Search for exotic decays of a Higgs boson into undetectable particles and one or more photons

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

exotic

decays

of

a

Higgs

boson

into

undetectable

particles

and

one

or

more

photons

.

CMS

Collaboration



CERN,Switzerland

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received1July2015

Receivedinrevisedform2December2015 Accepted7December2015

Availableonline11December2015 Editor:M.Doser

Keywords:

CMS Physics Higgs

A searchis presented for exotic decaysof aHiggsbosoninto undetectable particlesand one ortwo

isolatedphotonsinppcollisionsatacenter-of-massenergyof8 TeV.Thedatacorrespondtoan

inte-gratedluminosityofupto19.4 fb−1_{collectedwiththeCMSdetectorattheLHC.Higgsbosonsproduced}

ingluon–gluonfusionand inassociationwith aZbosonare investigated,usingmodels inwhichthe

Higgsbosondecaysintoagravitinoand aneutralinoorapairofneutralinos,followedbythedecayof

theneutralinotoagravitinoandaphoton.Theselectedeventsareconsistentwiththebackground-only

hypothesis,andlimitsare placedontheproductofcrosssectionsand branchingfractions.Assuminga

standardmodel Higgsbosonproductioncrosssection, a95%confidencelevelupper limitissetonthe

branchingfractionofa125 GeVHiggsbosondecayingintoundetectableparticlesand oneortwo

iso-latedphotonsasafunctionoftheneutralinomass.Forthisclassofmodelsandneutralinomassesfrom

1to120 GeVanupperlimitintherangeof7to13%isobtained.Furtherresultsaregivenasafunction oftheneutralinolifetime,andalsoforarangeofHiggsbosonmasses.

©2015CERNforthebenefitoftheCMSCollaboration.PublishedbyElsevierB.V.Thisisanopenaccess

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

1. Introduction

ThedetailedstudiesofthepropertiesoftheobservedHiggs bo-son[1–3]arekeycomponentsoftheLHCphysics program.Inthe standardmodel(SM) andfora givenmassoftheHiggsboson,all properties of the Higgs boson are predicted. Physics beyond the SM (BSM) mightlead to deviations fromthese predictions. Thus far,measurementsoftheHiggsbosons couplingstofermions and bosonsandofthetensorstructureoftheHiggsbosoninteraction withelectroweakgaugebosonsshownosignificantdeviations

[4,5]

withrespecttoSMexpectations.

MeasurementsofHiggsboson couplings performedforvisible decay modesprovide constraints on partial decay widths of the Higgsboson toBSMparticles. Assumingthatthecouplingsofthe Higgsboson toW and Z bosonsare smallerthan the SM values, thisindirectmethodprovidesanupperlimitonthebranching frac-tionofthe125 GeVHiggsbosontoBSMparticlesof57%ata95% confidencelevel (CL) [4,6].An explicit search forBSM Higgs bo-sondecayspresentsanalternativeopportunityforthediscoveryof BSMphysics.Theobservationofasizabledecaybranchingfraction oftheHiggsbosontoundetected(e.g.invisibleorlargelyinvisible)

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

finalstateswouldbeaclearsignofBSMphysicsandcouldprovide awindowondarkmatter[7–10].

SeveralBSMmodelspredictHiggsbosondecaystoundetectable particlesandphotons. Incertainlow-scalesupersymmetry (SUSY) models, the Higgs bosons are allowed to decay into a gravitino (



G) and a neutralino (

χ



0

1) or a pair of neutralinos [11,12]. The neutralinothen decaysintoaphoton andagravitino,thelightest supersymmetric particleanddark matter candidate.Fig. 1shows Feynman diagrams forsuch decaychains of theHiggs boson(H) produced bygluon–gluon fusion (ggH)orinassociation witha Z bosondecayingtochargedleptons(ZH).

Asthegravitinointhesemodelshasanegligiblemass[11,12], the remaining parameteris theneutralino mass.If its massis in therangemH

/

2

<

m_χ0

1

<

mH,withmH

=

125 GeV themassofthe observedHiggsboson,thebranchingfraction

B(

H

→ 

χ

0

1



G

→

γ



G



G

)

can be large. For m_χ0

1

<

mH

/

2, the decay H

→ 

χ

0 1



χ

0

1

→

γ γ



G



G is expected to dominate. The samediscussion can be applied to heavyneutralHiggsbosonswithmasseslargerthan125 GeV.The lifetimeoftheneutralinocanbefiniteinsomeclassesofBSM sce-narios,leadingtotheproductionofoneormorephotonsdisplaced fromtheprimaryinteraction.

In the SM, the signature equivalent to the signal arises when theHiggsbosondecaysasH

→

Z

γ

→

ν

νγ

¯

withabranching

frac-http://dx.doi.org/10.1016/j.physletb.2015.12.017

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

Fig. 1. Feynman diagrams for the H→undetectable+γfinal state produced via ggH (left) and ZH (right). tionof3

×

10−4.ThedecayH

→

Z

γ

hasbeenstudiedinZ

→

e+e−

and Z

→

μ

+

μ

− final states.Upper limits on the product of the crosssectionandbranchingfractionofaboutafactoroftenlarger thantheSMexpectationhavebeensetatthe95% CL[13,14].With theavailabledataset thesearchpresentedisnot sensitivetothis decay,butitissensitivetoenhancements intheHiggsboson de-cayrates toundetectable particlesandphotonsarising fromBSM physics.

Variousbackgroundprocessesleadtothesignalsignaturesand areestimatedfromsimulationorfromcontrolsamplesindata.The dominantbackgroundprocessesare from

γ

+

jets eventsand di-bosoneventsintheggH andZH search,respectively.Detailsofthe backgroundestimationtechniquesarediscussedinSection 5.The strengthofthe ZH channelanalysisisan almostbackground-free selection leading to a larger sensitivity in the model-dependent interpretation. While both the ggH andthe ZH channels provide sensitivitytoBSMHiggsbosonsignatures,theggH channelallows amodel-independentinterpretationoftheresults.

Thisanalysispresents a firstsearch for decaysofa scalar bo-sontoundetectableparticlesandoneortwoisolatedphotons.The scalar boson is produced in ggH or in ZH. The data used corre-spondto an integratedluminosity ofup to 19

.

4

±

0

.

5 fb−1 ata center-of-massenergy of

√

s

=

8 TeV in 2012 collected withthe CMSdetectorattheCERNLHC.

Theresultsofthesearcharepresentedintermsofthelow-scale SUSYbreakingmodelformH

=

125 GeV andm_χ0

1 between1 GeV and120 GeV,andformH between125 GeV and 400 GeV forthe examplecasewherem_χ0

1

=

mH

−

30 GeV.Theeffectofafinite

χ



0 1 lifetime(

τ

_χ0

1)isstudiedfortheexamplecasewheremH

=

125 GeV andm_χ0

1

=

95 GeV.

2. The CMS experiment

TheCMSdetector,definitionsofangularandspatialcoordinates, and its performance can be found in Ref. [15]. The central fea-tureofthe CMSapparatusisa superconducting solenoid, of6 m internal diameter, providing a magnetic field of 3.8 T. The field volumecontainsasiliconpixelandstriptracker,acrystal electro-magnetic calorimeter(ECAL), anda brass and scintillator hadron calorimeter.Muonsare measured in gas-ionizationdetectors em-beddedinthesteelflux-returnyokeofthemagnet. Thefirstlevel oftheCMStriggersystem,composedofspecializedhardware pro-cessors, is designedto selectthe mostinteresting events within 3 μs,usinginformationfromthecalorimetersandmuondetectors. Ahigh-level triggerprocessorfarmisusedtoreducetheratetoa fewhundredeventspersecondbeforedatastorage.

Aparticle-flowalgorithm[16,17]isusedto reconstructall ob-servableparticlesintheevent.Thealgorithmcombinesall subde-tector informationto reconstructindividual particlesand identify

them ascharged hadrons, neutral hadrons, photons, andleptons. The missingtransverse energyvector



Emiss

T is definedasthe neg-ative vector sumof the transverse momenta ofall reconstructed particles(chargedorneutral)intheevent,withEmiss_T

= |

Emiss_T

|

.Jets are reconstructedusingtheanti-kT clustering algorithm[18]with a distance parameter of R

=

0

.

5, as implemented in the FastJet package [19,20]. A multivariate selection is applied to separate jetsfromthe primary interactionandthose reconstructed dueto energydeposits associatedwithpileup interactions [21].The dis-crimination is based on thedifferences inthe jet shapes, on the relative multiplicity of charged and neutral components, and on thedifferentfractionoftransversemomentumwhichiscarriedby the hardest components. Photon identification requirements and other procedures used in selecting events can be found in Sec-tion4.

3. Data and simulation events

In the search for Higgs bosons produced in ggH, the trigger system requiresthe presenceof onehigh transverseenergy (Eγ_T) photon candidateandsignificant Emiss_T .Thepresence ofa photon candidate with E_Tγ

>

30 GeV is required within the ECAL barrel region (

|

η

γ

_{| <}

₁

_.

_{44). At thetrigger level E}miss

T is calculatedfrom calorimeter information, and is not corrected for muons. A se-lection requirement of Emiss

T

>

25 GeV is applied. The efficiency of the trigger ismonitored and measured withtwo control trig-gers for the photon andthe Emiss_T trigger requirement. The data recordedwiththistriggercorrespond toan integratedluminosity of7

.

4 fb−1 andwerepartoftheCMS“dataparking”program im-plemented forthe last partof the data takingat

√

s

=

8 TeV in 2012. Inthat program,CMSrecordedadditionaldatawithrelaxed triggerrequirements,planningforadelayedofflinereconstruction in2013afterthecompletionoftheLHCRun 1.

For the search for Higgs bosons produced in ZH, collision eventswere collected usingsingle-electronandsingle-muon trig-gers whichrequirethepresence ofan isolated leptonwith pT in excessof27 GeV and24 GeV,respectively.Alsoadileptontrigger wasused,requiringtwoleptonswithpTthresholdsof17 GeV and 8 GeV.Theluminosityintegratedwiththesetriggersat

√

s

=

8 TeV is19

.

4 fb−1.

Several MonteCarlo (MC) eventgenerators are used to simu-late signal and backgroundprocesses. Thesimulated samplesare usedtooptimizetheeventselection,evaluateselectionefficiencies andsystematicuncertainties, andcompute expectedeventyields. In all casesthe MC samplesare reweighted to matchthe trigger efficiencymeasuredindata.

The V

γ

, WZ, ZZ, VVV (where V represents W or Z bosons), Drell–Yan(DY) productionof qq

¯

→

Z

/

γ

∗,andqq

¯

→

W+W− pro-cessesare generatedwiththe MadGraph 5.1eventgenerator[22]

atleading-order(LO), thegg

→

W+W− processisgeneratedwith theLO eventgenerator gg2ww 3.1 [23], andthe t

¯

t and tW pro-cesses are generated with powheg 1.0 at next-to-leading-order (NLO).Thesignal samplesarealsoproducedwith MadGraph.The crosssectionsatNLO orhigher ordersif availableare used fora given process to renormalize the MC event generators. All pro-cesses are interfaced to the pythia 6.4 generator [24] for parton showerandhadronization.

The CTEQ6L set of parton distribution functions(PDF) [25] is used forLO generators, while the CT10 [26] PDF set is used for NLO generators. Forall processes,the detector responseis simu-latedwithadetaileddescriptionoftheCMSdetector,basedonthe Geant_{4 package [27]. Additional pp interactions overlapping the} eventofinterestindata,denotedaspileupevents,areaccounted forby simulating pp interactions with the pythia generator and addingthemtoeachMCsample.TheMCsamplesaretunedto re-producethe distribution inthe numberof pileupevents indata. Theaveragenumberofpileupeventsisabout26forthecollected dataused in the ggH channel, and is about21 for the collected datausedintheZH channel.

4. Event selection

Twostrategies are followedto isolate the Higgsboson events producedby ggH andby ZH fromthe backgroundprocesses.The signalcrosssectionsareseveralordersofmagnitudesmallerthan themajorreduciblebackgroundprocesses,whosecontributionsare greatlyreducedusingtheeventselectionsdescribedinthe follow-ingsub-sections.

4.1.EventselectionintheggH channel

IntheggH channel, eachselectedeventisrequiredto haveat leastonephotoncandidatewithEγ_T

>

45 GeV and

|

η

γ

| <

1

.

44 us-ing a cut-based selection [28,29].To reduce the SM backgrounds arisingfromtheleptonic decaysofW andZ bosons,aleptonveto isapplied.Eventsare rejectedifthey haveone ormoreelectrons fulfillinga looseidentificationrequirement[30] and pe_T

>

10 GeV and

|

η

e

_{| <}

₂

_.

_{5,excludingthetransitionregionof1}

_.

₄₄

_<

_|

_η

e

_{| ≤}

₁

_.

₅₇ since the reconstruction of an electron object in this region is not optimal. Similarly, events containing muon candidates with

pμ_T

>

10 GeV,

|

η

μ

| <

2

.

1,andwellseparatedfromthephoton can-didaterequiring



R

(

γ

,

μ

)

=



(

η

)

2

_{+ (φ)}

2

_>

₀

_.

_{3 (wherethe}

_φ

isazimuthalangleinradians),arerejected. Inadditiontothe se-lectionrequirementsdescribed above, the Emiss

T is requiredto be greater than 40 GeV. Thislevel of selection is referred to asthe preselection.Additionalselectioncriteriaareappliedtosearchfor new physics in either a quasi model-independent way or opti-mizedforaSUSYbenchmarkmodel.Inthischanneljetscanarise frominitial-stateradiation.Forboth search strategiesjetsare re-quiredto have p_Tj

>

30 GeV and

|

η

j

_{| <}

₂

_.

_{4. These jetsmust not}

overlapwiththephotoncandidatebelow



R

(

γ

,

jet

)

<

0

.

5. In the model-independent analysis, events with two or more jetsare rejected.Foreventswithonejet theazimuthal angle be-tweenthephotonandthejet(

φ (

γ

,

jet

)

)isrequiredtobesmaller than 2.5.Thisselectionrequirementrejects thedominant

γ

+

jet background,wherethephotonandthejettendtobeback-to-back inthetransverseplane.

Inthemodel-dependentanalysisdevelopedforSUSYscenarios, no requirement is applied on jet multiplicity. In order to mini-mizethecontributionfromprocessessuchas

γ

+

jets andmultijet events,twomethodsareusedforidentifyingeventswith mismea-sured Emiss_T .The Emiss_T significance method[31] takesaccount of reconstructedobjects foreacheventandtheir known resolutions tocompute an event-by-eventestimate ofthelikelihoodthat the

observed Emiss_T isconsistentwithzero.Inaddition,aminimization method[29]constructsa

χ

2_{functionoftheform}

χ

2

₌



i=objects



(

pTreco

)

i

− (

pT

)

i

(

σ

pT

)

i



2

+





Emiss_x

σ

_Emiss x



2

+



_

Emiss y

σ

_Emiss y



2

,

(1)

where

(

pTreco

)

i are thescalar transverse momenta of the

recon-structed objects, such as jets and photons that pass the above-mentioned identification criteria,the

(

σ

pT

)

i are theexpected res-olutionsineachobject,the

σ

_Emiss

x,y are theresolutions ofthe E miss T projection along the x-axisandthe y-axis, andthe

(



pT

)

i are the

free parameters allowed to vary in the minimization of the

χ

2 function.The



Emiss_x,y termsarefunctionsofthefreeparameters



px,y,



Emiss_x,y

=

Emiss_x,y ,reco

+



i=objects

(

preco_x,y

)

i

− (

px,y

)

i

.

(2)

In events with no genuine Emiss

T , the mismeasured quantities arere-distributedbackintotheparticlemomenta tominimizethe

χ

2 _{value.EventsarerejectediftheminimizedE}miss

T (



E miss T )isless than45 GeV andthechi-squareprobabilityislargerthan10−3_.

Tofurther suppressmultijet backgrounds,events are not con-sideredifthescalarsumofthetransversemomentaofthe identi-fiedjetsintheevent(HT) isgreaterthan100 GeV. Anadditional requirementisapplied ontheangle(

α

)betweenthebeam direc-tionandthemajoraxisofthesupercluster[28] inorderto reject non-promptphotonsthathaveshowerselongatedalongthebeam line.

Finally,thetransversemass,

mγE

miss T

T

≡

2Eγ_TEmiss_T

[

1

−

cos

φ (

γ

,

Emiss_T

)

],

formedbythephotoncandidate,



Emiss_T ,andtheiropeningangle,is requiredtobegreaterthan100 GeV.Photonsfromthecontinuum Z

γ

backgroundhaveaharderspectrumthanthephotonsresulting fromtheHiggsdecayintheSUSY benchmarkmodelsconsidered. Tofurther reduce the continuum Z

γ

background andformodels withmH

=

125 GeV a cut of EγT

<

60 GeV isapplied. Forhigher massesthe cut is optimizeddepending oneach mass hypothesis goingfrom60 GeV upto200 GeV formH

=

400 GeV.

Thelistofselectioncriteriausedinthemodel-independent and theSUSYbenchmarkmodelanalysesaregivenin

Table 1

,together withthecumulativeefficienciesrelativetothepreselectionfor sig-nalandbackgroundprocesses.

4.2. EventselectionintheZH channel

TheleptonicdecaysoftheZ boson,consistingoftwooppositely charged same-flavor high-pT isolated leptons (e+e−,

μ

+

μ

−), are usedtotagtheHiggsbosoncandidateevents.Largemissing trans-verseenergyfromtheundetectableparticles,atleastoneisolated high-ET photon,andlittleormoderatejetactivityarerequiredto selectthesignalevents.

Thedetailsoftheleptoncandidateselectionandmissing trans-verse energy reconstruction are given in Ref. [32]. In addition, photon requirements based on a multivariate selection discussed in Refs. [28,33]have beenused. Thekinematic selection requires twoleptonswithpT

>

20 GeV andonephotonwithEγ_T

>

20 GeV. Furthermore,thedileptonmassmustbecompatiblewiththatofa Z bosonwithin15 GeV ofthepolemass.

ToreducethebackgroundfromWZ events,eventsareremoved if an additional loosely identified lepton is reconstructed with

Table 1

SummaryofggH selectionforboththequasimodel-independentanalysisandtheanalysiswiththeSUSYbenchmarkmodelwiththecumulativeefficienciesoftheselection requirementsrelativetothepreselectionforZγ→ννγ¯ ,γ+jet andforasignalinaSUSYbenchmarkmodelwithggH productionofaHiggsbosonwithmass125 GeV decayingintoaneutralinoofmass120 GeV andaphoton.

Selection requirements Model-independent SUSY benchmark model

Zγ→ννγ¯ γ+jet Zγ→ννγ¯ γ+jet m_χ0

1=120 GeV

Number of jets<2 0.909 0.769 – – –

φ(γ,jet) <2.5 radians 0.834 0.262 – – –

Transverse mass>100 GeV – – 0.867 0.292 0.829

HT<100 GeV – – 0.785 0.188 0.804 Emiss T >45 GeV – – 0.761 0.071 0.743 Prob(χ2_{) <10}−3 _{– – 0.626 0.033 0.467} ETmisssignificance>20 – – 0.440 0.001 0.195 α>1.2 – – 0.390 0.001 0.165 ETγ<60 GeV – – 0.074 0.0002 0.106 Table 2 SummaryofZH selection. Variable Selection

Leptons 2 leptons, pT>20 GeV

Photons 1 photon, EγT>20 GeV

|m−mZ| <15 GeV

Anti b-tagging applied

Jet veto 0 jets with pTj>30 GeV

φ,Emiss T +E γ T >2.7 radians |pEmissT +E γ T T −p  T|/p  T <0.50 φ <2.25 radians p T >60 GeV Emiss T >60 GeV

isrejected ifit passesthe b-taggingselection (anti b-tagging) or if there is a selected jet with pT larger than 30 GeV (jet veto). Theb-taggingselectionisbasedonthepresenceofamuoninthe eventfromthesemileptonicdecayofabottom-quark, andonthe impactparametersoftheconstituenttracksinjetscontaining de-caysofbottom-quarks[34].Thesetofb-taggingvetocriteriaretain about95%ofthelight-quarkjets,whilerejectingabout70%ofthe b-jets.

The signal topology is characterized by a Z

()

system with large transverse momentum balanced inthe transverse plane by a E



miss_T

+ 

Eγ_T systemfromthe Higgsboson decay.Toreject back-groundfromZ

γ

andZ

+

jets eventswithmisreconstructed Emiss_T

the azimuthal angle

φ

_,Emiss T +E

γ

T is required to be greater than 2.7 radians, the variable

|

pE

miss T +E γ T T

−

p  T

|/

p  T is required to be smallerthan0.5,andtheazimuthalanglebetweenthetwoleptons

φ

 isrequiredtobesmallerthan2.25radians.Finally,pT is re-quiredtobelargerthan60 GeV,andEmiss_T isrequiredtobelarger than60 GeV.Asummaryoftheselectionfortheanalysisisshown in

Table 2

.

The signal-to-background fraction depends on the

|

η

γ

_|

_{, the}

pseudorapidityofthephoton,withgreaterdiscriminationatlower values.Toexploit thiseffectandimprovesensitivity,theselected eventsare subdividedaccordingto whetherthephoton is recon-structed in the barrel or endcap regions, as explained in Sec-tion7.2.

5. Background estimation

Thebackgroundestimation techniquesandthecomposition of allbackgroundsinthesearchwiththeggH andZH signaturesare discussed below. The yield for the irreducible background from H

→

Z

γ

→

ννγ

isnegligibleandisthereforeignoredinthe anal-ysis.

5.1. BackgroundestimationintheggH channel

The dominantbackgroundforthe

γ

+

Emiss_T signalinthe ggH channel is the process

γ

+

jet. Other SM backgrounds include Z

γ

→

ν

νγ

¯

,W

γ

,W

→

e

ν

,W

→

μν

,W

→

τ ν

,multijet,and dipho-tonevents.Backgroundeventsthatdonotarisefromppcollisions arealsoconsideredintheanalysis.Thesebackgroundscanbe cat-egorizedbroadlyintothreecategories,asdescribedbelow.

5.1.1. Backgroundestimatesfromsimulation

The

γ

+

jet process surviving the various E_Tmiss selection re-quirements is one of the most significant backgrounds in this analysis due to the presence of an isolated photon andits large productioncrosssection.TheMCnormalizationofthisbackground is corrected using control samples indata for two eventclasses, events without jets and those with one or more jets. The con-trol samples in data are obtained using events collected with a prescaledsingle-photontriggerandwiththeEmiss_T requirement re-versed to ensure orthogonality to the signal phase space, where the contamination from other processes is minimal. Multiplica-tivecorrectionfactors(C )areobtainedafternormalizingtheevent yield in the simulation to match the data in the control region, separately foreventswithno jets(C

=

1

.

7)andoneormorejets (C

=

1

.

1).Thesecorrectionfactorsare usedtonormalizethe sim-ulated

γ

+

jet event yieldin thesignal region.An uncertaintyof 16% is obtainedfor these correction factors based on the differ-ence between the corrected anduncorrected simulation and the relative fractionof nojet events (about10% ofthe eventsin the control region)andone ormorejet events.The background pro-cessesZ

γ

→ 

γ

andW

→

μν

contributeonlyasmallfractionof thetotalbackgroundprediction,duetotheleptonvetoappliedat thepreselectionstage,andaremodeledusingsimulatedsamples.

To take intoaccount differences betweendata andsimulation due toimperfect MC modeling,various scale factors (SF) are ap-plied tocorrectthe estimatesfromsimulation.These SFsare de-fined by the ratio of the efficiency in data to the efficiency in simulationforagivenselection.The SFforphotonreconstruction andidentificationisestimatedfromZ

→

e+e− decays[35]andis consistentwithunity.

5.1.2. Backgroundestimatesfromdata

Thecontaminationfromjetsmisidentifiedasphotons(jet

→

γ

) isestimatedinadatacontrolsampleenrichedwithmultijetevents definedby Emiss

T

<

40 GeV.Thissampleisusedtomeasurethe ra-tioofthenumberofcandidatesthatpassthephotonidentification criteria to those failing the isolation requirements. The numera-torofthisratioisfurthercorrectedforthephotoncontamination duetodirectphotonproductionusingan isolationsideband. The

Table 3

SummaryofallrelativesystematicuncertaintiesinpercentforthesignalandbackgroundestimatesfortheHiggsmodel(model-independentinparenthesis)selectioninthe ggH analysis.

Source Signal Jet→γ Electron→γ γ+jet Zννγ Wγ

PDF 10 (0) – – – 4 (4) 4 (4)

Integrated luminosity 2.6 (2.6) – – 2.6 (2.6) 2.6 (2.6) 2.6 (2.6)

Photon efficiency 3 (3) – – 3 (3) 3 (3) 3 (3)

Photon energy scale±1% 4 (0.5) – – 4 (0.5) 4 (0.5) 4 (0.5)

Emiss

T energy scale 4 (2) – – 4 (2) 4 (2) 4 (2)

Jet energy scale 3 (2) – – 5 (5) 3 (2) 3 (2)

Pileup 1 (1) – – 1 (1) 1 (1) 1 (1) Zννγ normalization – – – – 3 (3) – γ+jet normalization – – – 16 (16) – – Wγnormalization – – – – – 3 (3) Jet→γ – 35 (35) – – – – Electron→γ – – 6 (6) – – –

corrected ratiois applied to data eventswhich pass the denom-inator selection and all other event requirements in the signal region.

Thesystematicuncertaintyofthismethodisdominatedbythe choice of the isolation sideband, and is estimated to be 35% by changing the isolation criteria in the sideband region definition. The other sources of systematic uncertainty are determined by changingthe Emiss

T selectionforthe controlregion,andtheloose identificationrequirementsonthephotons,allofwhicharefound tobecomparativelysmall.

Events with single electrons misidentified as photons (electron

→

γ

)areanothermajorsourceofbackground.This back-groundisestimatedwithatag-and-probemethodusingZ

→

e+e− events[36].The efficiencytoidentify electrons(

γe) isestimated in the Z boson peak mass window of 60–120 GeV. The ineffi-ciency(1

−

γe)isfoundtobe2

.

31

±

0

.

03%.Theratio

(

1

−

γe

)/

γe, whichrepresentstheelectron misidentificationrate,is appliedto asample wherecandidates are requiredtohavehitsin thepixel detector,andisused toestimate the contamination inthe signal region.Themisidentificationrateisfoundtobedependentonthe numberofverticesreconstructedintheeventandthe numberof tracksassociatedwith theselected primaryvertex. Thedifference inthefinalyieldstakingthisdependenceintoaccountor neglect-ingit,usingtheinclusivemeasurementof

γe,islessthan5%.

5.1.3. Non-collisionbackgroundestimatesfromdata

The search is susceptible to contamination from non-collision backgrounds, which arise from cosmic ray interactions, spurious signalsin the ECAL,and accelerator-induced secondary particles. The distribution of arrival-times of photons from these back-groundsisdifferentfrom thatofpromptphotonsproducedinhard scattering.Toquantifythecontaminationfromthesebackgrounds a fit isperformed to the candidate-time distribution using back-grounddistributionsfromthedata[29].Thecontaminationdueto out-of-timebackgroundcontributionsisfoundtobelessthanone percentof the total backgroundand is thereforenot included in thefinaleventyield.

5.2.BackgroundestimationinZH channel

ProcessesthatcontributesignificantlytotheSMexpectationin theZH channelarelistedbelow.

5.2.1. Non-resonantdileptonbackgrounds

The contributions from W+W−, top-quark, W

+

jets, and Z

/

γ

∗

→

τ

+

τ

− processes are estimated by exploiting the lepton flavor symmetry in the final states of these processes [37]. The branching fraction to the e±

μ

∓ final state is twice that of the e+e− or

μ

+

μ

− final states. Therefore, the e±

μ

∓ control region

isusedtoextrapolate thesebackgroundstothee+e− and

μ

+

μ

− channels. The methodconsiders differencesbetweentheelectron and muon identification efficiencies. The data driven estimates agreewellwiththenumberofbackgroundeventsexpectedwhen applying the same method to simulation. The small difference between the prediction and the obtained value using simulated eventsistakenasasystematicuncertainty.

The limitednumber ofsimulatedevents isalso considered as partofthe systematicuncertainty.Insummary,the total system-aticuncertaintyisabout75%.Onlytwoeventswereselectedinthe datacontrolregion.

5.2.2. Resonantbackgroundwiththreeleptonsinthefinalstate

The WZ

→ 

ν



process dominatesthe resonant backgrounds withthreeleptonsinthefinalstate.Theelectron

→

γ

misidentifi-cationrateismeasuredinZ

→

e+e− eventsbycomparingthe ra-tiosofelectron–electronversuselectron–photonpairsindataand insimulation,asdescribedinSection5.1.2.Theaverage misidenti-ficationrateis1–2%withthelargervaluesathigher

|

η

|

γ .

5.2.3. Resonantbackgroundwithtwoleptonsinthefinalstate

TheWZ

→ 

ν



processwithfailuretoidentifytheleptonfrom W bosondecaysandtheZZ

→

2



2

ν

processdominatethesetypes ofevents.Thejet

→

γ

misidentificationrateismeasuredina sam-plecontainingamuonandaphoton.Thissampleisexpectedtobe dominatedbyjetsmisidentifiedasphotons,withsome contamina-tion fromW

/

Z

γ

events,whichare subtracted inthe studyusing the simulated prediction. The misidentification rate is similar to theobtainedvaluesintheggH channel.

5.2.4. Resonantbackgroundwithnogenuinemissingtransverseenergy

ThebackgroundfromZ

γ

orZ

+

jets eventsispredictedbythe simulation tobe about15% ofthe totalbackground.Severaldata regionsarestudiedtoverifythatthebackgroundisestimated cor-rectly. A good agreement between data and simulation is found in all cases. A 50% uncertainty, the statisticaluncertainty of the controlregion,istakenforthesebackgroundsestimatedfrom sim-ulation.

6. Summary of systematic uncertainties

Systematicuncertaintiesinthebackgroundestimatesfrom con-trolsamplesindataaredescribedinSection5.Asummaryofthe systematic uncertainties considered in each channel are listed in

Tables 3 and 4.

Acommonsourceofsystematicuncertaintyisassociatedwith the measurement of the integrated luminosity, determined to 2.6% [38]. The uncertainties in the normalization of signal and

Table 4

SummaryofrelativesystematicuncertaintiesinpercentforthesignalandbackgroundestimatesintheZH analysis.

Source ZH Zγ or Z+jets WZ ZZ WW+top-quark

Integrated luminosity 2.6 – 2.6 2.6 – Lepton efficiency 3.6 – 3.6 3.6 – Photon efficiency 3.0 – – – – Momentum resolution 0.5 – 1 1 – Emiss T energy scale 0.5 – 0.6 0.1 –

Jet energy scale 2 – 4 4 –

b-tagging 0.7 – 0.7 0.7 –

Underlying event 3 – – – –

PDF 7.1 – 6.3 7.7 –

Renorm. and factor. scales 7.0 – 10.7 6.5 –

Z/γ∗→ +−_{normalization – 50 – – –}

Non-resonant dilepton bkg. norm. – – – – 70

Jet→γ – – 30 30 –

Electron→γ – – 10 10 –

Amount of simulated events 3.5 60 10 30 40

simulation-basedbackgrounds areobtainedby varying the renor-malization and factorization scales, and the parton distribution functions[26,39–43].

Because the model-independent and model-specific selections differ significantly in the ggH channel, the systematic uncertain-tiesareevaluatedseparatelyforeachselection.Thephotonenergy scale uncertainty [28] of about 1% affects the signal and back-groundpredictionsby 4% forthe model-specific selectionandby 0.5%forthemodel-independentselection.Similarly,thejetenergy scaleuncertaintyaffectsthesignalandbackgroundpredictionsby 2–5%depending on theprocess andselection.Afterchangingthe photonorjetenergyscales,the Emiss_T isalsorecomputed.In addi-tion,thesystematicuncertaintyassociatedwiththejetenergy res-olutionandunclusteredenergy scaleare propagated tothe Emiss_T

computation,andaffectthesignalandbackgroundpredictionsby 2–4%. As described inthe previous section, a 16% uncertaintyis appliedto the

γ

+

jet normalization duetothedifference inthe jetmultiplicitydistributionbetweenthedataandbackground pre-dictionsinthe

γ

+

jet control region.Theuncertaintyduetothe pileup modeling is found to be 1%, and is estimated by shifting thecentralvalueofthetotalinelasticcrosssectionwithin its un-certainty.

In the ZH channel, lepton-reconstruction and identification scalefactorsaremeasuredusingacontrolsampleofZ

/

γ

∗

→ 

+



−

events in the Z peak region [36]. The associated uncertainty is about2%perlepton.Thephotonidentificationuncertaintyistaken to be 3% [33]. Theeffect ofuncertainties in jet energy scale and

Emiss_T on the analysis is also considered. The uncertainty in the b-taggingefficiency is estimatedto be about 0.7% comparing in-clusive Z

/

γ

∗

→ 

+



− _{samples in data and simulation. The total}

uncertainty in the background estimates in the signal region is 36%,whichisdominatedbythestatisticaluncertaintiesinthedata controlsamplesfromwhichtheyarederived.

Theimpactofthesystematicuncertainties intheggH channel is relatively important: the sensitivity isincreased by about 50% if all the systematic uncertainties are removed, where the nor-malizationuncertainties onthe

γ

+

jet and jet

→

γ

background processes dominate. The ZH channel is limited by the statistical uncertainty,andthe effectofthe systematicuncertainties reduce thesensitivitybylessthan10%.

Correlationsbetweensystematicuncertaintiesinthetwo chan-nels are taken into account. In particular, the main sources of correlated systematicuncertainties are those inthe experimental measurements suchasthe integratedluminosity,photon identifi-cation,thejetenergyscale,andmissingtransverseenergy resolu-tion. Allother systematicuncertainties are uncorrelated between themgiventhedifferentsignalandbackgroundprocesses.

Table 5

Observedyieldsandbackgroundestimatesat8 TeV inthe ggH channelafterthemodel-independentselection. Statisti-calandsystematicuncertaintiesareshown.

Process Event yields

γ+jets (313±50)×103 jet→γ (910±320)×102 e→γ 10 350±620 W(→ ν)+γ 2239±111 Z(→νν¯)+γ 2050±102 Other 1809±91 Total background (420±82)×103 Data 442×103 7. Results

The results fromthe two searches andtheir combination are reported in this section. In the absence of deviations from the standard model predictions, the modified frequentist method, CLs[44–46],isusedtodefinetheexclusionlimits.

7.1. Model-independentresultsintheggH channel

Because ofthevarietyofpossibleBSMsignalsthatcould con-tributetothisfinalstate,theresultsarepresentedforasignalwith themodel-independentselectiondescribed inSection4.Thetotal numberofobservedeventsandtheestimatedSMbackgroundsare summarized in

Table 5

,andfound to be compatiblewithin their uncertainties.

Fig. 2

showsthemγE

miss T

T and E

miss

T distributionsfor themodel-independentselection.

Fig. 3 shows the observed and expected model-independent 95% CL upperlimitsfortheggH analysis ontheproduct ofcross section, acceptance, and efficiency for mγE

miss T

T

>

100 GeV, as a functionofEmiss_T threshold.

7.2. Model-specificresultsintheggH channel

Imposingthemodel-specificselectiondescribedinSection4for the ggH channel, 1296 events are selected in data with a total estimated background of 1232

±

188. The yields for this selec-tion are shownin Table 6andestimated forHiggsboson decays (H

→ 

G

χ



0

1

,

χ



10

→ 

G

γ

) assuming the ggH production rate forSM Higgsbosons anda 100%branching fractionforthisdecay. Fig. 4

showsthe transverseenergydistribution ofphotonsfordata,the background estimates, and signal after the model-dependent se-lection, except the upper selection on the photon, for the ggH channel.

Fig. 2. ThemγEmissT

T andE

miss

T distributionsfordata,backgroundestimates,and sig-nalafterthemodel-independentselectionfortheggH channel.Thebottompanels ineachplotshowtheratioof(data−background)/background andthegrayband includesboththe statisticalandsystematicuncertaintiesinthebackground pre-diction.ThesignalisshownformH=125 GeV andm_χ0

1 =120 GeV anda100% branchingfraction.

7.3.ResultsintheZH channelandcombinations

Atotalof foureventsare selectedwiththe searchin ZH.The background yield is estimated to 4

.

1

±

1

.

8. The numbers of ob-served and expected events are shown in Table 7. The signal model assumes a SM ZH production rate and a 100% branching fraction to undetectable particles and one or two photons. The expected signal yield is larger for cases where m_χ0

1 is smaller than mH

/

2 since there are two photons in the final state (H

→



χ

0

1



χ

10

→

γ γ



G



G), and as a result the sensitivity improves for smallermasses.Good agreementbetweenthedataandthe back-ground prediction is observed. The transverse mass, mE

miss T

T

≡

Fig. 3. Theexpectedandobserved95%CLupperlimitontheproductofcross sec-tion,acceptance,andefficiency(σ(pp→γ+EmissT )A )form

γEmiss T

T >100 GeV,as functionoftheEmiss

T thresholdfortheggH channel.

Table 6

Observedyields,backgroundestimates,andsignalpredictionsat8 TeV intheggH channelfordifferentvaluesofthem_χ0

1 andfor differentcτχ10 ofthe χ 0 1.These correspondtoB(H→undetectable+γ)=100%,assumingtheSMcrosssectionat thegivenmHhypothesis.Thecombinationofstatisticalandsystematicuncertainties isshownfortheyields.

Process Event yields

ggH(mH=125 GeV,m_χ0 1=65 GeV) 653±77 ggH(mH=125 GeV,m_χ0 1=95 GeV) 1158±137 ggH(mH=125 GeV,m_χ0 1=120 GeV) 2935±349 ggH(mH=125 GeV,mχ0 1=95 GeV)cτχ10=100 mm 983±116 ggH(mH=125 GeV,m_χ0 1=95 GeV)cτχ10=1000 mm 463±55 ggH(mH=125 GeV,m_χ0 1=95 GeV)cτχ10=10 000 mm 83±10 ggH(mH=150 GeV,m_χ0 1=120 GeV) 4160±491 ggH(mH=200 GeV,m_χ0 1=170 GeV) 5963±704 ggH(mH=300 GeV,m_χ0 1=270 GeV) 5152±608 ggH(mH=400 GeV,mχ0 1=370 GeV) 4057±479 γ+jets 179±28 jet→γ 269±94 e→γ 355±28 W(→ ν)+γ 154±15 Z(→νν¯)+γ 182±13 Other 91±10 Total background 1232±188 Data 1296

2p_T pE miss T +E γ T

T

[

1

−

cos

(φ

,Emiss_T +Eγ_T

)

]

,and

|

η

γ

|

distributions

dis-criminate signal and background andare shownin Fig. 5 at the finalstepoftheselection.

The 95% CL upper limits are extracted from counting exper-iments in three categories: the model-specific selection in the ggH channel, and photons identified in the barrel and the end-capcalorimetersfortheZH channel.Resultsarecombinedusinga binned-likelihoodmethod.The95%CLupperlimitson

(

σ

B)/

σ

SM, where

σ

SM isthecrosssection fortheSM Higgsboson,are eval-uated for different mass values of

χ



0

1 ranging from 1 GeV to 120 GeV fortheindividualsearchesandtheircombinationandare shownin

Fig. 6

.Theupperlimitsform_χ0

1

<

mH

/

2 arenotshown fortheggH channelbecausethesensitivityisverylowduetothe combinationkinematicpropertiesandthecorrespondingselection; inparticulartheEmiss

Fig. 4. Thetransverseenergydistributionofphotonsfordata,thebackground es-timates,andsignalafterthemodel-dependentselection(excepttheupper selec-tiononthe photon)for theggH channel.The bottompanel showsthe ratioof (data−background)/background andthe graybandincludesboth thestatistical andsystematicuncertaintiesinthebackgroundprediction.Thesignalisshownfor

mH=125 GeV andm_χ0

1=120 GeV.

Table 7

Observedyields,backgroundestimates,andsignalpredictionsat8 TeV intheZH channelfordifferentvaluesofthem_χ0

1 andfordifferentcτχ10 oftheχ 0 1.The sig-nalpredictionscorrespondtoB(H→undetectable+γ)=100% assumingtheSM ZH crosssectionatthegivenmHhypothesis.Thecombinationofstatisticaland sys-tematicuncertaintiesisshownfortheyields.

Process Event yields

ZH(mH=125 GeV,m_χ0 1=1 GeV) 69.2±8.4 ZH(mH=125 GeV,m_χ0 1=10 GeV) 68.6±8.4 ZH(mH=125 GeV,m_χ0 1=30 GeV) 53.5±6.5 ZH(mH=125 GeV,m_χ0 1=60 GeV) 47.7±5.8 ZH(mH=125 GeV,m_χ0 1=65 GeV) 40.0±4.9 ZH(mH=125 GeV,mχ0 1=95 GeV) 40.3±4.9 ZH(mH=125 GeV,m_χ0 1=120 GeV) 39.0±4.8 ZH(mH=125 GeV,m_χ0 1=95 GeV)cτχ10=100 mm 39.3±4.8 ZH(mH=125 GeV,m_χ0 1=95 GeV)cτχ10=1000 mm 17.6±2.2 ZH(mH=125 GeV,m_χ0 1=95 GeV)cτχ10=10 000 mm 2.6±0.3 ZH(mH=200 GeV,m_χ0 1=170 GeV) 13.1±1.6 ZH(mH=300 GeV,m_χ0 1=270 GeV) 3.5±0.4 ZH(mH=400 GeV,mχ0 1=370 GeV) 1.2±0.1 Zγ+Z+jets 0.6±0.4 WZ 1.2±0.3 ZZ 0.3±0.1 WW+top-quark 2.0±1.7 Total background 4.1±1.8 Data 4

selectedranges.A95%CLupperlimitonthebranchingfractionof 10%issetforaneutralinomassof95 GeV.

Expected andobservedlimitsare alsoshownforthedecayof possibleheavierscalarHiggsbosonsasafunctionoftheHiggs bo-sonmassin

Fig. 7

.TherequirementonE_Tγ usedintheggH channel isremoved.Alowerthresholdon Eγ_T isadded,optimizedto

max-Fig. 5. Distributionsinsignal wheremH=125 GeV andm_χ0

1=95 GeV,backgrounds anddataformEmissT

T (top)and|ηγ|(bottom)afterapplyingallrequirements.The uncertaintybandforthebackgroundsincludesbothstatisticalandsystematic un-certainties.ThesignalmodelassumesaSMZH productionrateforaHiggsboson withmH=125 GeV anda10%branchingfraction.

imize thesensitivity foreach mass hypothesis. A combination of the two channelsis not performed because the assumption of a commonSMHiggsbosoncrosssectionisnotjustified.

Asdiscussedintheintroduction,some BSMmodelspredict



χ

0 1 neutralinoswithsizablelifetimes.Theperformanceofthesearches hasbeenevaluatedforfinitelifetimeswithoutmodifyingthe anal-ysisstrategy.Theexpectedandobservedlimitsareshownin

Fig. 8

asfunctionofc

τ

_χ0

1.TheresultsareshownformH

=

125 GeV and

m_χ0

1

=

95 GeV.Asseen inTables 6 and 7,theselectionefficiency isroughly constantforvaluesofc

τ

_χ0

1 lessthan10 cm,anddrops rapidlyforlargervalues.Thedefaulttimingcriteriaappliedinthe ECAL energyreconstruction arethe causeforthedecrease inthe efficiency. In particular,there is a requirementof a maximumof 3 ns on the photon arrival time relative to thenominal time-of-flight forprompt photons.The delayedarrival time ofthe photon

Fig. 6. Expectedandobserved95%CLupperlimitsonσB/σSMformH=125 GeV asafunctionofm_χ0

1 assumingtheSMHiggsbosoncrosssections,fortheZH and ggH channelsandtheircombination,withB≡ B(H→ χ0

1χ 0 1)B(χ 0 1→ G+γ) 2_for m_χ0 1<mH/2 andB≡ B(H→ χ 0 1G)B(χ10→ G+γ)formχ0 1≥mH/2.

Fig. 7. Expectedandobserved95%CLupperlimitsonσgg→HBasafunctionofthe Higgsbosonmasswithm_χ0

1=mH−30 GeV inggH channel(top)andintheZH channel(bottom).

Fig. 8. Expectedandobserved95%CLupperlimitsonσHBasafunctionofcτχ0 1 formH=125 GeV andmχ_0

1=95 GeV,whereB≡ B(H→ χ 0 1G)B(χ

0 1→ G+γ). canbecausedbyakinkinthetrajectoryorbyalowervelocityof theneutralino.

8. Summary

A search is presentedfor exoticdecays ofa Higgs boson into undetectableparticles andoneortwoisolatedphotonsinpp col-lisions at acenter-of-mass energyof 8 TeV.The data correspond toan integratedluminosityofup to19

.

4 fb−1 collected withthe CMSdetector atthe LHC.Higgs bosons produced ingluon–gluon fusion or in association witha Z bosonare investigated.Models includingHiggsbosondecaysintoagravitinoandaneutralino or a pairofneutralinos,followed bythe neutralinodecayto a grav-itinoandaphoton,aretested.Themeasurementsfortheselected events in data are consistent with the background-only hypoth-esis, and the results are interpreted as limits on the product of crosssectionsandbranchingfractions.Assumingastandardmodel Higgsproductioncrosssection, a 95%CLupperlimitissetonthe branchingfractionofa125 GeV Higgs bosondecayinginto unde-tectableparticlesandoneortwoisolatedphotonsasafunctionof theneutralinomass.Forneutralino massesfrom1to120 GeV an upperlimitintherangeof7to13%isobtained.Furtherresultsare givenasafunctionoftheneutralinolifetime,andalsoforarange ofHiggsbosonmasses.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technicalandadministrative staffsatCERN 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 oftheLHC andtheCMSdetectorprovidedby thefollowingfundingagencies:BMWFWandFWF(Austria);F.R.S. - FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIENCIAS (Colombia); MSES andCSF (Croatia); RPF (Cyprus);

MoER, ERC IUT and ERDF (Estonia); Academy of Finland, MEC, andHIP (Finland);CEAandCNRS/IN2P3(France);BMBF,DFG,and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE andDST (India);IPM (Iran);SFI (Ireland);INFN (Italy); MSIP and NRF(RepublicofKorea);LAS(Lithuania);MOEandUM(Malaysia); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portu-gal);JINR(Dubna);MON,RosAtom,RASandRFBR(Russia);MESTD (Serbia);SEIDIandCPAN(Spain);SwissFundingAgencies (Switzer-land); MST (Taipei); ThEPCenter, IPST, STAR and NSTDA (Thai-land);TUBITAKandTAEK(Turkey);NASUandSFFR(Ukraine);STFC (UnitedKingdom);DOEandNSF(USA).

Individuals have received support from the Marie-Curie pro-gramandtheEuropeanResearchCouncilandEPLANET(European Union); the Leventis Foundation; the A.P. Sloan Foundation; the Alexandervon HumboldtFoundation;theBelgianFederal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); theMinistry ofEducation,Youth andSports (MEYS)of theCzech Republic; the Council of Science and Industrial Research, India; theHOMING PLUS programof theFoundation forPolishScience, cofinanced from European Union, Regional Development Fund; the CompagniadiSan Paolo(Torino); the Consorzioper la Fisica (Trieste); MIUR project 20108T4XTM(Italy); the Thalisand Aris-teia programs cofinanced by EU-ESF and the Greek NSRF; the National Priorities Research Program by Qatar National Research Fund;andRachadapisekSompotFund forPostdoctoralFellowship, ChulalongkornUniversity(Thailand).

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V. Khachatryan,

A.M. Sirunyan,

A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam,

E. Asilar,

T. Bergauer,

J. Brandstetter, E. Brondolin,

M. Dragicevic,

J. Erö,

M. Flechl,

M. Friedl,

R. Frühwirth

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V.M. Ghete,

C. Hartl,

N. Hörmann,

J. Hrubec, M. Jeitler

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, V. Knünz,

A. König,

M. Krammer

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I. Krätschmer, D. Liko,

T. Matsushita, I. Mikulec,

D. Rabady

2

, B. Rahbaran,

H. Rohringer,

J. Schieck

1

,

R. Schöfbeck,

J. Strauss,

W. Treberer-Treberspurg,

W. Waltenberger,

C.-E. Wulz

1

InstitutfürHochenergiephysikderOeAW,Wien,Austria

V. Mossolov,

N. Shumeiko, J. Suarez Gonzalez

NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus

S. Alderweireldt,

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

S. Abu Zeid,

F. Blekman,

J. D’Hondt,

N. Daci, I. De Bruyn, K. Deroover,

N. Heracleous,

J. Keaveney,

S. Lowette,

L. Moreels, A. Olbrechts,

Q. Python,

D. Strom,

S. Tavernier, W. Van Doninck, P. Van Mulders,

G.P. Van Onsem,

I. Van Parijs

VrijeUniversiteitBrussel,Brussel,Belgium

P. Barria,

C. Caillol,

B. Clerbaux,

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H. Delannoy,

G. Fasanella,

L. Favart,

A.P.R. Gay,

A. Grebenyuk,

T. Lenzi,

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A. Marinov,

L. Perniè,

A. Randle-conde, T. Reis,

T. Seva,

C. Vander Velde,

P. Vanlaer,

R. Yonamine,

F. Zenoni,

F. Zhang

3

UniversitéLibredeBruxelles,Bruxelles,Belgium

K. Beernaert,

L. Benucci,

A. Cimmino,

S. Crucy,

D. Dobur,

A. Fagot,

G. Garcia,

M. Gul, J. Mccartin,

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D. Ryckbosch,

S. Salva,

M. Sigamani, N. Strobbe,

M. Tytgat,

W. Van Driessche,

E. Yazgan, N. Zaganidis

GhentUniversity,Ghent,Belgium

S. Basegmez,

C. Beluffi

4

,

O. Bondu,

S. Brochet, G. Bruno,

R. Castello, A. Caudron,

L. Ceard,

G.G. Da Silveira,

C. Delaere,

D. Favart,

L. Forthomme,

A. Giammanco

5

,

J. Hollar, A. Jafari, P. Jez,

M. Komm,

V. Lemaitre, A. Mertens,

C. Nuttens, L. Perrini,

A. Pin,

K. Piotrzkowski,

A. Popov

6

,

L. Quertenmont,

M. Selvaggi,

M. Vidal Marono

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

N. Beliy,

G.H. Hammad

W.L. Aldá Júnior,

G.A. Alves, L. Brito,

M. Correa Martins Junior,

C. Hensel, C. Mora Herrera,

A. Moraes,

M.E. Pol,

P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas,

W. Carvalho, J. Chinellato

7

,

A. Custódio,

E.M. Da Costa,

D. De Jesus Damiao, C. De Oliveira Martins, S. Fonseca De Souza,

L.M. Huertas Guativa,

H. Malbouisson,

D. Matos Figueiredo,

L. Mundim, H. Nogima,

W.L. Prado Da Silva,

A. Santoro,

A. Sznajder,

E.J. Tonelli Manganote

7

, A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahuja

a

,

C.A. Bernardes

b

,

A. De Souza Santos

b

,

S. Dogra

a

,

T.R. Fernandez Perez Tomei

a

,

E.M. Gregores

b

,

P.G. Mercadante

b

,

C.S. Moon

a

,

8

, S.F. Novaes

a

, Sandra S. Padula

a

,

D. Romero Abad,

J.C. Ruiz Vargas

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

A. Aleksandrov,

V. Genchev

†

,

R. Hadjiiska, P. Iaydjiev,

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

M. Ahmad,

J.G. Bian,

G.M. Chen,

H.S. Chen, M. Chen,

T. Cheng,

R. Du,

C.H. Jiang, R. Plestina

9

,

F. Romeo,

S.M. Shaheen,

J. Tao,

C. Wang,

Z. Wang,

H. Zhang

InstituteofHighEnergyPhysics,Beijing,China

C. Asawatangtrakuldee,

Y. Ban,

Q. Li,

S. Liu,

Y. Mao,

S.J. Qian,

D. Wang,

Z. Xu,

W. Zou

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

C. Avila, A. Cabrera,

L.F. Chaparro Sierra,

C. Florez,

J.P. Gomez,

B. Gomez Moreno,

J.C. Sanabria

UniversidaddeLosAndes,Bogota,Colombia

N. Godinovic,

D. Lelas,

D. Polic,

I. Puljak,

P.M. Ribeiro Cipriano

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,

M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic, K. Kadija,

J. Luetic,

S. Micanovic, 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

10

,

M. Finger Jr.

10

CharlesUniversity,Prague,CzechRepublic

A.A. Abdelalim

11

,

A. Awad, A. Mahrous

12

, A. Radi

13

,

14

B. Calpas, M. Kadastik,

M. Murumaa,

M. Raidal,

A. Tiko, C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola, J. Pekkanen,

M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Härkönen,

V. Karimäki,

R. Kinnunen,

T. Lampén,

K. Lassila-Perini,

S. Lehti,

T. Lindén, P. Luukka,

T. 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,

M. Machet, J. Malcles,

J. Rander,

A. Rosowsky, M. Titov,

A. Zghiche

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

I. Antropov, S. Baffioni,

F. Beaudette,

P. Busson,

L. Cadamuro,

E. Chapon,

C. Charlot, T. Dahms,

O. Davignon,

N. Filipovic,

A. Florent,

R. Granier de Cassagnac, S. Lisniak,

L. Mastrolorenzo,

P. Miné,

I.N. Naranjo, M. Nguyen,

C. Ochando,

G. Ortona,

P. Paganini, S. Regnard, R. Salerno,

J.B. Sauvan,

Y. Sirois,

T. Strebler,

Y. Yilmaz,

A. Zabi

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

J.-L. Agram

15

, J. Andrea,

A. Aubin, D. Bloch,

J.-M. Brom, M. Buttignol,

E.C. Chabert, N. Chanon, C. Collard,

E. Conte

15

,

X. Coubez, J.-C. Fontaine

15

,

D. Gelé,

U. Goerlach,

C. Goetzmann,

A.-C. Le Bihan,

J.A. Merlin

2

,

K. Skovpen, P. Van Hove

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

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,

C. Bernet,

G. Boudoul, E. Bouvier,

C.A. Carrillo Montoya,

J. Chasserat,

R. Chierici,

D. Contardo,

B. Courbon,

P. Depasse,

H. El Mamouni, J. Fan,

J. Fay,

S. Gascon,

M. Gouzevitch, B. Ille,

F. Lagarde, I.B. Laktineh,

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

T. Toriashvili

16

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze

10

TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann, S. Beranek,

M. Edelhoff,

L. Feld, A. Heister, M.K. Kiesel,

K. Klein, M. Lipinski,

A. Ostapchuk, M. Preuten,

F. Raupach,

S. Schael,

J.F. Schulte, T. Verlage,

H. Weber,

B. Wittmer,

V. Zhukov

6

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

M. Ata,

M. Brodski,

E. Dietz-Laursonn,

D. Duchardt,

M. Endres, M. Erdmann,

S. Erdweg,

T. Esch,