Search for diphoton resonances in the mass range from 150 to 850 GeV in pp collisions at root s=8 TeV

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REPOSITÓRIO DA PRODUÇÃO CIENTIFICA E INTELECTUAL DA UNICAMP

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https://www.sciencedirect.com/science/article/pii/S0370269315007376

DOI: 10.1016/j.physletb.2015.09.062

Direitos autorais / Publisher's copyright statement:

©2015

by Elsevier. All rights reserved.

DIRETORIA DE TRATAMENTO DA INFORMAÇÃO

Cidade Universitária Zeferino Vaz Barão Geraldo

CEP 13083-970 – Campinas SP

Fone: (19) 3521-6493

http://www.repositorio.unicamp.br

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

diphoton

resonances

in

the

mass

range

from

150

to

850 GeV

in

pp

collisions

at

√

s

=

8

TeV

.

CMS

Collaboration



CERN,Switzerland

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received7June2015

Receivedinrevisedform6September2015 Accepted24September2015

Availableonline30September2015 Editor:M.Doser Keywords: Higgs BSM Diphoton Newscalar 2HDM Graviton

Results arepresented ofasearchforheavyparticlesdecayingintotwophotons.The analysisisbased ona19.7fb−1sampleofproton–protoncollisionsat√s=8TeV collectedwiththeCMSdetectoratthe CERNLHC.Thediphotonmassspectrumfrom150to850 GeV isusedtosearchforanexcessofevents overthe background.The searchisextended tonewresonances withnaturalwidthsofup to10%of themassvalue.Noevidencefornewparticleproductionisobservedandlimitsat95%confidencelevel ontheproductioncrosssectiontimesbranchingfractiontodiphotonsaredetermined.Theselimitsare interpretedintermsoftwo-Higgs-doubletmodelparameters.

©2015CERNforthebenefitoftheCMSCollaboration.PublishedbyElsevierB.V.Thisisanopenaccess articleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.

1. Introduction

Thediscoveryofastandardmodel-likeHiggsbosonattheCERN LHC[1–4]opensanewphaseintheunderstandingofthestandard model(SM)ofparticlephysics.ThesearchforadditionalHiggs-like particlesandthemeasurementoftheirpropertiesprovide comple-mentary ways to test the validity of the SM and to test for the presenceofphysicsbeyondit.

This analysis describes a search for new resonances in the diphotoninvariantmassspectrum,usingdatacorrespondingtoan integratedluminosityof19

.

7fb−1 collectedwiththeCMSdetector atacenter-of-massenergyof8 TeV attheCERNLHC.Despitethe largenonresonantbackground,thediphotondecaymodeprovides a cleanfinal-state topology thatallows the massof thedecaying objecttobe reconstructedwithhighprecision, exploitingthe ex-cellentperformanceoftheelectromagneticcalorimeteroftheCMS experiment.The analysissearchesforlocalexcessesthat couldbe due to the production of particles that decay into two photons withmass in the range from 150to 850 GeV.Both narrow and wideresonancesareinvestigatedwithnaturalwidthsrangingfrom 100 MeV to 10% of the resonance mass. This search covers the diphoton massrange above that investigated in [2,4]. The ATLAS

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

experiment recently published a similar search for narrow reso-nances inthediphoton final state inthemass rangebetween65 and 600 GeV at a center-of-mass energy of 8 TeV [5]. Previous searchesforresonant diphotonprocesseshavebeenperformedat theTevatronby D0[6]andCDF[7]atacenter-of-massenergyof 1.96 TeV andbytheATLAS[8]andCMS[9]experimentsattheLHC atacenter-of-massenergyof7 TeV.

Several models of physics beyond the SM, such as the two-Higgs-doublet model (2HDM) [10], motivate the search for addi-tional high-mass resonances in the diphoton channel. Generally, these models provide an extension of the Higgs sector, where a total of fiveHiggs bosons are predicted by the theory.The mass spectrum ofthe2HDMcan besplitintotwo regions:alight SM-likeHiggsbosonh withmassaround 125 GeV andtheremaining physicalHiggsbosons,H,ascalar,A,apseudoscalar,andH±, clus-teredatanequalorhigherscalewithmH

∼

mA

∼

mH±.Underthe

assumption that thenewly observedHiggsboson isthelight CP-even Higgsscalar ofthe 2HDM, the consistency of its couplings withthosepredictedby theSM pushesthemodelclosetotheso called alignmentlimit [11],where certain decaymodes ofheavy neutralHiggsbosonsvanish,includingH

→

VV (whereVisa vec-tor boson), H

→

hh, and A

→

Z h. At the same time, decays of H and A to

γ γ

and

τ τ

become increasingly important and the electroweakproductionmodes,suchasvectorbosonfusionor pro-http://dx.doi.org/10.1016/j.physletb.2015.09.062

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

ductioninassociationwithaW oraZ boson,are predictedtobe suppressed. Therefore the production of both H and A is domi-nated by gluon fusion. The absence of tree-level flavor-changing neutralcurrents inmultiple-Higgs-doublet theoriesis guaranteed by theGlashow–Weinberg condition [12].This condition is satis-fied in the 2HDM by four discrete combinations of the Yukawa couplingsofthefermionstotheHiggsdoublets.IntheType I sce-narioallfermionscoupletoone doublet,whileinType IIup-type quarkscoupleto one doublet anddown-typequarksandleptons couple to the other. A detailed description of other scenarios is giveninRef.[10].

Giventhegeneralcharacter ofthissearch, theresultscanalso be interpreted interms ofdifferent spin hypothesesfor thenew particle.The Landau–Yang theorem[13,14] forbidsthe direct de-cayofaspin-1particleintoapairofphotons.Thecasesofspin-0 andspin-2 are investigated in this analysis. Spin-2 particles de-cayinginto twophotonsare predictedbyother extensionsofthe SM such as the Randall–Sundrum [15] and the Arkani-Hamed– Dimopoulos–Dvali [16] models. These theories predict a distinct higher-dimensional scenario, which provides an approach to the hierarchyproblemalternativetosupersymmetry.Theparticle pre-dicted in thiscontext, the graviton, can have a mass in the TeV rangeandthus beobservedattheLHCpreferentially initsdecay intotwogaugebosons,suchasphotons.

Thepaper is organized asfollows: aftera brief descriptionof theCMSdetectorinSection2,thedataandsimulatedsamplesare describedinSection3,whilethereconstructionandidentification ofphotonsisdetailedinSection4.Thediphotonvertex identifica-tionis covered inSection 4.3,followed by thedescription ofthe eventselectionandclassificationinSection5.Sections6.1and6.2 describe,respectively,thesignal andbackgroundmodelsusedfor the interpretation of the data, andSection 6.3 discusses the as-sociated systematicuncertainties. Finally,in Section 7the model independentresultsofthesearchfornewdiphotonresonancesand theirinterpretationintermsofthestandaloneproductionand de-cayratesforH andA withinthe2HDMarediscussed.Weexpress theseresultsintermsoftheappropriate2HDMparameters. 2. TheCMSdetector

The central feature of the CMS detector is a superconducting solenoid, of 6 m internal diameter, providing an axial magnetic field of 3.8 T along the beam direction. Withinthe field volume there are a silicon pixel andstrip tracker, a lead tungstate crys-talelectromagneticcalorimeter(ECAL),andabrassandscintillator hadroncalorimeter(HCAL).Charged particletrajectoriesare mea-suredby thetrackersystem, covering0

≤ φ ≤

2

π

inazimuthand

|

η

|

<

2

.

5 inpseudorapidity.

Muonsare measured ingas-ionization detectors embedded in thesteelreturnyoke.TheECAL,whichsurroundsthetracker vol-ume, consistsof 75 848 lead tungstate crystalsthat provide cov-eragein pseudorapidity

|

η

|

<

1

.

48 in the barrelregion (EB) and 1

.

48

<

|

η

|

<

3

.

00 in two endcap regions (EE). The EB modules are arranged in projective towers. A preshower detector consist-ing of two planes of silicon sensors interleaved with a total of 3 radiation lengths of lead is located in front of the EE. In the region

|

η

|

<

1

.

74,theHCALcellshavewidthsof0.087in pseudo-rapidityand azimuth. Inthe

(

η

,

φ)

plane,and for

|

η

|

<

1

.

48,the HCALcellsmaponto5

×

5 ECALcrystalarraystoformcalorimeter towersprojectingradiallyoutwardfromclosetothenominal inter-actionpoint.Atlargervaluesof

|

η

|

,thesizeofthetowersincreases andthematchingECALarrayscontainfewercrystals.Withineach tower,theenergydepositsinECALandHCALcellsaresummedto definethecalorimetertowerenergies,subsequentlyusedto calcu-latethe energiesanddirectionsofhadronicjets. Amore detailed

descriptionofthe CMSdetector,togetherwitha definitionofthe coordinatesystemused andtherelevant kinematicvariables,can befoundinRef.[17].

Photons generallydeposit their energy in a group of crystals of the ECAL called “cluster”. Reconstruction of the photons used inthisanalysisisdescribedinSection 4,andusesaclustering of theenergyrecordedintheECAL,knownasa“supercluster”,which maybe extended in the

φ

direction toform an extendedcluster orgroupofclusters[18].Severalproceduresare usedtocalibrate the energy response of individual crystals before the clustering steps [19]. The changes in the transparencyof the ECAL crystals duetoirradiation during theLHC runningperiodsandtheir sub-sequent recovery are monitored continuously, and corrected for, using light injected from a laser system. The calibration of the ECALisachievedbyexploitingthe

φ

symmetryoftheenergyflow, and by using photonsfrom

π

0

_→

_{γ γ}

_and

_η

_→

_{γ γ}

_{decays and}

electronsfromW

→

e

ν

eandZ

→

e+e− decays[19].

3. Datasamplesandsimulatedevents

The eventsused in theanalysis are selectedby two diphoton triggers withasymmetric transverse momentum thresholds (pT),

26 and 18 GeV or 36 and22 GeV on the leading and sublead-ingphotonsrespectively,dependingonthedatatakingperiod,and complementary photon selections. One selection requires a loose calorimetricidentification basedon theshape ofthe electromag-neticshowerandlooseisolationrequirementsonthephoton can-didates,whilethe otherrequires onlythat thephoton candidates havea highvalue of the R9 shower shapevariable.The R9

vari-able is defined asthe energy sumof 3

×

3 crystalscentered on the mostenergeticcrystalin thesupercluster divided bythe en-ergyofthesupercluster.Photonsthat convertbeforereaching the calorimeter tend to have wider showers andlower values of R9

than unconverted photons. High trigger efficiency is maintained byallowingbothphotonstosatisfyeitherselection.Themeasured triggerefficiencyisabove99.8%foreventssatisfyingthediphoton preselection discussed inSection 4.1required foreventsentering theanalysis.

MonteCarlo(MC)signal andbackgroundeventsare generated using a combinationof programs. Full detector response is sim-ulated with Geant4 [20]. Multiple simultaneous pp interactions (pileup)are simulated,andthe eventsareweighted toreproduce thedistributionofprimaryverticesobservedindata.The interac-tionsusedtosimulatepileuparegeneratedwiththesameversion of pythia[21],v6.424,thatisusedforotherpurposesasdescribed below. The pythia tune usedfor the underlying eventactivity is Z2* [22]. New resonances X are simulated with a natural width of0.1 GeV whichissmallerthanthevalueofthemassresolution inthe energyrangeconsidered. Both spin-0 andspin-2 hypothe-ses are considered. Simulated signal samples of X

→

γ γ

events are generatedwith pythia[21] forthegluon fusionprocess with thefollowing masshypotheses: 150,200, 250,300, 400, 600and 850 GeV. Interference between thesignal andthe background is studied using sherpa 2.1.0 [23,24]. The exclusion limits detailed inSection 7are computedusingeither asignal plus interference template given by sherpa or the Breit–Wigner theoretical model described in Section 6.1.The inclusion of the interferencein our signal model affects the expected and observed upper limitson thesignal yields atthelevelof3% orless.The effectistherefore negligible compared to thesystematic uncertainties, described in Section6.3,andisnotincludedinthefinalresults.Simulated back-grounds include the diphoton continuum process involving two prompt photons, generatedwith sherpa 1.4.2 [23], andprocesses whereone ofthe photoncandidates arisesfrommisidentifiedjet fragments, simulatedwith pythia.These twocontributions

repre-sent 97% ofthe totalbackground inthisanalysis. A lessthan 3% contributionisexpectedfromQCD eventsinwhichboth photons candidatesarisefrommisidentifiedjetfragments;thiscontribution isneglectedintheanalysis.

4. Photonreconstructionandidentification

Photoncandidates forthe analysisare reconstructed from en-ergydepositsinthe ECALusingalgorithms thatconstrain the su-perclustersin

η

and

φ

totheshapesexpectedfromphotonswith high pT.The clustering algorithms account for about98% ofthe

energy of the photons, including those that undergo conversion andbremsstrahlungin the material infront of theECAL. Groups ofclustersareusedtoformsuperclusters.Inthebarrelregion, su-perclustersareformedfromfive-crystal-wide stripsin

η

,centered on the locally mostenergetic crystal (seed), andhave a variable extension in

φ

to take into account the effect of the magnetic fieldonelectronsfromphotonsshoweringbeforeECAL.Inthe end-caps, wherethecrystals arearranged accordingto an x– y rather thanan

η

–

φ

geometry,matricesof5

×

5 crystals,whichmay par-tiallyoverlapandarecenteredontheseedcrystal,aresummedif they lie within a narrow

φ

road.About halfof thephotons con-vertintoe+e− pairsinthematerial upstreamofthe ECAL.Ifthe resultingcharged-particle tracksoriginate sufficientlyclosetothe interaction point to pass through three or more tracking layers, conversiontrack pairs maybe reconstructed andmatchedto the photoncandidate.

Theenergycontainmentofthephotonshowersintheclustered crystalsandthe showerlossesdueto conversionsinthematerial upstreamofthecalorimeterarecorrectedusingamultivariate re-gressiontechniquebasedonaboosteddecisiontree(BDT)[25,26], which uses asinput a collection of shower shape and kinematic variables, together with the energy measured in the preshower for events with photons in the endcaps. Corrections are derived fromsimulation.Inordertocorrectforresidualdiscrepancies be-tween simulationanddata,theMC simulationis tunedto match theenergy resolutionobserved indata, whiledata are calibrated to match the energy response in simulation. More details about photonreconstructioncanbefoundin[18].

Thephoton candidatesused intheanalysisare requiredtobe within the fiducial region,

|

η

|

<

2

.

5, excluding the barrel-endcap transitionregion1

.

44

<

|

η

|

<

1

.

57.

4.1. Photonpreselection

The photon candidates in this analysis are required to satisfy preselectioncriteriasimilartothetriggerrequirements:

•

pγ1 T

>

33GeV and p γ2 T

>

25GeV,where p γ1 T and p γ2 T arethe

transverse momenta of the leading and subleading photons, respectively;

•

aselection on thehadronicleakage of theshower, measured astheratioofenergyinHCALcellsbehindthesuperclusterto theenergyinthesupercluster;

•

a photon identification based on isolation and shape of the shower with lower thresholds with respect the one used in thefinalphotonselectiondescribedinSection4.2;

•

an electron veto, which removes the photon candidateif its superclusterismatched toan electrontrackwithno missing hitsintheinnermosttrackerlayers.

The efficiency of the photon preselection, measured in data us-inga“tag-and-probe”technique[27],rangesfrom94%to99%[2]. Theefficiencyofall preselection criteria,excepttheelectron veto

requirement, is measured using Z

→

e+e− events, while the ef-ficiency for photons to satisfy the electron veto requirement is measured using Z

→

μμγ

events, in which the photon is pro-ducedbyfinalstateradiation,whichprovideamorethan99%pure sourceofpromptphotons.

4.2. Photonidentificationandselection

Photon identification is performed by applying selection re-quirementsonasetofdiscriminatingvariables.Inthisanalysis,the selection is optimized separately infour different pseudorapidity andR9 regions[2].Thevariablesusedtosuppressthebackground

duetothemisidentificationofjetswithhighelectromagnetic con-tentare:

•

the sumofthe transverse momentaof all thetracks coming fromthevertexchosenfortheevent(describedinSection4.3) withinavetoconeof

R

=



(

η

)

2

_{+ ( φ)}

2

₌

₀

_.

_{3 aroundthe}

photoncandidate’sdirection;

•

thesumoftheECALenergydepositsincrystalslocatedwithin avetoconeof

R

=

0

.

3 aroundthesuperclusterposition, ex-cludingthephoton;

•

the sum of the energies of HCAL towers whose centers lie within an annularvetoregionofouter radius

Ro

=

0

.

4 and

inner radius

Ri

=

0

.

15, centered on the ECAL supercluster

position;

•

the ratio betweenthe sumof HCALtower energies within a vetoconeofsize

R

<

0

.

15 centeredontheECALsupercluster position,andtheenergyofthesupercluster;

•

thespreadin

η

oftheelectromagneticcluster,computedwith logarithmicweightsanddefinedas

σ

2 ηη

=



w

_

i

(

η

i

− ¯

η

)

2 wi

,

where

¯

η

=



wiηi



wi and wi

=

max



0

,

4

.

7

+

ln Ei E5×5



,

(1)

and the sum runs over the 5

×

5 crystal matrix around the mostenergeticcrystalinthesupercluster. E5×5 istheenergy

ofthe5

×

5 crystalmatrixand

η

i

=

0

.

0174

η

ˆ

i,where

η

ˆ

i isthe

η

indexoftheithcrystal.Thisvariablerepresentsthesecond momentoftheenergydistributionalongthe

η

coordinate. A moredetaileddescription ofthe isolation requirements canbe found in [18]. The energy deposited within the isolation cones is corrected for the contributionfrom pileup andthe underlying eventusingthe FastJet technique[28].

4.3. Diphotonvertexidentification

Thediphotonmassresolutionhascontributionsfromthe reso-lution ofthe measurementof thephoton energies andthe angle between thetwo photons. The openingangle resolution strongly dependson thedeterminationofthe interactionpoint wherethe twophotonswereproduced.Ifthevertexfromwhichthephotons originateisknownwithaprecisionbetterthan10 mm,the exper-imental resolutionontheanglebetweenthemmakes anegligible contributiontothemassresolution.

Nochargedparticletracksresultfromphotonsthatdonot con-vert,sothediphotonvertexisidentifiedindirectly,usingthe kine-matic propertiesofthediphoton systemanditscorrelationswith the kinematic properties of the recoiling tracks. If either of the photonsconverts,thedirectionoftheresultingtrackscanprovide additionalinformation[2].

Table 1

Definitionofdiphotoneventclasses.

Class ηcriterion R9criterion 0 max(|η|) <1.44 min(R9) >0.94 1 max(|η|) <1.44 min(R9) <0.94 2 1.57<max(|η|) <2.50 min(R9) >0.94 3 1.57<max(|η|) <2.50 min(R9) <0.94

Fig. 1. Signalefficiencytimesacceptanceasafunctionofthemassforaspin-0scalar resonance,producedviagluon–gluonfusion,withnaturalwidthequalto0.1 GeV. Theshadedregionindicatesthesystematicuncertainty.

Theefficiencyforfindingthecorrectvertexforadiphoton res-onance ofmassabove 150 GeV isbetween79% and92% and in-creaseswiththemassoftheresonance.

5. Eventselectionandclassification

The analysis uses events with two photon candidates satis-fying the preselection and identification requirements, and with pγ1

T

>

mγ γ

/

3 and p

γ2

T

>

mγ γ

/

4. The use of pT thresholds scaled

by mγ γ prevents a distortion of the low end of the mγ γ

spec-trumthat would result fromfixed thresholds [29]. This strategy hastwo other main advantages. Background modeling is simpli-fiedbecausetheshapesoftheinvariant massdistributionsinthe differenteventclassesare similarafter thisselection.In addition scaled pT thresholds allow fortighter selection criteria withthe

massincrease,whilepreservingtheacceptanceoftheselection. The search sensitivity is increased by subdividing the events into classes, accordingto indicators of mass resolution and pre-dictedsignal-to-backgroundratio.Twosimpleclassifiersareused: the minimum R9 and the maximum pseudorapidity of the two

photons.PhotonswithahighvalueoftheR9 variableare

predom-inantly unconverted, have a better energy resolution than those withalowervalue,andarelesslikelytoarisefrom misidentifica-tionofjet fragments. Similarly, photonsinthebarrel havebetter energyresolutionthan thosein theendcapandare lesslikelyto beincorrectlyidentified.Theclassificationschemegroupstogether eventswithgooddiphotonmassresolution,resultingfromphotons withgoodenergyresolutionandwithbettersignal-to-background ratio.TheeventclassdefinitionsareshowninTable 1.

Fig. 1 showsthe signal efficiencytimesthe acceptance ofthe event selection as a function of the mass hypothesis for a nar-rowspin-0scalarresonanceproducedviagluon–gluonfusion.The shaded region showsthe systematic uncertainty dueto different sources asdescribed in Section 6.3. The acceptanceover the full massrangeisalsoevaluated forthe pseudoscalarhypothesisand found to be compatible with that measured forthe scalar

reso-Fig. 2. Diphotoninvariantmassdistributionfortheselectedeventsindataand sim-ulation.Backgroundprocessesarerepresentedbythefilledhistograms.Theshaded bandrepresentsthePoissonuncertaintyintheMCprediction.Theprompt dipho-toneventsandthephotonplusjetseventsareshownseparately.Theratiobetween dataandMCisdisplayedbinbybininthebottomplot.Inthisfigure,the leading-ordercrosssectionsfor the backgroundprocesses arescaledto next-to-leading-order(NLO)predictionswithscalefactorsderivedfromCMSmeasurementsat7 TeV

[30,31].

nanceswithintheuncertainties.Forthespin-2scenariothe corre-spondingnumbersareabout5–10%smaller,becauseofdifferences in acceptance betweenthe two models.Fig. 2 shows the dipho-toninvariantmassdistributionforselectedeventsindataandMC simulation, normalized to an integrated luminosity of 19

.

7 fb−1, foralleventclassescombined.Thebinwidthofthisdistributionis chosentobe narrowenough toproperlydisplaywide resonances. However a datadriven technique is exploitedin thisanalysisfor theestimationofthebackground,asdetailedinSection6.2. 6. Statisticalmethodology

Inordertoassessthecompatibilityofthedatawiththe pres-ence of a diphoton resonance, we make a hypothesis test based on a frequentist construction [32,33]. An unbinned maximum-likelihoodfitina slidingwindowrangetothediphotoninvariant mass distributions inall the eventclasses ismade usinga para-metricmodelforthesignal anda backgroundshapeobtained di-rectly fromdata.A scan ofthe signal massandthe signal width is performed. The signal and background normalizations are al-lowed to float,together withthe parameters whichdescribe the background shape. The log-likelihoodratio is used astest statis-tic.Thesignal modelis derivedfromMC simulationasdescribed inSection6.1,withcorrectionsdeterminedfromdata-MC compar-isons applied.The functionalformofthebackgrounddistribution isdeterminedbyfittingthemeasuredmγ γ distributionasdetailed in Section 6.2. Systematic uncertainties described in Section 6.3 areincorporatedintotheanalysisvianuisanceparametersandare treatedaccordingtothefrequentistparadigm[34].

6.1. Signalparametrization

Toconstructthe signal fittingfunction fromsimulatedevents, the reconstructed mγ γ distribution of each event class is

de-scribedintermsofaparametricfunctionofthehypotheticalsignal mass mX.Thisprocedure can beextended ina simplefashion to

allowforanadditionalfreeparameter,thenaturalwidth



Xofthe

newresonance, by convolving a resolution function, which takes intoaccount thedetectorresponse, withatheoretical lineshape. Theconvolutionofthedetectorresponse,describedinthissection, withthetheoreticallineshape,describedinSection6.1.1,isapplied foranynaturalwidthhypothesis.

Thedetectorresponse isparametrizedinterms oftherelative differencebetweenthereconstructeddiphotonmassmreco andthe

truemassmtrue,

μ

= (

mreco

−

mtrue

)/

mtrue.Theresolutionfunction

R is obtained by fitting the response distribution with an ana-lyticfunction,namelythesumoftwosingle-sidedCrystalBall(CB) functions[35]withcommonmean

μ

0 andwidth

σ

,anddifferent

valuesofn and

α

.The CrystalBallfunctioncombinesa Gaussian coreanda power-lawtailwithan exponentn to account for in-completephotonenergycontainmentintheclusterrelatedtothe material infront of the calorimeter,andfor other reconstruction effects: fCB

(

μ

)

=



N

√

2

π σ

exp



−

(

μ

−

μ

0

)

2 2

σ

2



,

for

μ

−

μ

0

σ

>

α

;

N

√

2

π σ



n

|

α

|



n exp



−

|

α

|

2 2



×



n

|

α

|

− |

α

| −

μ

−

μ

0

σ



₋n

,

for

μ

−

μ

0

σ

≤

α

.

(2)

Theparameter

α

definesthetransitionbetweentheGaussianand power-law functions. The fit to the response distribution in the firstclass ofevents fora simulatedsignal withmX

=

150GeV is

showninFig. 3.Theresolutionin

μ

(i.e.,the

σ

inEq.(2))improves by roughly 20%, from 0.021 to 0.016, when the resonance mass increasesfrom150to850 GeV.Theresolutionfunction R is con-structedso that

σ

dependscontinuously onmtrue viaa quadratic

polynomialfunction.

6.1.1. Parametriclineshape

The theoretical line shape of unstable particles is modeled with a Breit–Wigner (BW) distribution with a mass-dependent width[36]: gBW

(

m

|

mX

, 

X

)

=

N

(

m2

₋

_m2 X

)

2

+

m2X



X2

.

(3)

Theeffectoftheprotonpartondistributionfunctions(PDF)onthe signal shape for a wide resonance (with



X

=

0

.

1MX) is

inves-tigated withhigh-mass Higgs boson samples produced with the powheggenerator[37].Theshapeobtainedafterconvolutionwith thePDFisstillwelldescribedbyaBWfunctionwithinanaccuracy betterthan1%.

Thefinal signalmodelisobtainedfromtheconvolutionofthe BWinEq.(3)andtheresponsefunction R:

gS

(

mγ γ

|

mX

, 

X

)

=

R

(

mγ γ

|

m

)

⊗

gBW

(

m

|

mX

, 

X

).

(4)

This signal model is validated by fitting the reconstructed mass distributionforasimulatedsignalwith



X

=

0

.

1GeV,asshownin

Fig. 4.

Fig. 3. FittothedetectorresponsedistributionformX=150GeV withtwo single-sidedCrystalBallfunctions(solidcurve),displayedwithlinear(top)andlogarithmic (bottom)scales.ThedashedanddottedcurvesshowtheindividualCrystalBall com-ponents.

6.2. Backgroundmodeling

Themodeling ofthebackgroundreliesentirelyonthedata,so there are nosystematicuncertainties due topotential mismodel-ingofthebackgroundprocessesbytheMCsimulation.Becausethe exactfunctionalformofthebackgroundineacheventclassisnot known,theparametricmodelmustbeflexibleenoughtodescribe avarietyofpotentialunderlyingfunctions.Usinganincorrect back-ground model can lead to biases in the measured signal yield, which can strongly reduce the sensitivity of the analysis to any potential signal.Theprocedureusedtodeterminethebackground fitting function, which results in a negligible bias, is presented here. In this study the bias on the fitted signal yield is defined asthedifference betweenthenumberoffittedsignal eventsand thenumberofexpectedsignalevents.Asetofanalyticalfunctions that could describe theunknown truebackgrounddistribution in dataisfirst determined.Thefivefunctionsconsideredaspossible truthmodelsare analyticalformsthat areusedindijetresonance searches[38]todescribebothdataandQCDpredictionsand mod-els that are frequently used in diphoton resonance searches [2]. The biasstudyproceduredescribed belowisperformed consider-ingeachfunctionamongtheavailablesetofmodels.Thecandidate fittingfunctionthatperformsbestinthisstudyis f0,theproduct

ofexponentialandpower-lawfunctions:

Fig. 4. ParametrizedsignalshapeforasignalwithmX=150GeV andX=0.1GeV, displayedwithlinear(top)andlogarithmic(bottom)scales.Thesolidcurveshows theresultofafittothesimulatedevents(pointswitherrorbars);thedashedcurve representstheBreit–Wignercomponentofthemodel.

Asanexample,thefitsofthismodeltothedatainthefourevent classesareshowninFig. 5 forthefitrange

[

240

,

640

]

GeV,used for searching for a peak near 350 GeV. In order to check that a background fit model results in a negligible bias in the fitted signalyield,weconstructpseudo-datasetswiththeotherfour an-alyticalmodels by randomly drawing diphotonmass valuesfrom them.Thenumberofbackground eventsgeneratedineach setis equalto the number ofevents observed in datain a fixed mass range.Background-onlypseudo-datasets arethen fittedwiththe signal

+

backgroundprobabilitydensityfunction.Thecriterionfor thebiastobenegligibleisthatitmustbefivetimessmallerthan thestatisticaluncertaintyinthenumberoffittedsignaleventsfor allfourtypesofpseudo-datasetsacrosstheentiremassregionof interest. When this criterion is satisfied, any potential bias from thebackgroundfitfunction can beneglected incomparisonwith thestatistical uncertainty fromthe finite data sample. The func-tionalform ofthe truth modelbeing fixed,the lower andupper boundsofthefitrangearevaried foreachhypotheticalresonance massinordertominimize thebias.Thedesiredfitrangeforeach hypotheticalmass is the one that gives the smallest bias for all thetruth models considered. Thisstudyis performedfora reso-nancewithwidth equal to 10% ofits mass, asthe bias tends to increasewithincreasing resonancewidth. The optimallower and upperboundsofthefitrangeareparametrizedasafunctionofthe resonancemasswithpolynomialfunctions.

As aclosuretest, theobtainedfitranges areused tocompute thebiasonthenumberoffittedsignaleventsasafunctionofthe assumedresonancemass.Wefindthatthe f0 functionproducesa

sufficientlysmallbiasforallfourtruthmodelsinalleventclasses and forany width of the resonance up to 10% ofthe mass.We thereforeusethisbackgroundfunctiontofitthedata.

Ourapproachtoextractthenumbersofsignal andbackground events cannot be usedabove mX

=

850GeV because of thevery

smallnumberof eventsinthe data.Thisistherefore thehighest value of massconsidered inthis search fornewresonances. The lowestvalueofmX consideredis150 GeV,andthefittedrangein

mγ γ is

[

130

,

1000

]

GeV.The maximumvalue ofthewidthofthe

resonanceisfixed to10%ofthe resonancemassitself.Thisvalue islimitedbythewidthoftheresonancemasspointsattheedges oftherange(150 and850GeV)whichhavetobeincludedinthe fittingrange(

[

130

,

1000

]

GeV)withinatleastonesigma.

6.3. Systematicuncertainties

The experimental systematic uncertainties can be separated into those related to the yield and those related to the signal shape.Alog-normal prior isassumedfortheuncertaintiesinthe class yields, while the shape uncertainties are incorporated as parametricvariationsofthemodel.

The normalization uncertainty relatedto the integrated lumi-nosityis2.6%[39].Thephoton-relateduncertainties arethesame asin[2].Theuncertaintyintheenergyscaleisconservatively in-creasedto0.5%inthebarrelandto2%intheendcapstotakeinto account additionalnonlinearities. Systematicuncertainties related to individual photons are then propagated to the signal model, wheretheyresultinuncertaintiesinthepeakpositionandwidth. The1%(2.6%)normalizationuncertaintyinthebarrel(endcap) re-latedtotheofflinephotonidentificationistakenfromthelargest uncertaintyinthedata/MCscalefactorscomputedwithZ

→

e+e− eventsusingthetag-and-probetechnique.A1%normalization un-certaintyisalsoassumedinthetriggerefficiency.Anormalization uncertaintyof2–5%isincludedtotakeintoaccountpossibleevent classmigrationduetoR9 selectionefficiencyuncertaintiesinboth

barrelandendcap. More details abouttrigger and R9 efficiencies

canbefoundinRef.[2].

SystematicuncertaintiesestimatedfortheSM-likeHiggsboson search [2]can be safelyused forthisanalysisas well asforlow mass resonances, where the bulk of the photon pT distribution

is close to that of the photons coming from decays of the SM-like Higgs boson. This is not the casefor high-mass resonances. Thereforeanormalizationuncertaintyof5%perphotonpairisalso includedtoaccountforthedifferencesinthepTspectraofthe

sig-nalphotonsandtheelectronsfromZ

→

e+e−usedtoestimatethe uncertainties[40].

The use of the BW model has an accuracy of the order



X

/

mX[36].Aglobalnormalizationuncertaintyequalto



X

/

mX is

addedtoaccountforanyuncertaintyduetothetheoreticalsignal lineshape.Table 2listsallthesystematicuncertaintiesaccounted forintheanalysis.

7. Resultsandinterpretation

Theinvariantmassspectrashownoclearevidenceforthe pres-enceofa newparticle decayingto two photons. Exclusion limits arethereforecomputed.AmodifiedfrequentistCLs method[32]is

employed,withtheasymptoticapproximationforthestatistictest asdescribedinRef.[41].Model-independentresultsarepresented for a spin-0 and spin-2 resonance produced via gluon–gluon fu-sion. Fig. 6 showsthe 95% confidence level (CL) exclusion limits

Fig. 5. Fitstothediphotonmassdistributionsinthefourclassesofeventsinthewindow[240,640]GeV chosenforsearchingforapeaknear350GeVusingthe f0model andassumingnosignal.Theratiobetweendataand f0isdisplayedbinbybininthebottomplot.

Table 2

Summaryofuncertaintiesthathaveimpactonthesignalstrength, ap-plicabletoeventsinallclasses.

Sourcesofsystematic uncertainty

Uncertainty

Per photon Barrel Endcap Energyresolution,R9>0.94 (lowη,highη) 0.10%, 0.20% 0.14%, 0.06% Energyresolution,R9<0.94 (lowη,highη) 0.10%, 0.18% 0.18%, 0.12%

Photon energy scale 0.5% 2% Photonidentification

efficiency

1.0% 2.6%

Per event Barrel Endcap Integrated luminosity 2.6% 2.6% Vertex finding efficiency 0.2% 0.2% Trigger efficiency 1.0% 1.0% R9class migration 2.3% 5.5% Additionalnormalization uncertainty 5% 5% Breit–Wigner model 0.01–10% 0.01–10%

ontheproductioncrosssectiontimesbranchingfraction(

σ

B

), ob-tainedby combiningall foureventclasses,asa functionofmass for a narrow (



X

=

0

.

1 GeV) spin-2 resonance. Fig. 7 showsthe

95% CLcombinedlimitsfortwo widthhypotheses,



X

=

0

.

1 GeV

and



X

=

0

.

1mX,asafunction ofmassforthespin-0model.The

results shown in Figs. 6 and 7 (top) are similar because of the

Fig. 6. Exclusionlimitat 95%CLonthecrosssectiontimesbranchingfractionof anew,narrow,spin-2resonancedecayingintotwophotonsasafunctionofthe resonancemasshypothesis,combiningthefourclassesofevents.

smalldifferencesintheefficiencytimestheacceptanceinthetwo differentspin scenarios.Fig. 8showsthedependenceofthe limit on



X for two valuesof the resonancemass (150 and840 GeV)

Fig. 7. Exclusionlimitat95%CLonthecrosssectiontimesbranchingfractionofa new,spin-0resonancedecayingintotwophotonsasafunctionoftheresonance masshypothesis,combiningthe fourclassesofevents.Theresults foranarrow resonancehypothesis(X=0.1GeV)(top)andfor awideresonancehypothesis (X=0.1mX)(bottom)areshown.

the production cross section times branching fraction as a func-tion of the resonance mass andwidth in the spin-0 model. The expectedlimitsliebetween6

×

10−4_{pb and4}

_×

₁₀−2_{pb overthe}

fullmassrangeanalyzed.The observedlimitsareconsistentwith theexpectedsensitivityofthe analysisinthe nosignal hypothe-sis.The largest excessis observed atmX

∼

580 GeV witha local

significanceoflessthan2

.

5

σ

.

7.1.Interpretationintwo-Higgs-doubletmodel

Inthissectionthemodel-independentlimitsobtainedfora hy-potheticalheavydiphotonresonanceareinterpretedinthecontext of the two heavy neutral Higgs bosons, H and A, predicted in the 2HDM[11]. In this model,the production cross sectionsfor H andA,aswellasthebranchingfractionsfortheirdecaystotwo photonsdepend on two parameters,

α

and

β

.The mixingangle between H and h is given by

α

, while tan

β

is the ratio of the vacuumexpectationvaluesofthetwo Higgsdoublets.The 2HDM crosssectionsarecalculatedby meansofthe SusHi[42]program, andbranchingfractionsareobtainedusing2HDMC[43].

Exclusion regions in the tan

β

versus cos

(β

−

α

)

plane are shownonlyforthediphotondecayofthepseudoscalarHiggs bo-sonA;noregionofthephasespacecanbeexcludedforthedecay oftheheavyHscalar.

Fig. 8. Exclusion limitat 95% CLon the cross section timesbranching fraction ofanew,spin-0resonancedecayingintotwophotonsasafunctionofthe res-onance width hypothesis,combining the four classesof events.The results for

mX=150(840)GeV areshowntop(bottom).

Fig. 10showstheobservedandexpectedexclusionregionsfor a heavy Higgsboson A of mass 200and300 GeV forthe TypeI 2HDM.ThecasewhereH andA aredegenerateinmassis consid-ered.

In Fig. 10 theregion belowthe curve is excluded.These con-tour plots are similar to those in [10]. The constraints obtained in this analysis on the 2HDM parameters are complementary to those already set by ATLAS on heavy neutral Higgs boson pro-duction usingmultilepton final states[44] andby CMS onheavy neutral Higgsbosons productionusing multilepton anddiphoton finalstates[45,46].

8. Summary

Asearch forresonant productionoftwophotonsisperformed using 19

.

7 fb−1 of pp collisions collected at

√

s

=

8 TeV, in the massrange150–850 GeV.WidthsoftheresonanceX intherange 0.1 GeV to0

.

1mX areinvestigated.Bothspin-0andspin-2

scenar-iosareconsidered.Afittothediphotoninvariantmassdistribution indataisperformedusingaparametricmodelforthesignal and abackgroundshapeobtaineddirectlyfromdata.Noevidencefora signalisobserved,andupperexclusionlimitsat95%CLareseton theproductioncrosssection timesbranchingfraction. The model-independent upper limits extend over considerably wider mass andwidthrangesthan inprevious searches.Wefurther interpret

Fig. 9. Combinedobserved(top)andexpected(bottom)exclusionlimitsat95%CL onthecrosssectiontimesbranchingfractionofanew,spin-0resonancedecaying intotwophotonsasafunctionoftheresonancemassandwidthhypotheses. Con-toursaredisplayedfordifferentvaluesofσB(X→γ γ).(Forinterpretationofthe colorsinthisfigure,thereaderisreferredtothewebversionofthisarticle.)

theselimitsinthecontextofthe2HDM,presentingexclusion con-toursinthetan

β

versus cos

(β

−

α

)

plane.Thisisthefirstsearch forheavy diphotonresonancescarriedoutattheLHCtobe inter-pretedintermsofthe2HDM.

Acknowledgements

We congratulate our colleagues in the CERN accelerator de-partments for the excellent performance of the LHC and thank thetechnicalandadministrativestaffs atCERN andatother CMS institutes for their contributions to the success of the CMS ef-fort.Inaddition,wegratefullyacknowledgethecomputingcenters and personnel of the Worldwide LHC Computing Grid for deliv-eringso effectively the computinginfrastructure essential to our analyses. Finally, we acknowledge the enduring support for the constructionandoperationoftheLHCandtheCMSdetector pro-videdbythefollowingfundingagencies:theAustrianFederal Min-istryof Science,Research andEconomy andthe Austrian Science Fund;the Belgian Fonds de laRecherche Scientifique,and Fonds voorWetenschappelijkOnderzoek;theBrazilianFundingAgencies (CNPq,CAPES,FAPERJ,andFAPESP);theBulgarianMinistryof Edu-cationandScience;CERN; theChinese AcademyofSciences, Min-istryofScienceandTechnology ofthePeople’sRepublicofChina, andNationalNaturalScienceFoundation ofChina;theColombian

Fig. 10. Observedandexpected95%CLexclusionregionsforgluon-fusion produc-tionofaheavyHiggsbosonA ofmass200 GeV (top)and300 GeV (bottom)inthe tanβversuscos(β−α)planefortheTypeI2HDM,assumingtheH bosontobe degenerateinmasswithA.Theregionsbelowthecurvesareexcluded.

Funding Agency(COLCIENCIAS); the Croatian Ministryof Science, Education and Sports, and the Croatian Science Foundation; the ResearchPromotionFoundation,Cyprus;theMinistryofEducation andResearch,EstonianResearchCouncil viaIUT23-4andIUT23-6 and European Regional DevelopmentFund, Estonia; the Academy ofFinland,FinnishMinistryofEducationandCulture,andHelsinki Institute of Physics; the Institut National de Physique Nucléaire etde Physique desParticules/CNRS,andCommissariatà l’Énergie Atomique et aux Énergies Alternatives/CEA, France; the Bundes-ministerium für Bildung und Forschung, Deutsche Forschungs-gemeinschaft,andHelmholtz-GemeinschaftDeutscher Forschungs-zentren, Germany;the GeneralSecretariatforResearchand Tech-nology, Greece; the National Scientific Research Foundation, and National Innovation Office, Hungary; the Department of Atomic Energy, Government ofIndia and the DepartmentofScience and Technology, India; the Institute for Studies inTheoretical Physics and Mathematics, Iran; the Science Foundation Ireland; the Isti-tuto Nazionale di Fisica Nucleare, Italy; the Ministry of Science, ICTandFuturePlanning,andNationalResearchFoundationof Ko-rea (NRF),RepublicofKorea;theLithuanianAcademyofSciences; theMinistryofEducation,andUniversityofMalaya(Malaysia);the MexicanFundingAgencies(CINVESTAV,CONACYT,SEP,and UASLP-FAI); the Ministryof Business, Innovation andEmployment, New Zealand; the Pakistan Atomic Energy Commission; the Ministry of Science and Higher Education and the National Science

Cen-tre,Poland;theFundação paraaCiênciae aTecnologia, Portugal; JINR,Dubna;theMinistryofEducationandScienceoftheRussian Federation, the Federal Agency of Atomic Energy of the Russian Federation, Russian Academy of Sciences, andthe Russian Foun-dationforBasic Research; theMinistryof Education,Science and TechnologicalDevelopmentofSerbia; theSecretaría de Estado de Investigación, Desarrollo e Innovación and Programa Consolider-Ingenio2010,Spain;theSwissFundingAgencies(ETHBoard,ETH Zurich,PSI,SNF, UniZH,Canton Zurich, andSER);the Ministryof ScienceandTechnology,Taipei;the ThailandCenterofExcellence inPhysics,theInstituteforthePromotionofTeachingScienceand TechnologyofThailand,SpecialTask ForceforActivatingResearch andthe NationalScienceandTechnology DevelopmentAgencyof Thailand;theScientific andTechnical ResearchCouncil ofTurkey, and Turkish Atomic Energy Authority; the National Academy of Sciences of Ukraine,and State Fund for Fundamental Researches, Ukraine;theScienceandTechnologyFacilitiesCouncil,UK;theUS DepartmentofEnergy,andtheUSNationalScienceFoundation.

Individuals have received support from the Marie-Curie pro-gramandtheEuropeanResearchCouncilandEPLANET(European Union); the Leventis Foundation; the A.P. Sloan Foundation; the AlexandervonHumboldt Foundation;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); theMinistryofEducation, YouthandSports (MEYS)ofthe Czech Republic;theCouncilofScienceandIndustrialResearch,India;the HOMING PLUSprogram ofthe Foundation forPolish Science, co-financed from European Union, Regional Development Fund; the CompagniadiSanPaolo(Torino);theConsorzioper laFisica (Tri-este); MIUR project 20108T4XTM (Italy); the Thalis and Aristeia programs cofinanced by EU-ESF and the Greek NSRF; and the National Priorities Research Program by Qatar National Research Fund.

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CMSCollaboration

V. Khachatryan,

A.M. Sirunyan,

A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam,

E. Asilar,

T. Bergauer,

J. Brandstetter,

E. Brondolin,

M. Dragicevic,

J. Erö,

M. Flechl,

M. Friedl,

R. Frühwirth

1

,

V.M. Ghete,

C. Hartl,

N. Hörmann,

J. Hrubec,

M. Jeitler

1

,

V. Knünz,

A. König,

M. Krammer

1

,

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,

G. De Lentdecker,

H. Delannoy,

D. Dobur,

G. Fasanella,

L. Favart,

A.P.R. Gay,

A. Grebenyuk,

T. Lenzi,

A. Léonard,

T. Maerschalk,

A. Mohammadi,

L. Perniè,

A. Randle-conde,

T. Reis,

T. Seva,

L. Thomas,

C. Vander Velde,

P. Vanlaer,

J. Wang,

F. Zenoni,

F. Zhang

3

UniversitéLibredeBruxelles,Bruxelles,Belgium

K. Beernaert,

L. Benucci,

A. Cimmino,

S. Crucy,

A. Fagot,

G. Garcia,

M. Gul,

J. Mccartin,

A.A. Ocampo Rios,

D. Poyraz,

D. Ryckbosch,

S. Salva Diblen,

M. Sigamani,

N. Strobbe,

M. Tytgat,

W. Van Driessche,

E. Yazgan,

N. Zaganidis

GhentUniversity,Ghent,Belgium

S. Basegmez,

C. Beluffi

4

,

O. Bondu,

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,

T. Caebergs,

G.H. Hammad

UniversitédeMons,Mons,Belgium

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

2

,

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

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

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,

M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,

K. Kadija,

J. Luetic,

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. Ali

11

,

12

_,

_{R. Aly}

13

_,

_{S. Aly}

13

_,

_{Y. Assran}

14

_,

_{A. Ellithi Kamel}

15

_,

_{A. Lotfy}

16

_,

_{M.A. Mahmoud}

16

_,

_{R. Masod}

11

_,

A. Radi

12

,

11

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

B. Calpas,

M. Kadastik,

M. Murumaa,

M. Raidal,

A. Tiko,

C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,

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,

J. Pekkanen,

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

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

17

,

J. Andrea,

A. Aubin,

D. Bloch,

J.-M. Brom,

M. Buttignol,

E.C. Chabert,

N. Chanon,

C. Collard,

E. Conte

17

,

J.-C. Fontaine

17

,

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

9

,

G. Boudoul,

E. Bouvier,

S. Brochet,

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,

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

Z. Tsamalaidze

10

InstituteofHighEnergyPhysicsandInformatization,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,

J. Sammet,

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,

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,

T. Pook,

M. Radziej,

H. Reithler,

M. Rieger,

F. Scheuch,

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. Lingemann

2

,

A. Nehrkorn,

A. Nowack,

I.M. Nugent,

C. Pistone,

O. Pooth,

A. Stahl

M. Aldaya Martin,

I. Asin,

N. Bartosik,

O. Behnke,

U. Behrens,

A.J. Bell,

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,

E. Gallo,

J. Garay Garcia,

A. Geiser,

A. Gizhko,

P. Gunnellini,

J. Hauk,

M. Hempel

18

,

H. Jung,

A. Kalogeropoulos,

O. Karacheban

18

,

M. Kasemann,

P. Katsas,

J. Kieseler,

C. Kleinwort,

I. Korol,

W. Lange,

J. Leonard,

K. Lipka,

A. Lobanov,

W. Lohmann

18

,

R. Mankel,

I. Marfin

18

,

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,

M.Ö. Sahin,

J. Salfeld-Nebgen,

P. Saxena,

T. Schoerner-Sadenius,

M. Schröder,

C. Seitz,

S. Spannagel,

K.D. Trippkewitz,

C. Wissing

DeutschesElektronen-Synchrotron,Hamburg,Germany

V. Blobel,

M. Centis Vignali,

A.R. Draeger,

J. Erfle,

E. Garutti,

K. Goebel,

D. Gonzalez,

M. Görner,

J. Haller,

M. Hoffmann,

R.S. Höing,

A. Junkes,

R. Klanner,

R. Kogler,

T. Lapsien,

T. Lenz,

I. Marchesini,

D. Marconi,

D. Nowatschin,

J. Ott,

F. Pantaleo

2

,

T. Peiffer,

A. Perieanu,

N. Pietsch,

J. Poehlsen,

D. Rathjens,

C. Sander,

H. Schettler,

P. Schleper,

E. Schlieckau,

A. Schmidt,

J. Schwandt,

M. Seidel,

V. Sola,

H. Stadie,

G. Steinbrück,

H. Tholen,

D. Troendle,

E. Usai,

L. Vanelderen,

A. Vanhoefer

UniversityofHamburg,Hamburg,Germany

M. Akbiyik,

C. Barth,

C. Baus,

J. Berger,

C. Böser,

E. Butz,

T. Chwalek,

F. Colombo,

W. De Boer,

A. Descroix,

A. Dierlamm,

M. Feindt,

F. Frensch,

M. Giffels,

A. Gilbert,

F. Hartmann

2

,

U. Husemann,

F. Kassel

2

,

I. Katkov

6

,

A. Kornmayer

2

,

P. Lobelle Pardo,

M.U. Mozer,

T. Müller,

Th. Müller,

M. Plagge,

G. Quast,

K. Rabbertz,

S. Röcker,

F. Roscher,

H.J. Simonis,

F.M. Stober,

R. Ulrich,

J. Wagner-Kuhr,

S. Wayand,

T. Weiler,

C. Wöhrmann,

R. Wolf

InstitutfürExperimentelleKernphysik,Karlsruhe,Germany

G. Anagnostou,

G. Daskalakis,

T. Geralis,

V.A. Giakoumopoulou,

A. Kyriakis,

D. Loukas,

A. Markou,

A. Psallidas,

I. Topsis-Giotis

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

A. Agapitos,

S. Kesisoglou,

A. Panagiotou,

N. Saoulidou,

E. Tziaferi

UniversityofAthens,Athens,Greece

I. Evangelou,

G. Flouris,

C. Foudas,

P. Kokkas,

N. Loukas,

N. Manthos,

I. Papadopoulos,

E. Paradas,

J. Strologas

UniversityofIoánnina,Ioánnina,Greece

G. Bencze,

C. Hajdu,

A. Hazi,

P. Hidas,

D. Horvath

19

,

F. Sikler,

V. Veszpremi,

G. Vesztergombi

20

,

A.J. Zsigmond

WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni,

S. Czellar,

J. Karancsi

21

,

J. Molnar,

Z. Szillasi

InstituteofNuclearResearchATOMKI,Debrecen,Hungary

M. Bartók

22

,

A. Makovec,

P. Raics,

Z.L. Trocsanyi,

B. Ujvari

UniversityofDebrecen,Debrecen,Hungary

P. Mal,

K. Mandal,

N. Sahoo,

S.K. Swain

NationalInstituteofScienceEducationandResearch,Bhubaneswar,India

S. Bansal,

S.B. Beri,

V. Bhatnagar,

R. Chawla,

R. Gupta,

U. Bhawandeep,

A.K. Kalsi,

A. Kaur,

M. Kaur,

R. Kumar,

A. Mehta,

M. Mittal,

N. Nishu,

J.B. Singh,

G. Walia