pe T−EmissT < 0.5 0.5 0.3 – – – φ_pe T−p μ T > 2.7 1.0 – – – –

event.Finally,requirementsare placedonasetofkinematic vari-ablesdesignedtosuppressthebackgrounds.

Theloose selection forthe H→μτe channel requiresan

iso-lated μ (pT>25 GeV, |η| <2.1) andan isolatede (pT>10 GeV,

|η| <2.3) of opposite charge lying within a region of the detec-torthatallowsgoodidentification.Thee and μarerequiredtobe separatedby R >0.1.TheH→μτhchannelrequiresanisolated

μ(pT>30 GeV, |η| <2.1) andan isolatedhadronically decaying

τ (pT>30 GeV,|η| <2.3)ofoppositecharge.Leptonsarealso

re-quiredto beisolatedfromanyjetintheeventwith pT>30 GeV

by R >0.4 andtohaveanimpactparameterconsistentwiththe primaryvertex.

Theeventsarethendividedintocategorieswithineachchannel accordingto thenumberofjetsintheevent. Jetsarerequiredto passidentification criteria[55], have pT>30 GeV and lie within

the range|η| <4.7. The zero jet category contains signal events predominantlyproduced by gluon–gluon fusion. The one-jet cat-egory contains signal events predominantly produced by gluon– gluonfusionandanegligiblysmallnumberofeventsproducedin associationwithaWorZbosondecayinghadronically.Thetwojet categoryisenrichedwithsignaleventsproducedby vectorboson fusion.

Themainvariableforthediscriminationbetweenthesignaland backgroundisthecollinearmass,Mcol,whichprovidesan

estima-torofthereconstructedH massusingtheobserveddecayproducts. Thisisconstructedusingthecollinearapproximation[57]whichis based on the observation that since the mass ofthe H is much greater thanthe mass ofthe τ, the τ decay products are highly Lorentzboostedinthedirectionofthe τ.Theneutrinomomenta canbeapproximatedtobeinthesamedirectionastheother vis-ible decay products of the τ and the component ofthe missing transverseenergyin thetransverse directionofthe visible τ de-cayproductsisusedtoestimate thetransversecomponentofthe neutrino momentum. Fig. 1 shows Mcol distribution for the

sig-naland background comparedto data for each of thecategories ineach channelafterthelooseselection.Thesimulatedsignalfor B(H→μτ) =100% isshown. Theprincipalbackgroundsare esti-matedwithdatausingtechniquesdescribedinSection 5.Thereis goodagreementbetweendataandthebackgroundestimation.The agreementissimilarinallofthekinematicvariablesthatare sub-sequentlyusedtosuppressbackgrounds.Theanalysisisperformed “blinded”intheregion100 <Mcol<150 GeV.

Next, a set of kinematic variables is defined and the criteria forselection aredetermined by optimizingforS/√S+B where S andBaretheexpectedsignalandbackgroundeventyieldsinthe masswindow100 <Mcol<150 GeV.Thesignaleventyield

corre-sponds to the SM H production cross section at MH=125 GeV

with B(H→μτ) =10%. This value for the LFV H branching

fraction is chosen because it corresponds to the limit from in-direct measurements as described in Ref. [4]. The optimization was also performed assuming B(H→μτ) =1% and negligible change in the optimal values of selection criteria was observed. The criteria for each category, and in each channel, are given in Table 1. The variables used are the lepton transverse mo-menta p_T with  =τh, μ, e; azimuthal angles between the

lep-tons φ_

p1_T−p2_T ; azimuthal angle φpT−E miss

T ; thetransverse mass

M

T=

 2p

TEmissT (1−cosφp

T−EmissT ). Events inthe 2-jetcategory

are required to havetwo jetsseparated by a pseudorapidity gap (|η| >3.5) and to have a dijet invariant mass greater than 550 GeV. In the H→μτe channel events in which at least one

ofthejetsidentifiedascomingfromab-quarkdecayareusingthe combinedsecondary-vertexb-taggingalgorithm[58]arevetoed,to suppressbackgroundsfromtopquarkdecays.

5. Backgroundprocesses

Thecontributionsofthedominantbackgroundprocessesare es-timatedwithdatawhilelesssignificantbackgroundsareestimated usingsimulation.ThelargestbackgroundscomefromZ→τ τ and frommisidentified leptons inW+jets andQCD multijet produc-tion.

5.1. Z→τ τ

TheZ→τ τ backgroundcontributionisestimatedusingan em-beddingtechnique[33,59]asfollows.AsampleofZ→μμevents istakenfromdatausinga loose μ selection. Thetwo muonsare then replaced withPFparticles resultingfrom thereconstruction ofsimulated τ leptondecays.Thus, thekeyfeatures oftheevent topology such as the jets, missing transverse energy and under-lying event are taken directly fromdata with onlythe τ decays beingsimulated.Thenormalizationofthesampleisobtainedfrom thesimulation.Thetechniqueisvalidatedbycomparingthe τ lep-ton identificationefficiencies estimatedwith an embedded decay sample,usingsimulatedZ→μμevents,tothosefromsimulated Z→τ τ decays.

5.2. Misidentifiedleptons

LeptonscanarisefrommisidentifiedPFobjectsinW+jets and QCD multijetprocesses. This background is estimated with data. A sample with similar kinematicproperties to the signal sample butenriched in W+jets and QCD multijets isdefined. Then the probability forPF objects to be misidentified asleptons is mea-sured inan independent data set,andthis probability isapplied totheenrichedsample tocomputethemisidentifiedlepton back-groundinthesignalregion.Thetechniqueisshownschematically in Table 2 in whichfour regions aredefinedincluding thesignal and background enriched regions and two control regions used forvalidation ofthe technique. Itis employed slightlydifferently in theH→μτe and H→μτh channels. The leptonisolation

re-quirements used to define the enriched regions in each channel areslightlydifferent.

IntheH→μτechannel,regionIisthesignalregioninwhich

an isolated μ andanisolated e are required.RegionIII isa data sample inwhichall theanalysisselectioncriteriaare applied ex-cept that one of theleptons isrequired tobe not-isolated. Thus, there are two components: events with an isolated μ and not-isolated e events, aswell as eventswith an isolated e and not-isolated μ events.There is negligiblenumber ofsignal events in regionIII.RegionsIIandIVaredatasamplesformedwiththesame

Fig. 1. DistributionsofthecollinearmassMcolforsignalwithB(H→μτ)=100% forclarity,andbackgroundprocessesafterthelooseselectionrequirementsfortheLFV H→μτ candidatesforthedifferentchannelsandcategoriescomparedtodata.Theshadedgreybandsindicatethetotaluncertainty.Thebottompanelineachplotshows thefractionaldifferencebetweentheobserveddataandthetotalestimatedbackground.Topleft:H→μτe0-jet;topright:H→μτh 0-jet;middleleft:H→μτe1-jet; middleright:H→μτh1-jet;bottomleft:H→μτe2-jet;bottomrightH→μτh2-jet.

selectioncriteriaasregionsIandIII,respectively,butwith same-signratherthanopposite-signleptons.Thekinematicdistributions of the same-sign samples are very similar to the opposite-sign samples.

The sample in region III is dominated by W+jets and QCD multijetsbutwithsmallcontributionsfromWW, ZZ andWZ that

are subtracted usingsimulation. The misidentified μ background inregionIisthenestimatedbymultiplyingtheeventyieldin re-gion IIIbyafactor fμ· trigger,where fμ istheratioofnot-isolated

to isolated μ’s. It is computed in an independent data sample Z→μμ+X ,whereX isanobjectidentifiedasa μ,inbinsof pT

CMS Collaboration / Physics Letters B 749 (2015) 337–362 341

Fig. 2. DistributionsofMcolforregionIIcomparedtotheestimatefromscalingtheregionIVsamplebythemeasuredmisidentificationrates.Thebottompanelineachplot showsthefractionaldifferencebetweentheobserveddataandtheestimate.Left:H→μτe.Right:H→μτh.

Table 2

Schematictoillustratetheapplicationofthemethodusedtoestimatethe misiden-tifiedlepton()background.Samplesaredefinedbythechargeofthetwoleptons andbytheisolationrequirementsoneach.Chargedconjugatesareassumed.

Region I Region II

+1(isolated) +1(isolated)

−2(isolated) +2(isolated)

Region III Region IV

+1(isolated) +1(isolated)

−2(not-isolated) +2(not-isolated)

WW, ZZ andWZ using simulatedsamples.A correction trigger is

madetoaccount forthedifference intrigger efficiencyfor selec-tionofeventswithisolatede andnot-isolated μversustheevents withisolated e andisolated μ.Themisidentified e backgroundis computedinexactly thesameway.Thetechnique isvalidatedby usingthesame-signdatafromregionsIIandIVasshown schemat-icallyin Table 2.In Fig. 2(left)theobserveddatayieldinregion II is compared to the estimate from scaling the region IV sample by the measured misidentification rates. The region II sample is dominatedbymisidentifiedleptonsbutalsoincludessmall contri-butionsoftrueleptonsarisingfromvectorbosondecays,estimated withsimulatedsamples.

In the H→μτh channel, the τh candidate can come from a

misidentified jet with a number of sources, predominantly W+

jets and QCD multijets, but also Z→μμ+jets and tt. In this case the enriched background regions are defined with τh

can-didatesthat pass a looserisolation requirement, butdo not pass thesignal isolation requirement. The misidentificationrate fτh is

thendefinedasthefractionof τhcandidateswiththelooser

isola-tionthatalsopassthesignalisolationrequirement.Itismeasured in observed Z→μμ+X events, where X is an object identi-fiedasa τh.The misidentificationratemeasured inZ→μμ+X

datais checked by comparing to that measured in Z→μμ+X

simulationandfoundtobe ingoodagreement.The misidentified backgroundinthe signal region (regionI) isestimatedby multi-plyingthe eventyieldin regionIII by afactor fτh/(1−fτh).The

procedureisvalidatedwithsame-sign μτ eventsinthesameway asfortheH→μτechannel above. Fig. 2(right)showsthedatain

regionII comparedto theestimate fromscaling regionIVby the misidentificationrates.

The method assumes that the misidentification rate in Z→ μμ+X events is the same as forW+jets and QCD processes. Totestthisassumptionthemisidentificationratesaremeasuredin a QCD jet data control sample. Theyare found to be consistent. Finally asa cross-check the study has beenperformed also asa functionofthenumberofjetsintheeventandsimilaragreement isfound.

5.3. Otherbackgrounds

The SM H decays in the H→τ τ channel provide a small backgroundthat isestimatedwithsimulation.Thisbackground is suppressed by the kinematic selection criteria and peaks below 125 GeV. The W leptonic decay from tt produces opposite-sign dileptonsand Emiss_T .Thisbackgroundisestimatedwithsimulated

tt eventsusingtheshapeoftheMcol distributionfromsimulation

andadatacontrol regionfornormalization.The controlregion is the2-jetselectionbutwiththeadditionalrequirementthatatleast oneofthejetsisb-taggedinordertoenhancethett contribution.

Other smallerbackgrounds comefrom WW,ZZ+jets, Wγ +jets andsingle top-quarkproduction. Eachoftheseis estimatedwith simulation.

6. Systematicuncertainties

To set upper bounds on the signal strength, or determine a signalsignificance,weusetheCLs method[35,36].Abinned

like-lihood is used, based on the distributions of Mcol for the signal

andthe various backgroundsources. Systematicuncertainties are represented by nuisance parameters, some of which only affect thebackgroundandsignalnormalizations,whileothersaffectthe shapeand/ornormalizationoftheMcol distributions.

6.1. Normalizationuncertainties

Theuncertaintiesaresummarizedin Tables 3 and 4.The uncer-tainties inthe e and μ selection efficiency(trigger,identification andisolation) areestimated usingthe“tag andprobe” technique inZ→ee, μμdata[59].Theidentificationefficiencyofhadronic τ decaysisestimatedusingthe“tagandprobe”techniqueinZ→τ τ

Table 3

Systematicuncertaintiesintheexpectedeventyieldin%.Alluncertaintiesaretreatedascorrelatedbetweenthecategories,exceptwheretherearetwonumbers.Inthis casethenumberdenotedwith*istreatedasuncorrelatedbetweencategoriesandthetotaluncertaintyisthesuminquadratureofthetwonumbers.

Systematic uncertainty H→μτe H→μτh

0-Jet 1-Jet 2-Jet 0-Jet 1-Jet 2-Jet

Electron trigger/ID/isolation 3 3 3 – – –

Muon trigger/ID/isolation 2 2 2 2 2 2

Hadronic tau efficiency – – – 9 9 9

Luminosity 2.6 2.6 2.6 2.6 2.6 2.6 Z→τ τ background 3+3∗ 3+5∗ 3+10∗ 3+5∗ 3+5∗ 3+10∗ Z→μμ,ee background 30 30 30 30 30 30 Misidentifiedμ,e background 40 40 40 – – – Misidentifiedτhbackground – – – 30+10∗ 30 30 WW,ZZ+jets background 15 15 15 15 15 65 tt background 10 10 10+10∗ 10 10 10+33∗ W+γ background 100 100 100 – – – b-tagging veto 3 3 3 – – –

Single top production background 10 10 10 10 10 10

Table 4

Theoreticaluncertaintiesin%forHiggsbosonproduction.Anticorrelationsariseduetomigrationofeventsbetweenthecategoriesandareexpressedasnegativenumbers.

Systematic uncertainty Gluon-gluon fusion Vector boson fusion

0-Jet 1-Jet 2-Jet 0-Jet 1-Jet 2-Jet

Parton distribution function +9.7 +9.7 +9.7 +3.6 +3.6 +3.6

Renormalization/factorization scale +8 +10 −30 +4 +1.5 +2

Underlying event/parton shower +4 −5 −10 +10 <1 −1

Table 5

Systematicuncertaintiesin%fortheshapeofthesignalandbackgroundtemplates.

Systematic uncertainty H→μτe H→μτh

Hadronic tau energy scale – 3

Jet energy scale 3–7 3–7

Unclustered energy scale 10 10

Z→τ τ bias 100 –

data[56]. Theuncertaintyinthe Z→τ τ backgroundcomes pre-dominantlyfromtheuncertaintyinthe τ efficiency.The uncertain-tiesinthe estimationofthemisidentified leptonratecome from the difference in rates measured in differentdata samples (QCD multijets and W+jets). The uncertainty in the production cross section of the backgrounds that have been estimatedby simula-tionisalsoincluded.

Thereare severaluncertaintiesonthe H productioncross sec-tion, which depend on the production mechanism contribution and the analysis category. They are given in Table 4. These af-fecttheLFVH andtheSMH backgroundequally,andaretreated as 100% correlated. The parton distribution function (PDF) un-certainty is evaluated by comparing the yields in each category, whenspanning the parameterrangeofa numberofdifferent in-dependentPDF setsincludingCT10[60],MSTW[61],NNPDF[62] asrecommended by PDF4LHC [63]. The scale uncertaintyis esti-matedbyvaryingtherenormalization, μR,andfactorizationscales, μF, up and down by one half or two times the nominal scale (μR =μF =MH/2) under the constraint 0.5 <μF/μR <2 [64]. Theunderlyingeventandpartonshower uncertaintyisestimated by usingtwo different pythia tunes,AUET2 andZ2*. Anticorrela-tionsariseduetomigrationofeventsbetweenthecategoriesand areexpressedasnegativenumbers.

6.2. Mcolshapeuncertainties

Thesystematicuncertaintiesthatleadtoachangeintheshape of the Mcol distribution are summarized in Table 5. In the

em-bedded Z→τ τ Mcol distribution, used to estimate the Z→τ τ

background,a1%shifthasbeenobservedwithrespecttoZ→τ τ

simulationsbycomparingthemeansofbothdistributions.This oc-cursonlyintheH→μτechannel.The Mcol distributionhasbeen

corrected for this effect and a 100% uncertainty on this shift is usedasasystematicuncertaintyforthepossiblebias.Thejet en-ergyscalehasbeenstudiedextensivelyandastandardprescription forcorrections[65] is usedinall CMSanalyses.The overall scale is set using γ +jets events and the mostsignificant uncertainty arisesfromthephotonenergyscale.Anumberofother uncertain-tiessuchasjetfragmentationmodeling,singlepionresponseand uncertainties in the pileup correctionsare also included.The jet energy scaleuncertainties (3–7%) areapplied asa functionof pT

and η, including all correlations, to all jets in the event, propa-gatedtothemissingenergy,andtheresultant Mcol distributionis

used inthefit.Thereisalso anadditionaluncertaintyto account forthe unclusteredenergyscale uncertainty.The unclustered en-ergycomes fromjetsbelow10 GeV andPFcandidatesnotwithin jets. Itisalso propagatedtothe missingtransverseenergy.These effects cause a shiftof the Mcol distribution. The τ energy scale

isestimatedbycomparingZ→τ τ eventsindataandsimulation. An uncertaintyof3% isderived fromthiscomparison. The uncer-taintyisappliedbyshiftingthepTofthe τ candidatesintheevent

andusingtheresultantMcoldistributioninthefit.Finally,theMcol

distributions used inthefit havea statisticaluncertaintyineach massbinthatisincludedasan uncertaintywhichisuncorrelated betweenthebins.

Potentialuncertaintiesintheshapeofthemisidentifiedlepton backgrounds havealso been considered.In the H→μτe channel

themisidentified leptonrates fμ, fe aremeasuredandappliedin

bins oflepton pT and η. Theseratesareall adjustedup ordown

by onestandarddeviation(σ)andthedifferencesintheshapeof theresultant Mcol distributionsarethenusedasnuisance

param-eters in the fit. In the H→μτh channel the τ misidentification

rate fτ isfoundtobeapproximatelyflatinpTand η.Toestimate

the systematic uncertainty the pT distribution of fτ is fit with

a linear function and the rate recomputed fromthe fitted slope andintercept.ThemodifiedMcoldistributionthatresultsfromthe

recomputed background is then used to evaluate the systematic uncertainty.

CMS Collaboration / Physics Letters B 749 (2015) 337–362 343

Fig. 3. DistributionsofthecollinearmassMcolafterfittingforsignalandbackgroundfortheLFVH→μτcandidatesinthedifferentchannelsandcategoriescomparedto data.ThedistributionofthesimulatedLFVHiggsbosonsampleisshownforthebestfitbranchingfractionofB(H→μτ)=0.84%.Thebottompanelineachplotshows thefractionaldifferencebetweentheobserveddataandthefittedbackground.Topleft:H→μτe0-jet;topright:H→μτh0-jet;middleleft:H→μτe1-jet;middleright: H→μτh1-jet;bottomleft:H→μτe2-jet;bottomrightH→μτh2-jet.

Table 6

Eventyieldsinthesignalregion,100<Mcol<150 GeV afterfittingforsignalandbackground.Theexpectedcontributionsarenormalizedtoanintegratedluminosityof 19.7 fb−1.TheLFVHiggsbosonsignalistheexpectedyieldforB(H→μτ)=0.84% withtheSMHiggsbosoncrosssection.

Sample H→μτh H→μτe

0-Jet 1-Jet 2-Jet 0-Jet 1-Jet 2-Jet

Misidentified leptons 1770±530 377±114 1.8±1.0 42±17 16±7 1.1±0.7 Z→τ τ 187±10 59±4 0.4±0.2 65±3 39±2 1.3±0.2 ZZ,WW 46±8 15±3 0.2±0.2 41±7 22±4 0.7±0.2 Wγ – – – 2±2 2±2 – Z→ee orμμ 110±23 20±7 0.1±0.1 1.6±0.7 1.8±0.8 – tt 2.2±0.6 24±3 0.9±0.5 4.8±0.7 30±3 1.8±0.4 tt 2.2±1.1 13±3 0.5±0.5 1.9±0.2 6.8±0.8 0.2±0.1 SM H background 7.1±1.3 5.3±0.8 1.6±0.5 1.9±0.3 1.6±0.2 0.6±0.1 Sum of backgrounds 2125±530 513±114 5.4±1.4 160±19 118±9 5.6±0.9

LFV Higgs boson signal 66±18 30±8 2.9±1.1 23±6 13±3 1.2±0.3

Data 2147 511 10 180 128 6

7. Results

The Mcol distributions after the fit for signal and background

contributionsareshownin Fig. 3andtheeventyieldsinthemass range 100 <Mcol<150 GeV are shown in Table 6. The

differ-entchannels andcategoriesare combinedto seta 95% CL upper limitonthebranchingfractionofLFVH decayinthe μτ channel, B(H→μτ).

Theobservedandthemedianexpected95% CLupperlimitson the B(H→μτ)fortheH massat125 GeV aregivenforeach cat-egory inTable 7.Combining all the channels, an expected upper limit of B(H→μτ) < (0.75±0.38)% is obtained. The observed upper limit is B(H→μτ) <1.51% which isabove the expected limit due to an excess of the observed number of events above the background prediction.The fit can then be used to estimate the branching fraction ifthis excess were to be interpreted asa signal. The best fit values for the branching fractions are given in Table 7. The limits and best fit branching fractions are also summarized graphically in Fig. 4. The combined categories give a best fit of B(H→μτ) = (0.84₋+0₀._.39₃₇)%. The combinedexcess is 2.4standard deviations which corresponds to a p-valueof 0.010 at MH=125 GeV.The observed andexpected Mcol distributions

combinedforallchannelsandcategoriesareshownin Fig. 5.The distributions are weighted in each channel and category by the S/(S+B)ratio,whereSandBarerespectivelythesignaland back-ground yields corresponding to the result of the global fit. The valuesforS andBare obtainedinthe 100 <Mcol<150 GeV

re-gion.

8. Limitsonlepton-flavour-violatingcouplings

The constrainton B(H→μτ) can be interpreted in terms of LFVYukawacouplings [4]. TheLFV decaysH→eμ, eτ, μτ arise at treelevel from the assumed flavour-violating Yukawa interac-tions, Y_α_β where α, β denotetheleptons, α, β=e, μ, τ and

α= β_{.The decay width (H→ }α_β_{) in terms of the Yukawa} couplingsisgivenby:

(H→ αβ)=mH 8π  |Y_β_α|2+ |Y_α_β|2  , andthebranchingfractionby:

B(H→ αβ)= (H→ 

α_β₎

(H→ α_β₎₊ S M

.

TheSM H decay widthisassumedtobe SM=4.1 MeV[66] for

MH=125 GeV.The95%CLconstraintontheYukawacouplings

de-Table 7

Theexpectedupperlimits,observedupperlimitsandbestfitvaluesforthe branch-ingfractionsfordifferentjetcategoriesfortheH→μτprocess.Theone standard-deviationprobabilityintervalsaroundtheexpectedlimitsareshowninparentheses.

0-Jet (%) 1-Jet (%) 2-Jet (%) Expected Limits μτe <1.32 (±0.67) <1.66 (±0.85) <3.77 (±1.92) μτh <2.34 (±1.19) <2.07 (±1.06) <2.31 (±1.18) μτ <0.75 (±0.38 ) Observed limits μτe <2.04 <2.38 <3.84 μτh <2.61 <2.22 <3.68 μτ <1.51

Best fit branching fractions

μτe 0.87+₋00..6662 0.81+ 0.85 −0.78 0.05+ 1.58 −0.97 μτh 0.41+₋11..2022 0.21+ 1.03 −1.09 1.48+ 1.16 −0.93 μτ 0.84+0.39 −0.37

rivedfrom B(H→μτ) <1.51% andtheexpressionforthe branch-ingfractionaboveis:



|Yμτ|2+ |Yτ μ|2<3.6×10−3.

Fig. 6comparesthisresulttotheconstraintsfrompreviousindirect measurements.

9. Summary

The first direct search for lepton-flavour-violating decays of a Higgs bosonto a μ–τ pair, basedon thefull 8 TeV dataset col-lected by CMSin 2012ispresented.It improvesupon previously published indirectlimits[4,26]byanorderofmagnitude. Aslight excess of events with a significance of 2.4 σ is observed, corre-sponding toa p-valueof0.010. Thebest fitbranching fractionis B(H→μτ) = (0.84₋+0_0..39₃₇)%. A constraint of B(H→μτ) <1.51% at 95% confidencelevel is set.The limit is used to constrain the Yukawacouplings,



|Yμτ|2_{+ |Yτμ|}2_<3.6×10−3_{.Itimprovesthe}

currentboundbyanorderofmagnitude.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technical andadministrativestaffs atCERNand atother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentresand

CMS Collaboration / Physics Letters B 749 (2015) 337–362 345

Fig. 4. Left: 95% CL upper limits by category for the LFV H→μτdecays. Right: best fit branching fractions by category.

Fig. 5. Left:DistributionofMcolforallcategoriescombined,witheachcategoryweightedbysignificance(S/(S+B)).Thesignificanceiscomputedfortheintegralofthe binsintherange100<Mcol<150 GeV usingB(H→μτ)=0.84%.ThesimulatedHiggssignalshownisforB(H→μτ)=0.84%.Thebottompanelshowsthefractional differencebetweentheobserveddataandthefittedbackground.Right:backgroundsubtractedMcoldistributionforallcategoriescombined.

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); AcademyofFinland,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); MSIP and NRF (Republic ofKorea); LAS (Lithuania);MOE andUM (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

Fig. 6. Constraintsontheflavour-violatingYukawacouplings,|Yμτ|and|Yτ μ|.The

blackdashedlinesarecontoursofB(H→μτ)forreference.Theexpectedlimit (redsolidline)withonesigma(green)andtwosigma(yellow)bands,andobserved limit(blacksolidline)arederivedfromthelimitonB(H→μτ)fromthepresent analysis.Theshadedregions arederived constraintsfromnullsearches for τ→

3μ (darkgreen)and τ→μγ (lightergreen).The yellowlineisthelimit from atheoreticalreinterpretationofanATLASH→τ τ search[4].Thelightblueregion indicatestheadditionalparameterspaceexcludedbyourresult.Thepurplediagonal lineisthetheoreticalnaturalnesslimitYi jYji≤mimj/v2.(Forinterpretationofthe referencestocolorinthisfigurelegend,thereaderisreferredtothewebversionof thisarticle.)

Science, cofinanced from European Union, Regional Development Fund;the CompagniadiSan Paolo(Torino); theConsorzio per la Fisica (Trieste);MIUR project20108T4XTM(Italy); the Thalisand Aristeia programmes cofinanced by EU-ESF andthe Greek NSRF; andtheNationalPrioritiesResearchProgrambyQatarNational Re-searchFund.

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CMSCollaboration

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

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam, T. Bergauer, M. Dragicevic,J. Erö,M. Friedl, R. Frühwirth1,V.M. Ghete, C. Hartl, N. Hörmann, J. Hrubec, M. Jeitler1,W. Kiesenhofer, V. Knünz,M. Krammer1, I. Krätschmer,D. Liko, I. Mikulec, D. Rabady2,B. Rahbaran, H. Rohringer, R. Schöfbeck, J. Strauss, W. Treberer-Treberspurg,

W. Waltenberger, C.-E. Wulz1

InstitutfürHochenergiephysikderOeAW,Wien,Austria

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

NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus

S. Alderweireldt, S. Bansal,T. Cornelis,E.A. De Wolf, X. Janssen,A. Knutsson, J. Lauwers, S. Luyckx, S. Ochesanu,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, J. Keaveney,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, A. Randle-conde,T. Reis,T. Seva, L. Thomas, C. Vander Velde, P. Vanlaer, J. Wang, F. Zenoni

UniversitéLibredeBruxelles,Bruxelles,Belgium

V. Adler,K. Beernaert, L. Benucci, A. Cimmino,S. Costantini, S. Crucy, A. Fagot,G. Garcia, J. Mccartin, A.A. Ocampo Rios, D. Poyraz,D. Ryckbosch, S. Salva Diblen, M. Sigamani,N. Strobbe, 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, A. Jafari, P. Jez,M. Komm, V. Lemaitre, C. Nuttens, D. Pagano,L. Perrini, 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

W.L. Aldá Júnior, G.A. Alves,L. Brito, M. Correa Martins Junior,T. Dos Reis Martins, J. Molina, C. Mora Herrera,M.E. Pol, P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

W. Carvalho,J. Chinellato6,A. Custódio, E.M. Da Costa, D. De Jesus Damiao, C. De Oliveira Martins, S. Fonseca De Souza, H. Malbouisson, 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, S. Dograa,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, V. Genchev2,R. Hadjiiska, P. Iaydjiev,A. Marinov, S. Piperov, M. Rodozov,S. Stoykova, G. Sultanov,M. Vutova

InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria

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

UniversityofSofia,Sofia,Bulgaria

J.G. Bian, G.M. Chen,H.S. Chen, M. Chen, T. Cheng, R. Du,C.H. Jiang, R. Plestina7,F. Romeo,J. Tao, Z. Wang

InstituteofHighEnergyPhysics,Beijing,China

C. Asawatangtrakuldee, Y. Ban, S. Liu,Y. Mao, S.J. Qian, D. Wang,Z. Xu, F. Zhang8,L. Zhang, W. Zou

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

CMS Collaboration / Physics Letters B 749 (2015) 337–362 349

UniversidaddeLosAndes,Bogota,Colombia

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

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

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

InstituteRudjerBoskovic,Zagreb,Croatia

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

UniversityofCyprus,Nicosia,Cyprus

M. Bodlak,M. Finger,M. Finger Jr.9

CharlesUniversity,Prague,CzechRepublic

Y. Assran10,A. Ellithi Kamel11,M.A. Mahmoud12,A. Radi13,14

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

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

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,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

J. Talvitie,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,J. Rander, A. Rosowsky, M. Titov

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

S. Baffioni, F. Beaudette, P. Busson, E. Chapon, C. Charlot, T. Dahms,L. Dobrzynski, N. Filipovic, A. Florent, R. Granier de Cassagnac,L. Mastrolorenzo, P. Miné, I.N. Naranjo, M. Nguyen, C. Ochando, G. Ortona, P. Paganini,S. Regnard, R. Salerno,J.B. Sauvan, Y. Sirois, C. Veelken, Y. Yilmaz,A. Zabi

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

J.-L. Agram15,J. Andrea, A. Aubin,D. Bloch, J.-M. Brom,E.C. Chabert, C. Collard,E. Conte15, J.-C. Fontaine15,D. Gelé, U. Goerlach,C. Goetzmann, A.-C. Le Bihan, K. Skovpen, P. Van Hove

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

S. Gadrat

S. Beauceron,N. Beaupere, C. Bernet7,G. Boudoul2, E. Bouvier, S. Brochet, C.A. Carrillo Montoya, J. Chasserat, R. Chierici,D. Contardo2,B. Courbon, P. Depasse, H. El Mamouni, J. Fan, J. Fay, S. Gascon, M. Gouzevitch, B. Ille, T. Kurca, M. Lethuillier, L. Mirabito,A.L. Pequegnot, 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

L. Rurua

E.AndronikashviliInstituteofPhysics,AcademyofScience,Tbilisi,Georgia

C. Autermann, S. Beranek,M. Bontenackels, M. Edelhoff,L. Feld, A. Heister, K. Klein,M. Lipinski, A. Ostapchuk, M. Preuten,F. Raupach, J. Sammet, S. Schael, J.F. Schulte, H. Weber, B. Wittmer, V. Zhukov5

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

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

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,A. Künsken, J. Lingemann2, A. Nowack,I.M. Nugent,C. Pistone, O. Pooth,A. Stahl

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin,I. Asin, N. Bartosik, J. Behr, U. Behrens,A.J. Bell, A. Bethani, K. Borras, A. Burgmeier, A. Cakir,L. Calligaris, A. Campbell, S. Choudhury, F. Costanza, C. Diez Pardos,G. Dolinska, S. Dooling, T. Dorland,G. Eckerlin, D. Eckstein, T. Eichhorn, G. Flucke, J. Garay Garcia, A. Geiser, A. Gizhko, P. Gunnellini, J. Hauk, M. Hempel16, H. Jung,A. Kalogeropoulos, O. Karacheban16, M. Kasemann, P. Katsas, J. Kieseler, C. Kleinwort,I. Korol, D. Krücker, W. Lange, J. Leonard,K. Lipka,A. Lobanov, W. Lohmann16, B. Lutz,R. Mankel, I. Marfin16, I.-A. Melzer-Pellmann,A.B. Meyer, G. Mittag, J. Mnich, A. Mussgiller, S. Naumann-Emme,A. Nayak, E. Ntomari,H. Perrey,D. Pitzl, R. Placakyte, A. Raspereza, P.M. Ribeiro Cipriano, B. Roland,E. Ron, M.Ö. Sahin, J. Salfeld-Nebgen,P. Saxena, T. Schoerner-Sadenius, M. Schröder, C. Seitz,S. Spannagel, A.D.R. Vargas Trevino,R. Walsh, C. Wissing

DeutschesElektronen-Synchrotron,Hamburg,Germany

V. Blobel, M. Centis Vignali, A.R. Draeger,J. Erfle, E. Garutti, K. Goebel, M. Görner, J. Haller, M. Hoffmann,R.S. Höing, A. Junkes, H. Kirschenmann,R. Klanner, R. Kogler, T. Lapsien, T. Lenz,

I. Marchesini, D. Marconi,J. Ott, T. Peiffer, A. Perieanu, N. Pietsch,J. Poehlsen, T. Poehlsen, D. Rathjens, C. Sander, H. Schettler,P. Schleper, E. Schlieckau,A. Schmidt, M. Seidel, V. Sola, H. Stadie,G. Steinbrück, D. Troendle,E. Usai, L. Vanelderen,A. Vanhoefer

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. Frensch, M. Giffels,A. Gilbert,F. Hartmann2, T. Hauth,U. Husemann, I. Katkov5,

A. Kornmayer2, P. Lobelle Pardo, M.U. Mozer, T. Müller,Th. Müller, A. Nürnberg, G. Quast, K. Rabbertz, 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

CMS Collaboration / Physics Letters B 749 (2015) 337–362 351

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

UniversityofAthens,Athens,Greece

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

UniversityofIoánnina,Ioánnina,Greece

G. Bencze,C. Hajdu, P. Hidas,D. Horvath17, F. Sikler,V. Veszpremi, G. Vesztergombi18, A.J. Zsigmond

WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni,S. Czellar, J. Karancsi19,J. Molnar, J. Palinkas, Z. Szillasi

InstituteofNuclearResearchATOMKI,Debrecen,Hungary

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

UniversityofDebrecen,Debrecen,Hungary

S.K. Swain

NationalInstituteofScienceEducationandResearch,Bhubaneswar,India

S.B. Beri,V. Bhatnagar, R. Gupta, U. Bhawandeep, A.K. Kalsi,M. Kaur, R. Kumar,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, V. Kumar, A.K. Mohanty2, L.M. Pant, P. Shukla,A. Topkar

BhabhaAtomicResearchCentre,Mumbai,India

T. Aziz,S. Banerjee, S. Bhowmik20, R.M. Chatterjee, R.K. Dewanjee,S. Dugad, S. Ganguly, S. Ghosh, M. Guchait,A. Gurtu21, G. Kole, S. Kumar, M. Maity20,G. Majumder, K. Mazumdar, G.B. Mohanty, B. Parida,K. Sudhakar, N. Wickramage22

TataInstituteofFundamentalResearch,Mumbai,India

S. Sharma

IndianInstituteofScienceEducationandResearch(IISER),Pune,India

H. Bakhshiansohi,H. Behnamian,S.M. Etesami23, A. Fahim24, R. Goldouzian, M. Khakzad,

M. Mohammadi Najafabadi,M. Naseri, S. Paktinat Mehdiabadi, F. Rezaei Hosseinabadi, B. Safarzadeh25, M. Zeinali

InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran

M. Felcini,M. Grunewald

M. Abbresciaa,b, C. Calabriaa,b,S.S. Chhibraa,b, A. Colaleoa, D. Creanzaa,c,L. Cristellaa,b,

N. De Filippisa,c, M. De Palmaa,b,L. Fiorea,G. Iasellia,c,G. Maggia,c,M. Maggia, S. Mya,c, S. Nuzzoa,b, A. Pompilia,b,G. Pugliesea,c,R. Radognaa,b,2, G. Selvaggia,b, A. Sharmaa, L. Silvestrisa,2, R. Vendittia,b, P. Verwilligena

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

G. Abbiendia,A.C. Benvenutia,D. Bonacorsia,b, S. Braibant-Giacomellia,b, L. Brigliadoria,b, R. Campaninia,b, P. Capiluppia,b,A. Castroa,b,F.R. Cavalloa, G. Codispotia,b, M. Cuffiania,b,

G.M. Dallavallea,F. Fabbria, A. Fanfania,b, D. Fasanellaa,b,P. Giacomellia,C. Grandia,L. Guiduccia,b, S. Marcellinia, G. Masettia, A. Montanaria, F.L. Navarriaa,b,A. Perrottaa, A.M. Rossia,b,T. Rovellia,b, G.P. Sirolia,b,N. Tosia,b, R. Travaglinia,b

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

S. Albergoa,b,G. Cappelloa, M. Chiorbolia,b, S. Costaa,b, F. Giordanoa,2,R. Potenzaa,b, A. Tricomia,b, C. Tuvea,b

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

G. Barbaglia, V. Ciullia,b,C. Civininia, R. D’Alessandroa,b,E. Focardia,b,E. Galloa,S. Gonzia,b,V. Goria,b, P. Lenzia,b,M. Meschinia,S. Paolettia, G. Sguazzonia,A. Tropianoa,b

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

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

INFNLaboratoriNazionalidiFrascati,Frascati,Italy

R. Ferrettia,b, F. Ferroa, M. Lo Veterea,b, E. Robuttia,S. Tosia,b

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

M.E. Dinardoa,b,S. Fiorendia,b, S. Gennaia,2,R. Gerosaa,b,2,A. Ghezzia,b,P. Govonia,b,M.T. Lucchinia,b,2, S. Malvezzia, R.A. Manzonia,b,A. Martellia,b,B. Marzocchia,b,2,D. Menascea,L. Moronia,

M. Paganonia,b,D. Pedrinia,S. Ragazzia,b, N. Redaellia,T. Tabarelli de Fatisa,b

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

S. Buontempoa, N. Cavalloa,c, S. Di Guidaa,d,2, F. Fabozzia,c,A.O.M. Iorioa,b,L. Listaa, S. Meolaa,d,2, M. Merolaa, P. Paoluccia,2

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

P. Azzia,N. Bacchettaa,D. Biselloa,b,A. Brancaa,b,R. Carlina,b, P. Checchiaa,M. Dall’Ossoa,b,T. Dorigoa, U. Dossellia,F. Gasparinia,b,U. Gasparinia,b,A. Gozzelinoa,K. Kanishcheva,c, S. Lacapraraa,

M. Margonia,b,A.T. Meneguzzoa,b, J. Pazzinia,b, N. Pozzobona,b, P. Ronchesea,b,F. Simonettoa,b, E. Torassaa,M. Tosia,b,P. Zottoa,b,A. Zucchettaa,b,G. Zumerlea,b

a_{INFNSezionediPadova,Trento,Italy} b_{UniversitàdiPadova,Trento,Italy}

c_{Padova,Italy,UniversitàdiTrento,Trento,Italy}