A measurement of the Higgs boson mass in the diphoton decay channel

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

A

measurement

of

the

Higgs

boson

mass

in

the

diphoton

decay

channel

.

The

CMS

Collaboration



CERN,Switzerland

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory: Received15February2020 Receivedinrevisedform8April2020 Accepted9April2020

Availableonline15April2020 Editor:M.Doser

Keywords:

CMS Higgs diphoton

A measurement of the mass of the Higgs boson in the diphoton decay channel is presented. This analysis is based on 35.9 fb−1_{of proton-proton collision data collected during the 2016 LHC running period, with} the CMS detector at a centre-of-mass energy of 13 TeV. A refined detector calibration and new analysis techniques have been used to improve the precision of this measurement. The Higgs boson mass is measured to be mH=125.78 ±0.26 GeV. This is combined with a measurement of mHalready performed in the H→ZZ→4decay channel using the same data set, giving mH=125.46 ±0.16 GeV. This result, when further combined with an earlier measurement of mHusing data collected in 2011 and 2012 with the CMS detector, gives a value for the Higgs boson mass of mH=125.38 ±0.14 GeV. This is currently the most precise measurement of the mass of the Higgs boson.

©2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3_.

1. Introduction

TheindependentobservationsoftheHiggsbosonbytheATLAS and CMS Collaborations [1–3] in proton-proton collisions at the CERNLHCwasakeymilestoneintheunderstandingofthe mech-anismofelectroweaksymmetrybreaking.Morerecently,withthe increasedamountofdataresultingfromthehigherenergyandthe higherluminosityaccumulatedattheLHCbetween2015and2018 (Run2),thefocushasshiftedfromobservationtoprecision mea-surementsof its properties.The couplings of the Higgsboson to otherelementaryparticlescanbepredictedbythestandardmodel ofparticlephysics onceitsmassisknown.Thismotivatesprecise measurementsofthemassoftheHiggsboson(mH)inallavailable

decaychannels.

Although the H

→

γ γ

decay channel has a small (

≈

0.23%) branchingfraction,itprovidesacleanfinalstatetopologyinwhich thediphotoninvariantmasscanbereconstructedwithhigh preci-sion.Themeasurement ofmH inthisdecaychannel canbe

com-bined withmeasurements in other decaychannels to achieve an even higher precision. In this way the ATLAS and CMS Collabo-rations measured mH to be 125.09

±

0.24GeV [4] with the data

collectedin2011and2012(Run1).

In this Letter, we present a new measurement of mH in the

H

→

γ γ

decay channel with the data collected at

√

s

=

13TeV in 2016 corresponding to an integrated luminosity of 35.9 fb−1. TheCMSCollaborationhaspreviously reportedameasurementof

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

mH with the same data set in the H

→

ZZ

→

4 decay channel

where mH was measured to be 125.26

±

0.21GeV [5]. The

AT-LAS collaboration have also published a measurement of mH of

124.97

±

0.24GeV [6], using thecombined 2016and Run1 data sets. Our measurements of mH with the 2016 data set, in the

H

→

γ γ

andH

→

ZZ

→

4decaychannels, havebeen combined withourmeasurement ofmH withtheRun1dataset. The

com-bined resultandthe procedurefollowed forthiscombinationare alsodescribedinthisLetter.

2. The CMS detector

The central feature of the CMSdetector is a superconducting solenoidof6 m internaldiameterwithauniformmagneticfieldof 3.8 T. Inside themagnet volumeare siliconpixel andstrip track-ers, a lead tungstate crystal electromagnetic calorimeter (ECAL), andabrassandscintillator hadroncalorimeter,each composedof a barrel and two endcap sections.Gas-ionisation chamber based muondetectorsareembeddedinthesteelflux-returnyokeoutside the solenoid. The ECAL is a hermetic homogeneous calorimeter made of61 200 lead tungstate (PbWO4) crystals mounted in the

centralbarrelpart,closedby7324crystalsineachofthetwo end-caps. Intheregion 1.65

<

|

η

|

<

2.6 athree-radiation-length-thick preshowerdetectorwithtwo orthogonallayers ofsiliconstripsis placed infrontofthe endcapcrystals.Avalanche photodiodesare used asphotodetectorsinthe barrelandvacuumphototriodes in the endcaps. The barrel part of the ECAL (EB) covers the pseu-dorapidityrange

|

η

|

<

1.479,whiletheendcapcalorimeterscover therange1.479

<

|

η

|

<

3.0.Acalorimeterwithlongitudinalquartz

https://doi.org/10.1016/j.physletb.2020.135425

0370-2693/©2020TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

fibrescomplementsthe coverageprovidedby thebarreland end-cap detectors. The first level of the CMS trigger system [7] uses information from the calorimeters and muon detectors to select the most interesting events in a fixed time interval of lessthan 4 μs. The high-level trigger processor farm further decreases the eventratefromaround100 kHz toaround1 kHz beforedata stor-age.AmoredetaileddescriptionoftheCMSdetector,togetherwith a definitionof the coordinatesystem andthe relevant kinematic variables,canbefoundinRef. [8].

3. Analysis strategy

The general strategy followed in this analysis is the same as thatadoptedinanearlieranalysisbytheCMSCollaborationofthe Higgsbosonpropertiesinthediphotonchannel [9].Sincethat pub-lication, refinements were madeto increase the precision ofthe measurement of mH through a better understanding of the

sys-tematic uncertainties of the measurement, and a more accurate detector calibration was performed. We have also improved the method,first introduced inRef. [10], to measure andcorrect for nonlinear discrepancies in the energy scale with transverse mo-mentum(pT),ofelectronsfromZbosondecay,betweendataand

simulation by increasing the granularityof the correction.In ad-dition, we have developed a method to evaluate the systematic uncertaintyofthephotonenergyscaleduetoradiationdamageof theECALcrystals,andasimplifiedeventcategorisation, described inSection6,isfollowedintheanalysis.

Withthenewcalibration,thedetectorresponseismorestable withtime,leading to areduction oftheuncertainties in the cor-rectionstothephotonenergyduetothematerialupstreamofthe ECALandoftheuncertaintiesassociatedwithvariableswhich de-scribetheelectromagneticshower.

4. Data and simulation

The events used in thisanalysis were collected in 2016 with an integrated luminosity of35.9 fb−1.They were selected witha diphoton trigger that had asymmetric pT thresholds of 30 and

18 GeV.Fulldetailsofthetriggerselectionandthemeasurementof thetriggerefficiencycanbefoundinRef. [9].Tomodelthesignal andbackgroundprocesses,eventsaregeneratedwithMonteCarlo techniques.ThedetailedresponseoftheCMSdetectorissimulated usingthe Geant4 package [11].

Signal events are simulated with the MadGraph5_amc@nlo v2.2.2matrix-elementgenerator [12] atnext-to-leadingorderand interfacedwith pythia 8.205 [13] forpartonshoweringand hadro-nisation. The pythia underlying event tune CUETP8M1 [14] was used. The irreducible prompt diphoton background and the re-ducible backgrounds of

γ

+ jet and multijet events, where the jetsare misidentifiedasisolated photons,arethedominant back-groundstothe H

→

γ γ

decayprocess. Thediphoton background ismodelledwiththe sherpa v.2.2.1 [15] generator,whichincludes the Born processes with up to 3 additional jets at leading or-der (LO) accuracy, as well as the LO box processes. The

γ

+jets andmultijetbackgrounds are modelled with pythia at LO. These samples are used for the training of the multivariate discrimi-nantsused inthisanalysis,aswell asfortheoptimisationofthe event categorisation. The Drell–Yan samples used to derive the electron and photon energy scale corrections and their system-atic uncertainties, are simulated with MadGraph [16] and Mad-Graph5_amc@nlo generatorsandmergedtogetherinorderto im-provethestatisticalprecisionofthescalecorrections.Before merg-ingthesesamples,thecompatibilityofthemeelineshapesbetween

the two generators in the categories used to derive the electron andphotonenergyscalecorrectionswasconfirmed.

Fig. 1. EnergyscalecorrectionsasafunctionofthepTofthephoton.Thehorizontal barsintheplotrepresentthevariablebinwidth.Thesystematicuncertainty associ-atedwiththiscorrectionisapproximatelythemaximumdeviationobservedinthe

pTrangebetween45and65 GeV forelectronsintheEBregion.

The simulation includes multiple proton-proton interactions takingplacewithinabunchcrossing,knownas‘pileup’.Pileupcan occur not only in the same bunch crossing (in-time pileup), but also inthe crossingof previous andsubsequentbunches (out-of-time pileup), both ofwhich are accountedforby the simulation. The simulated events are scaled to reproduce the distribution of thenumberofpileupinteractionsindata.

5. Photon reconstruction and identification

Photon candidates are reconstructed as energy deposits in a collectionofcrystalsintheECAL.Aclusterisformedbyfirst iden-tifyinga‘seed’crystalwithanenergyaboveagiventhreshold,then theclusterisbuiltbyfindingthecrystalsthatshareanedgewith theseed crystalandhaveanenergyaboveanother,lower thresh-old. This second threshold is set to be approximately 80 MeV in the barrel and ranging from 80 to 300 MeV in the endcaps, de-pendingon

|

η

|

.Theseclusters,onceformed,arecombinedtoform a‘supercluster’, aimingtofullycontaintheshowerofthephoton. Thisprocedureaccountsforvariationsingeometryasafunctionof

|

η

|

,andoptimises therobustnessoftheenergyresolutionagainst pileup.

5.1. Photonenergycalibration

Acriticalcomponentofthemeasurement ofmH istheenergy

calibrationoftheresponse oftheECALtophotons. Theenergyof a photon is calculated by summing the calibrated and corrected energy [17] ofall crystalsin theassociated supercluster, andthe energydeposited inthepreshowerintheregion 1.65

<

|

η

|

<

2.6 covered by this detector. For each supercluster, a shower shape variable R9 isdefined, whichis used toselect photons

undergo-ing a conversion in the material between the interaction point and the front face of the ECAL.The variable R9 isdefined for a

candidate electromagnetic cluster as theratio of the sumof en-ergydepositedina3

×

3 crystalarray,centredonthecrystalwith the highestenergy,to thesumofthe energyinthe supercluster. Theenergydepositionofphotonsthatconvertbeforereachingthe calorimetertendstohavewidertransverseprofilesandthuslower values of R9 than those ofunconverted photons.To further

opti-misetheenergyresolution,theenergyiscorrectedforthelackof completecontainmentoftheelectromagneticshowersinthe clus-tered crystals, the energylost by photons that convertupstream

Fig. 2. Comparisonofthedistributionsofthe invariantmassofthedielectronsindataandsimulationinZ→ee eventsafterapplicationofenergycorrectionsintwo representativecategories.Left:BothelectronsareintheEBandsatisfyR9>0.94.Right:theleadingelectronhasatransversemomentumbetween55and65 GeV,without arequirementonthesecondelectron.Thesystematicuncertaintyintheerrorbandintheplotsincludeonlytheuncertaintiesonthederivedenergyscalecorrections.

ofthecalorimeter,andtheeffectsofpileup.Thesecorrectionsare derivedusingamultivariateregressiontechnique,trainedon sim-ulatedevents, which simultaneously estimates the energyof the photon andits median uncertainty.The inputs to thisregression are shower shape variables, the preshower information, and ob-servablessensitivetopileup [18].

After applying these corrections to the photon energy, some residual differences remain between the data and simulation in boththephotonenergyscaleandtheresolution.Amultistep pro-cedureisusedtocorrectthesedifferences,usingZ

→

ee decaysin whichtheelectronshowersare reconstructedasphotons,so that thesimulationaccurately reproducesthedata.Inthe firststepof thisprocess, any residuallong-term drifts in the energyscale in data are corrected for, in approximately 18-hour intervals corre-spondingto one LHC fill. In the second step, correctionsto both theenergy resolution inthe simulation, andthe scale correction neededforthedataare derivedsimultaneouslyinbinsof

|

η

|

and

R9 for electrons.The energy resolutionobtained insimulation is

matchedto thedataby addinga Gaussian smearingterm, deter-mined by adjusting the agreement inthe Z

→

ee invariant mass distributions.In the third andfinal step the energyscale correc-tionsarederivedinbinsof

|

η

|

andpTtoaccountforanynonlinear

responseofthecrystalswithenergy.Thecorrectionsobtainedfrom thisstepareshowninFig.1forelectronsasafunctionofpTinthe

threebinsof

|

η

|

inEB.Thisadditionalstepinthescalecorrection improvesthe precision ofthe measurement ofmH,since the

en-ergyspectrumoftheelectronsfromZbosondecay(



pT



≈

45GeV)

usedto derive the scalecorrections, isdifferent fromthe energy spectrumofphotonsfromHiggsbosondecay(



pT



≈

60GeV).

Wenotethat inthesecondstepthenumberofbinsin R9 for

thescalecorrectionshasbeenincreasedbyafactoroffiveoverthe previousanalysis [9],resultinginanimprovementintheprecision withwhichthe energyscale isdetermined.Also,inorderto pro-videaconsistencytestofthederivationprocedure,thecorrection factorsthatareobtainedinthesecondandthirdstepsareapplied asecondtimetothedataandanewsetoffactorsisextractedin thesameelectroncategories.Anydeviationfromunityisan indi-cationofthenonclosureofthederivationprocedureandisapplied asasystematicuncertaintyonscalecorrections.

The agreementbetweendata andsimulationinthe dielectron invariant mass, afterapplying theseenergy scale correctionsand theadditional smearings,is showninFig.2 fordielectronevents intheEBwithR9greaterthan0.94,andfordielectroneventswith

aleading transversemomentum between55and65 GeV,without a requirementon the second electron. The former demonstrates the performance of the energy corrections on photons with the highesteventcount,optimalresolution,andthehighestsensitivity totheHiggsbosonmass.Thelatterdemonstratesthat theenergy correctionsareeffectiveinakinematicregionwherethepT ofthe

electronhasbeenchosentobethetypical pT ofa photonfroma

Higgsbosondecay.Inbothcasesdataandsimulationare ingood agreementinthecoreofthedistributions.

5.2. Photonpreselectionandidentification

The photons considered in the subsequent steps of this anal-ysis are required to satisfy certain preselection criteria that are similar to,butmorestringentthan,those imposed bythe trigger requirements.Adetaileddescriptionofthesepreselectioncriteria, aswellasthemethodsemployedtoevaluatetheirefficiencies,can be found in Ref. [9]. A dedicated boosted decision tree (BDT) is usedtoclassifypromptphotonsfromotherphotoncandidatesthat ariseoutofmisidentifiedjetfragments,butwhichsatisfythe pres-electioncriteria.Thefulldetailsoftheinputfeaturesofthisphoton identification BDT is also described in Ref. [9]. The score of this BDTisusedlaterintheeventcategorisation,discussedinthenext section.

5.3. Vertexselection

The identification of the diphoton vertex position along the beam axishas a direct impact on the diphoton mass resolution, since if the vertex position is known to better than about 1 cm, then the invariant mass resolution is dominated by the photon energy resolution. The distribution of the position of the inter-action verticesalong the beamaxis hasan RMS spread ofabout 3.4 cm, and, in typical pileup conditions in 2016, there were on averagearound23interactionsineachbunchcrossing.Thechoice of thediphoton vertex ismade followingthe same procedure in

Ref. [9]:aBDT,whoseinputsareobservablesrelatedtotracks re-coilingagainst the diphoton system, isused to identifythe most likely vertex. A second BDT is used to determine the probability ofcorrectlychoosing that vertex. Thescore ofthe second BDTis usedlater intheeventcategorisation, discussed below.The algo-rithm isvalidatedusing Z

→ μ

+

μ

− eventswiththe muontracks removedso astomimic diphotonpair production.The efficiency ofassigningtheeventtoavertexwithin1 cm ofthetruevertexin thesimulatedH

→

γ γ

eventsisfoundtobeapproximately81%. 6. Event classification

TheeventselectionprocedureissimilartothatinRef. [9].The

pT of the two leading photons (pγT1, p γ2

T ) are required to

sat-isfy pγ_T1

>

mγ γ

/3 and

p_Tγ2

>

mγ γ

/4,

wheremγ γ isthediphoton mass,andthe photon pT requirementis applied afterthe vertex

assignment.Additionally mγ γ isrequiredtobe between100and 180 GeV.TheuseofpT thresholdsscaledwiththediphoton

invari-antmassistopreventadistortionofthelowerendoftheinvariant massspectrum.Thesuperclustersofbothphotonsarerequiredto have

|

η

|

<

2.5 and to be outsideof the barrel-endcap transition region,1.44

<

|

η

|

≤

1.57.

Toimprovethesensitivityofthe analysis,eventsare classified according to their production mechanism, mass resolution, and their predicted signal-to-background ratio. A dedicated classifier, referred toasthe diphotonBDT, isused todiscriminate between signal and background events. This BDT assigns a high score to eventswithphotonsexhibitingsignal-likekinematics,agoodmass resolution, anda high score fromthe photon identification BDT. Theper-eventprobabilityestimateofassigningthecorrectprimary vertextothediphotonsystemisusedasoneoftheinputfeatures of this diphoton BDT. The other input features are described in Ref. [9].

Nearly 95% ofHiggs boson eventscome from two production modes. Theseare gluon-gluon fusion(ggH) andvector boson fu-sion(VBF),wheretherearetwojetsinthefinalstateseparatedby alargerapidity gap.Amultivariatediscriminantistrainedto dis-criminateVBFeventsfromggH+jetsevents,usingthekinematics ofthecharacteristicVBF dijetsystemasinputs. Thisdiscriminant is then given as an input to an additional multivariate classifier (VBFcombinedBDT)alongwiththescorefromthediphotonBDT, andtheratio pγ γ_T

/

mγ γ .TheVBFeventsaresubdividedintothree categoriesbased onthe VBFcombined BDT score.The remaining events are mostly ggH events and are designated as ‘untagged’. Theseeventsarefurthersubdividedintofourcategoriesbasedon theirdiphotonBDTscore.

Adding other possible analysiscategories, where for example, theHiggsbosonisproducedinassociationwithavectorboson,or withapairoftopquarks,addsonlyasmallincrementtothe preci-sionofthemassmeasurementatthecostofasignificantincrease intheanalysiscomplexity.Thus,unlike intheearlieranalysis [9], theseproductionmodesarenotconsidered asseparate categories inthisanalysis.

7. Signal and background models

InordertoextractmH,signalandbackgroundmodelsare

con-structed to fit the diphoton mass distributions observed in the data.The signal modelsare derived using simulatedHiggsboson events,whilethebackgroundmodelsused inthefitsofthemγ γ

spectraarederiveddirectlyfromdata.

7.1. Signalmodel

The resolution ofmH in the diphoton decay channel depends

ontheproductionmechanismandtheanalysiscategory.Hencethe

signalshapesusedtomodelthediphotoninvariantmass distribu-tions are derived forevery analysiscategory andwitha nominal valueformH,usingsimulatedeventsfromthedifferentproduction

modes.Thesimulationaccountsforthetrigger,reconstruction,and identification efficiencies, which are measured with data-driven techniques. A weight is applied to the simulated events so that the distributionofthenumberofinteractions perbunch crossing andthelocation oftheprimary vertexarematched tothe distri-butions observed in data.A detaileddescriptionof each ofthese stepscanbefoundinRef. [9].

Since the distribution of mγ γ dependson the correct assign-mentofthevertexassociatedwiththediphotoncandidate,signal models were constructed withcorrect and wrong vertex assign-mentscenariosseparately.Foreachprocess,analysiscategory,and vertexscenario, themγ γ distributionswere fit withasumof,at most,fourGaussianfunctions.

For each process, analysiscategory, andvertex scenario, a si-multaneous fitofthesignalsamplesatmassvaluesrangingfrom 120 to 130 GeV is performed to obtain the variations of the pa-rameters of the Gaussian functions, described by polynomials in

mH,usedinthesignalmodelfit.

Thefinalfitfunctionforeachcategoryisobtainedbysumming thefunctionsforallproductionmodesnormalisedtotheexpected signalyieldsinthatcategory.Fig.3showsthesignalmodel corre-spondingtomH

=

125GeV for thebestresolutioncategory,which

istheuntaggedeventswiththehighestsignal-to-backgroundratio andthe highestdiphotonBDT score,‘Untagged 0’.Alsoshownin the samefigureisthe signalmodelforthe sumof allcategories, with each category weighted by the corresponding S/(S+B) ratio, where S isthe number ofsignal events,and Bis the numberof backgroundeventsinawindowaroundthemHpeak.Inthefigure

the effectivewidth (

σ

eff), definedashalf ofthe smallestinterval

that contains68.3%oftheinvariantmassdistribution,isgiven,as isthefullwidthathalfmaximum(FWHM).

7.2. Backgroundmodel

The model used to describe the background for each of the analysiscategoriesisobtainedfromdatausingthediscrete profil-ing method [19].Inthismethod,alargesetofcandidatefunction families is considered, includingexponential functions, Bernstein polynomials,Laurentseries,andpowerlawfunctions.Thesearefit to themγ γ distribution inthemassrangeof100to 180 GeV.For each familyoffunctions,aFisher test [20] isperformedto deter-minethemaximumordertobeusedinthefit,whiletheminimum orderisdetermined byplacinga requirementon thegoodnessof thefittothedata.Thechoiceofthebackgroundfunctionistreated asadiscrete nuisanceparameterinthefittoaccount forthe un-certaintyassociatedwiththearbitrarychoiceofthefunction. 8. Systematic uncertainties

The systematic uncertainties are treateddifferentlydepending ontheireffectonthediphotoninvariantmassdistributionsinthe differentsignalcategories.Thesystematicuncertaintiesinthe pho-ton energyscaleandresolutionmodifytheshapeofthediphoton massdistributioninthesignalmodel.Othersystematic uncertain-ties,whilenotaffectingthesignalshape,affecttheeventyield.The sourcesofuncertaintyincludedinpreviousCMSH

→

γ γ

analyses aredescribedinRef. [9].Amoreprecisedeterminationofthe sys-tematicuncertaintiesinthephotonenergyscaleandresolutionhas beendevelopedforthepresentanalysisandisdescribedhere.

Fig. 3. Thesignalshapemodelsfor thehighestresolutionanalysiscategory(left), andthesumofallcategories combinedtogetherafterscaling eachofthembythe correspondingS/(S+B)ratio(right)forasimulatedH→γ γ signalsamplewithmH=125GeV.Theopensquaresrepresentweightedsimulatedeventsandtheblueline representsthecorrespondingmodel.Alsoshownaretheσeffvalue(halfthewidthofthenarrowestintervalcontaining68.3%oftheinvariantmassdistribution)andthefull widthathalfmaximum(FWHM).

8.1.Uncertaintiesinthephotonenergyscaleestimatedwithelectrons

Thefollowingsourcesofsystematicuncertaintiesinthephoton energyscalewere first estimatedusing electrons andpropagated tothephotons.

•

Electronenergyscaleandresolution:Theuncertaintyinthe elec-tronenergyscaleandresolutioncorrectionsarederivedusing Z

→

ee eventsby varyingthedistribution of R9,theelectron

selections used in the derivation of the corrections, and the transverseenergythresholdsontheelectronpairsusedinthe derivationofthecorrections.Thisuncertaintyis0.05–0.1%for electrons in the EB, and 0.1–0.3% for electrons in the ECAL endcaps.

•

Residual pTdependenceoftheenergyscalecorrection: Since the

correctionsfortheresidualdifferencesbetweendataand sim-ulation were estimated with Z

→

ee events (



pT



≈

45GeV),

applying them to photons with



pT



≈

60GeV introduces an

additional systematicerror. The degree of nonclosure of the

pT-dependent electron energy scale corrections, as described

inSection5.1,isusedastheestimateofthissourceof uncer-tainty,andisindicatedbythebandlabelledasnonlinearityin Fig. 1.Forelectrons having pT

<

80GeV,corresponding to all

analysiscategoriesexcepttheUntagged0category,this uncer-tainty is0.075%.Forelectronshaving pT greaterthan 80 GeV,

corresponding to the Untagged 0category, the uncertaintyis 0.15%.Thisuncertaintyisappliedconservativelyontheglobal energyscaleandiscorrelatedamongallphotoncandidates.

8.2.Uncertaintiesduetodifferencesbetweenelectronsandphotons

Additional systematicuncertainties dueto the differences be-tweentheresponseofECALtoelectronsandphotonswerestudied andassignedasfollows:

•

Modellingofthematerialbudget: Theuncertainty inthe mate-rialbudgetbetweentheinteractionpointandtheECAL,which affectselectronandphotonshowersdifferently,wasevaluated as described in Ref. [9], andis at most0.24% of the photon energyscale.

•

Nonuniformityofthelightcollection:The showermaximum for photonsisdeeperthanthatofelectronsbyapproximatelyone radiationlength,whichis0.89 cm inleadtungstate.Hencethe

differences inthe light collectionefficiency along the length of the ECAL crystals will introduce a difference in the ECAL response to electrons and photons. To account for this, an additionalsystematicuncertaintyisassignedtothephoton en-ergyscale.Duetotheincreaseintheradiationdamagetothe ECALcrystalsinRun2comparedtoRun1,theimpact ofthe nonuniformityinlight collection efficiencyhasbecome more important.Therefore,a specialefforthasbeenmadetostudy thiseffectandtobetterestimatetheassociatedsystematic un-certaintyinthephotonenergyscale.Thisisestimatedusinga light collection efficiency model derived from a detailed op-ticalsimulation [21] and validatedwithmeasurements made withirradiatedcrystals [22].Thismodeltakesintoaccountthe nonuniformityofthecollectionofscintillationlightdueto ra-diationdamageandthecrystalgeometry.Thisuncertaintyhas been evaluated as a function of pT, supercluster

|

η

SC

|

, and R9 usingthe radiationdamageconditions experiencedin the

2016datatakingperiod.TheresultsaresummarisedinFig.4. Theeffectislessthan0.16%inthebarrelandlessthan0.45% inthe endcap, andaffectsphotonswith R9

>

0.96 themost.

Theuncertaintyisassumedtobecorrelatedamongthe differ-ent

|

η

|

and R9 bins butuncorrelatedbetweenthebarreland

endcapregionsduetothedifferenceinthedegreeofradiation damageandcrystalsize.

•

Mis-modellingoftheinputvariablestotheenergycorrection: The uncertaintyinthephotonenergyscaleduetoimperfect mod-elling of the shower shape in the simulation is found to be negligible(lessthan10 MeV)asaresultofthegoodagreement betweendata andsimulation in the differentinput variables usedinthephotonenergyregressioncorrection.

8.3. Impactofthesourcesofuncertainty

The contribution of each source of the photon energy scale systematic uncertainty to the total uncertainty in the mH

mea-surementwasevaluatedbyperformingalikelihoodscanremoving all but that source and subtracting the statistical uncertainty in quadrature. The results are summarised in Table 1. The leading sourcesofsystematicuncertaintyaffectingmHaretheresidual pT

dependenceofthephotonenergyscale,nonuniformityoflight col-lection, and the electron energy scale and resolution correction.

Table 1

TheobservedimpactofthedifferentuncertaintiesonthemeasurementofmH.

Source Contribution (GeV)

Electron energy scale and resolution corrections 0.10 Residual pTdependence of the photon energy scale 0.11

Modelling of the material budget 0.03

Nonuniformity of the light collection 0.11

Total systematic uncertainty 0.18

Statistical uncertainty 0.18

Total uncertainty 0.26

Fig. 4. Thesystematicuncertaintyduetothedifferencebetweentheelectronand photonenergy scalesfromtheradiationdamage inducednonuniformity oflight collectioninECALcrystals indifferentsupercluster

|

ηSC|and R9 categories.The methodusedtoevaluatethisuncertaintyisdescribedinSection8.2.

The impact of all other sources of systematic uncertainty were foundtobenegligible.

9. Results

To extract the measured value of mH and its uncertainty, a

binned maximum likelihood fit is performed simultaneously to the mγ γ distributions ofthe seven analysis categories described inSec. 6,inthe range100

<

mγ γ

<

180GeV.We usebinned fits toreduce computationtime andabinsizeof0.125 GeV,which is smallcomparedtothediphotonmassresolution.Thedataandthe signal-plus-backgroundmodelfitforthe sumofall analysis cate-goriesisshowninFig.5.

Theexpectednumberofsignaleventsforeachcategoryis sum-marisedinFig.6,wherethecontributionofeachproductionmode to each analysis category is shown. The

σ

eff and

σ

HM are also

listed;thelatteristheFWHM,dividedby2.35.

InthelikelihoodscanofmH,otherparametersofthesignaland

background models are allowed to vary. Systematic uncertainties are includedin theformof nuisanceparameters, andtheresults areobtainedusinganasymptoticapproach [23] withatest statis-ticbased onthe profilelikelihood ratio [24]. In thefit toextract

mH,twoindependentsignalstrengthsforthe(ggH,ttH)

→

γ γ

and

(VBF,VH)

→

γ γ

processesarefreetovary.Thebest-fitmassofmH

isobservedtobemH

=

125.78

±

0.18(stat)

±

0.18(syst) GeV,while

itwasexpectedtohaveastatisticaluncertaintyof

±

0.21 GeV anda systematicuncertaintyof

±

0.18 GeV.Thesignalstrengthsobtained werefoundtobe compatiblewiththesamefromprevious analy-sisinthe diphotondecaychannel [9]. Theexpecteduncertainties inthemeasurementwereobtainedbygeneratinganAsimovdata set [24] from the expected signal from the standard model plus best-fitbackground model.Thedifference betweenthe measured

valuesofmHintheH

→

γ γ

channelinthetwoLHCrunperiods,

Run1 [10] and2016,is



mH

=

1.12

±

0.43GeV.Thecompatibility

ofthesetworesultsisatthelevelof2.6standarddeviations.A de-tailed setofcross-checkswas performedtoensure thatthisshift isstatistical.

9.1. CombinationwiththeH

→

ZZ

→

4massmeasurementinthe 2016andRun1datasets

The results ofthis mass measurement were combinedwith a measurement of the same quantity in the H

→

ZZ

→

4 decay channel withthe2016datasetreportedby CMSinRef. [5] using thesamedatasetwithapreliminarysetofdetectorconditions.

In the combination a possible correlation may exist between electron andphoton energy scales. In the H

→

γ γ

decay chan-nel,thelargestcontributiontotheuncertaintyonthephoton en-ergy scaleis dueto thedifference inthecalorimeterresponse to electrons andphotons, whichisonlyapplied tothe H

→

γ γ

de-caychannel.Otherdifferencesbetweenthetwodecaychannelsin the derivationof theenergyscale correctionsare themuch finer binning in R9 and their pT-dependence in the H

→

γ γ

decay

channel. Additionally the average energy of the electrons in the H

→

ZZ

→

4 decay channel ismuch lower than themost prob-ablephoton energyintheH

→

γ γ

decaychannel. Thuswe treat theuncertainties,residualtotheelectron-photondifference,inthe electronandphotonenergyscalestobeuncorrelatedbetweenthe twochannels.

The combined value of mH measured from the 2016 data

set is observed to be mH

=

125.46

±

0.13(stat)

±

0.10(syst) GeV

with an expectedstatistical uncertaintyof

±

0.16 GeV and an ex-pected systematic uncertainty of

±

0.10 GeV. Three independent signal strengths for the(ggH, ttH)

→

γ γ

, (VBF, VH)

→

γ γ

and pp

→

H

→

ZZ

→

4 processes are free to vary in the fit to ex-tractmH,so that we are not completelydependent on the

stan-dard model fortheproduction anddecayratios. Thisresultis in good agreement with the ATLAS+CMS Run 1 measurement [4],

mH

=

125.09

±

0.24GeV. A scan of the value oftwice the

nega-tivelogarithmofthelikelihood(

−

2ln L)asafunctionofmHfor

thetwoindividualdecaychannels,aswellastheir combinationis showninFig.7.

The same procedure was used to combine this result from the 2016 data set with the same measurement (H

→

γ γ

and H

→

ZZ

→

4) obtainedfrom the Run1 data [25]. The resultof combining the measurements from both data taking periods is

mH

=

125.38

±

0.11(stat)

±

0.08(syst) GeV withan expected

sta-tistical uncertainty of

±

0.13 GeV andan expectedsystematic un-certainty of

±

0.08 GeV. Fig. 8 shows the likelihood scans of the combinedHiggsbosonmassintheH

→

γ γ

andH

→

ZZ

→

4 de-cay channelswiththeRun1and2016datasetsindividually and thesamecombiningthetwodatasets.Asummaryofthe individ-ual and combinedmeasurements with the Run1 and2016 data setsisshowninFig.9.

Fig. 5. Dataandsignal-plus-backgroundmodelfitforallcategoriessummed(left)andwherethecategoriesaresummedweightedbytheircorrespondingsensitivities,given byS/(S+B)(right).Theone(green)andtwo(yellow)standarddeviationbandsincludetheuncertaintiesinthebackgroundcomponentofthefit.Thelowerpanelineachplot showstheresidualsafterthebackgroundsubtraction.

Fig. 6. Theexpectednumberofsignaleventspercategoryandthepercentagebreakdownperproductionmode.Theσeffvalue(halfthewidthofthenarrowestinterval containing68.3%oftheinvariantmassdistribution)isalsoshownasanestimateofthemγ γ resolutioninthatcategoryandcompareddirectlytotheσHM.Theratioofthe numberofsignalevents(S)tothenumberofsignalplusbackgroundevents(S+B)isshownontheright-handpanel.

10. Summary

Inthis Letterwe describe ameasurement of the Higgsboson mass in the diphoton decay channel with 35.9 fb−1 of data col-lectedin2016at

√

s

=

13TeV attheLHC.Newanalysistechniques have been introduced to improve the precision of the measure-mentand we haveused a refined detectorcalibration. The tech-nique that is new with respect to the previous analysis in the diphotondecaychannel [9] istheintroductionofresidualenergy corrections in much finer bins of

η

, pT and the shower shape

variable R9 of the electrons from Z

→

ee decays, in which the

electronshowersare reconstructedasphotons. Wehavealso em-ployedanewmethodto estimatethe systematicuncertaintydue tochanges inthe transparencyofthe crystalsinthe electromag-netic calorimeter withradiation damage. The measured value of

the Higgs boson mass in the diphoton decay channel is found to bemH

=

125.78

±

0.26GeV.This measurementhas been

com-bined with a recent measurement by CMS of the same quan-tity in the H

→

ZZ

→

4 decay channel [5] to obtain a value of

mH

=

125.46

±

0.16GeV.Furthermore,whentheRun2resultwith

the 2016dataset iscombinedwith thesamemeasurement per-formedinRun1at7and8 TeV thevalueoftheHiggsbosonmass isfoundtobemH

=

125.38

±

0.14GeV.Thisiscurrentlythemost

precisemeasurementofthemassoftheHiggsboson. Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technicalandadministrative staffsatCERN andatother CMS

in-Fig. 7. ThelikelihoodscanofthemeasuredHiggsbosonmassintheH→γ γ and H→ZZ→4decaychannelsindividuallyandforthecombinationwiththe2016 dataset.Thesolidlinesareforthefulllikelihoodscanincludingallsystematic un-certainties,whilethedashedlinesdenotethesamewiththestatisticaluncertainty only.

Fig. 8. ThelikelihoodscanofthecombinedHiggsbosonmassintheH→γ γand H→ZZ→4decaychannelswiththe Run1and2016datasetsandthesame combiningthetwodatasets.Thesolidlinesareforthefulllikelihoodscan includ-ingallsystematicuncertainties,whilethedashedlinesdenotethesamewiththe statisticaluncertaintyonly.

stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentresand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythe computinginfrastructureessential to ouranalyses. Finally, we acknowledge the enduring support for the construc-tionandoperation oftheLHCandthe CMSdetectorprovidedby thefollowingfunding agencies:BMBWFandFWF(Austria); FNRS andFWO (Belgium); CNPq,CAPES, FAPERJ, FAPERGS, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIENCIAS (Colombia); MSESand CSF (Croatia); RPF (Cyprus); SENESCYT (Ecuador); MoER, ERC IUT, PUT and ERDF (Estonia); AcademyofFinland,MEC,andHIP(Finland);CEAandCNRS/IN2P3

Fig. 9. AsummaryofthemeasuredHiggsbosonmassinthe H→γ γ andH→ ZZ→4decaychannels,andforthecombinationofthetwoispresentedhere.The statistical(wider,yellow-shadedbands),and total(blackerrorbars)uncertainties areindicated.The(red)verticallineandcorresponding(grey)shadedcolumn in-dicatethecentralvalueandthetotaluncertaintyoftheRun1+2016combined measurement,respectively.

(France); BMBF, DFG, and HGF (Germany); GSRT (Greece); NK-FIA (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy);MSIPandNRF(RepublicofKorea);MES(Latvia);LAS (Lithuania);MOEandUM(Malaysia);BUAP,CINVESTAV,CONACYT, LNS,SEP,andUASLP-FAI(Mexico);MOS(Montenegro);MBIE(New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portu-gal);JINR(Dubna);MON,ROSATOM, RAS,RFBR,andNRCKI (Rus-sia);MESTD(Serbia);SEIDI,CPAN,PCTI,andFEDER(Spain);MoSTR (Sri Lanka); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter,IPST,STAR, andNSTDA(Thailand);TUBITAKandTAEK (Turkey); NASU (Ukraine); STFC (United Kingdom); DOEand NSF (USA).

Individuals have received support from the Marie-Curie pro-gramme and the European Research Council and Horizon 2020 Grant, contract Nos. 675440, 752730, and 765710 (European Union); the Leventis Foundation; the Alfred P. Sloan Founda-tion; the Alexander von Humboldt Foundation; the Belgian Fed-eral 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 Technolo-gie (IWT-Belgium); the F.R.S.-FNRS and FWO (Belgium) under the “Excellence of Science – EOS” – be.h project n. 30820817; the Beijing Municipal Science & Technology Commission, No. Z191100007219010; The Ministryof Education,Youth andSports (MEYS) of the Czech Republic; the Deutsche Forschungsgemein-schaft (DFG) under Germany’s Excellence Strategy – EXC 2121 “Quantum Universe” – 390833306; the Lendület (“Momentum”) ProgrammeandtheJánosBolyaiResearchScholarshipofthe Hun-garian Academy of Sciences, the New National Excellence Pro-gram ÚNKP, the NKFIA research grants 123842, 123959, 124845, 124850, 125105, 128713, 128786, and 129058 (Hungary); the Council of Science and Industrial Research, India; the HOMING PLUSprogramme oftheFoundation forPolishScience,cofinanced from European Union, Regional Development Fund, the Mobility Plus programme of the Ministry of Science and Higher Educa-tion, the National Science Center (Poland), contracts Harmonia 2014/14/M/ST2/00428,Opus2014/13/B/ST2/02543,2014/15/B/ST2/ 03998,and2015/19/B/ST2/02861,Sonata-bis2012/07/E/ST2/01406; the National Priorities Research Program by Qatar National Re-search Fund; the Ministry of Science and Education, grant no. 14.W03.31.0026 (Russia); the ProgramaEstatal de Fomento de la

Investigación CientíficayTécnica de ExcelenciaMaríade Maeztu, grantMDM-2015-0509andtheProgramaSeveroOchoadel Princi-padode Asturias; theThalisandAristeia programmescofinanced byEU-ESFandtheGreekNSRF;theRachadapisekSompotFundfor Postdoctoral Fellowship, Chulalongkorn University and the Chu-lalongkorn Academic into Its 2nd Century Project Advancement Project (Thailand);The Kavli Foundation;the NvidiaCorporation; the SuperMicro Corporation; The Welch Foundation, contract C-1845;andtheWestonHavensFoundation(USA).

Declaration of competing interest

Theauthorsdeclarethattheyhavenoknowncompeting finan-cialinterestsorpersonalrelationshipsthatcouldhaveappearedto influencetheworkreportedinthispaper.

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The CMS Collaboration

A.M. Sirunyan

†

,

A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam,

F. Ambrogi,

T. Bergauer,

M. Dragicevic,

J. Erö,

A. Escalante Del Valle,

M. Flechl,

R. Frühwirth

1

,

M. Jeitler

1

,

N. Krammer,

I. Krätschmer,

D. Liko,

T. Madlener,

I. Mikulec,

N. Rad,

J. Schieck

1

,

R. Schöfbeck,

M. Spanring,

W. Waltenberger,

C.-E. Wulz

1

,

M. Zarucki

InstitutfürHochenergiephysik,Wien,Austria

V. Drugakov,

V. Mossolov,

J. Suarez Gonzalez

InstituteforNuclearProblems,Minsk,Belarus

M.R. Darwish,

E.A. De Wolf,

D. Di Croce,

X. Janssen,

A. Lelek,

M. Pieters,

H. Rejeb Sfar,

H. Van Haevermaet,

P. Van Mechelen,

S. Van Putte,

N. Van Remortel

F. Blekman,

E.S. Bols,

S.S. Chhibra,

J. D’Hondt,

J. De Clercq,

D. Lontkovskyi,

S. Lowette,

I. Marchesini,

S. Moortgat,

Q. Python,

S. Tavernier,

W. Van Doninck,

P. Van Mulders

VrijeUniversiteitBrussel,Brussel,Belgium

D. Beghin,

B. Bilin,

B. Clerbaux,

G. De Lentdecker,

H. Delannoy,

B. Dorney,

L. Favart,

A. Grebenyuk,

A.K. Kalsi,

L. Moureaux,

A. Popov,

N. Postiau,

E. Starling,

L. Thomas,

C. Vander Velde,

P. Vanlaer,

D. Vannerom

UniversitéLibredeBruxelles,Bruxelles,Belgium

T. Cornelis,

D. Dobur,

I. Khvastunov

2

,

M. Niedziela,

C. Roskas,

K. Skovpen,

M. Tytgat,

W. Verbeke,

B. Vermassen,

M. Vit

GhentUniversity,Ghent,Belgium

O. Bondu,

G. Bruno,

C. Caputo,

P. David,

C. Delaere,

M. Delcourt,

A. Giammanco,

V. Lemaitre,

J. Prisciandaro,

A. Saggio,

M. Vidal Marono,

P. Vischia,

J. Zobec

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

G.A. Alves,

G. Correia Silva,

C. Hensel,

A. Moraes

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas,

W. Carvalho,

J. Chinellato

3

,

E. Coelho,

E.M. Da Costa,

G.G. Da Silveira

4

,

D. De Jesus Damiao,

C. De Oliveira Martins,

S. Fonseca De Souza,

L.M. Huertas Guativa,

H. Malbouisson,

J. Martins

5

,

D. Matos Figueiredo,

M. Medina Jaime

6

,

M. Melo De Almeida,

C. Mora Herrera,

L. Mundim,

H. Nogima,

W.L. Prado Da Silva,

P. Rebello Teles,

L.J. Sanchez Rosas,

A. Santoro,

A. Sznajder,

M. Thiel,

E.J. Tonelli Manganote

3

,

F. Torres Da Silva De Araujo,

A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

C.A. Bernardes

a

,

L. Calligaris

a

,

T.R. Fernandez Perez Tomei

a

,

E.M. Gregores

b

,

D.S. Lemos,

P.G. Mercadante

b

,

S.F. Novaes

a

,

Sandra S. Padula

a

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

A. Aleksandrov,

G. Antchev,

R. Hadjiiska,

P. Iaydjiev,

M. Misheva,

M. Rodozov,

M. Shopova,

G. Sultanov

InstituteforNuclearResearchandNuclearEnergy,BulgarianAcademyofSciences,Sofia,Bulgaria

M. Bonchev,

A. Dimitrov,

T. Ivanov,

L. Litov,

B. Pavlov,

P. Petkov,

A. Petrov

UniversityofSofia,Sofia,Bulgaria

W. Fang

7

,

X. Gao

7

,

L. Yuan

BeihangUniversity,Beijing,China

M. Ahmad,

Z. Hu,

Y. Wang

DepartmentofPhysics,TsinghuaUniversity,Beijing,China

G.M. Chen

8

,

H.S. Chen

8

,

M. Chen,

C.H. Jiang,

D. Leggat,

H. Liao,

Z. Liu,

A. Spiezia,

J. Tao,

E. Yazgan,

H. Zhang,

S. Zhang

8

,

J. Zhao

InstituteofHighEnergyPhysics,Beijing,China

A. Agapitos,

Y. Ban,

G. Chen,

A. Levin,

J. Li,

L. Li,

Q. Li,

Y. Mao,

S.J. Qian,

D. Wang,

Q. Wang

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

ZhejiangUniversity,Hangzhou,China

C. Avila,

A. Cabrera,

C. Florez,

C.F. González Hernández,

M.A. Segura Delgado

UniversidaddeLosAndes,Bogota,Colombia

J. Mejia Guisao,

J.D. Ruiz Alvarez,

C.A. Salazar González,

N. Vanegas Arbelaez

UniversidaddeAntioquia,Medellin,Colombia

D. Giljanovi ´c,

N. Godinovic,

D. Lelas,

I. Puljak,

T. Sculac

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,

M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,

D. Ferencek,

K. Kadija,

B. Mesic,

M. Roguljic,

A. Starodumov

9

,

T. Susa

InstituteRudjerBoskovic,Zagreb,Croatia

M.W. Ather,

A. Attikis,

E. Erodotou,

A. Ioannou,

M. Kolosova,

S. Konstantinou,

G. Mavromanolakis,

J. Mousa,

C. Nicolaou,

F. Ptochos,

P.A. Razis,

H. Rykaczewski,

H. Saka,

D. Tsiakkouri

UniversityofCyprus,Nicosia,Cyprus

M. Finger

10

,

M. Finger Jr.

10

,

A. Kveton,

J. Tomsa

CharlesUniversity,Prague,CzechRepublic

E. Ayala

EscuelaPolitecnicaNacional,Quito,Ecuador

E. Carrera Jarrin

UniversidadSanFranciscodeQuito,Quito,Ecuador

H. Abdalla

11

,

S. Elgammal

12

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

S. Bhowmik,

A. Carvalho Antunes De Oliveira,

R.K. Dewanjee,

K. Ehataht,

M. Kadastik,

M. Raidal,

C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,

L. Forthomme,

H. Kirschenmann,

K. Osterberg,

M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

F. Garcia,

J. Havukainen,

J.K. Heikkilä,

V. Karimäki,

M.S. Kim,

R. Kinnunen,

T. Lampén,

K. Lassila-Perini,

S. Laurila,

S. Lehti,

T. Lindén,

H. Siikonen,

E. Tuominen,

J. Tuominiemi

HelsinkiInstituteofPhysics,Helsinki,Finland

P. Luukka,

T. Tuuva

LappeenrantaUniversityofTechnology,Lappeenranta,Finland

M. Besancon,

F. Couderc,

M. Dejardin,

D. Denegri,

B. Fabbro,

J.L. Faure,

F. Ferri,

S. Ganjour,

A. Givernaud,

P. Gras,

G. Hamel de Monchenault,

P. Jarry,

C. Leloup,

B. Lenzi,

E. Locci,

J. Malcles,

J. Rander,

A. Rosowsky,

M.Ö. Sahin,

A. Savoy-Navarro

13

,

M. Titov,

G.B. Yu

S. Ahuja,

C. Amendola,

F. Beaudette,

P. Busson,

C. Charlot,

B. Diab,

G. Falmagne,

R. Granier de Cassagnac,

I. Kucher,

A. Lobanov,

C. Martin Perez,

M. Nguyen,

C. Ochando,

P. Paganini,

J. Rembser,

R. Salerno,

J.B. Sauvan,

Y. Sirois,

A. Zabi,

A. Zghiche

LaboratoireLeprince-Ringuet,CNRS/IN2P3,EcolePolytechnique,InstitutPolytechniquedeParis,France

J.-L. Agram

14

,

J. Andrea,

D. Bloch,

G. Bourgatte,

J.-M. Brom,

E.C. Chabert,

C. Collard,

E. Conte

14

,

J.-C. Fontaine

14

,

D. Gelé,

U. Goerlach,

C. Grimault,

M. Jansová,

A.-C. Le Bihan,

N. Tonon,

P. Van Hove

UniversitédeStrasbourg,CNRS,IPHCUMR7178,Strasbourg,France

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,

C. Bernet,

G. Boudoul,

C. Camen,

A. Carle,

N. Chanon,

R. Chierici,

D. Contardo,

P. Depasse,

H. El Mamouni,

J. Fay,

S. Gascon,

M. Gouzevitch,

B. Ille,

Sa. Jain,

I.B. Laktineh,

H. Lattaud,

A. Lesauvage,

M. Lethuillier,

L. Mirabito,

S. Perries,

V. Sordini,

L. Torterotot,

G. Touquet,

M. Vander Donckt,

S. Viret

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

A. Khvedelidze

10

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze

10

TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann,

L. Feld,

K. Klein,

M. Lipinski,

D. Meuser,

A. Pauls,

M. Preuten,

M.P. Rauch,

J. Schulz,

M. Teroerde

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

M. Erdmann,

B. Fischer,

S. Ghosh,

T. Hebbeker,

K. Hoepfner,

H. Keller,

L. Mastrolorenzo,

M. Merschmeyer,

A. Meyer,

P. Millet,

G. Mocellin,

S. Mondal,

S. Mukherjee,

D. Noll,

A. Novak,

T. Pook,

A. Pozdnyakov,

T. Quast,

M. Radziej,

Y. Rath,

H. Reithler,

J. Roemer,

A. Schmidt,

S.C. Schuler,

A. Sharma,

S. Wiedenbeck,

S. Zaleski

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

G. Flügge,

W. Haj Ahmad

15

,

O. Hlushchenko,

T. Kress,

T. Müller,

A. Nowack,

C. Pistone,

O. Pooth,

D. Roy,

H. Sert,

A. Stahl

16

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin,

P. Asmuss,

I. Babounikau,

H. Bakhshiansohi,

K. Beernaert,

O. Behnke,

A. Bermúdez Martínez,

A.A. Bin Anuar,

K. Borras

17

,

V. Botta,

A. Campbell,

A. Cardini,

P. Connor,

S. Consuegra Rodríguez,

C. Contreras-Campana,

V. Danilov,

A. De Wit,

M.M. Defranchis,

C. Diez Pardos,

D. Domínguez Damiani,

G. Eckerlin,

D. Eckstein,

T. Eichhorn,

A. Elwood,

E. Eren,

E. Gallo

18

,

A. Geiser,

A. Grohsjean,

M. Guthoff,

M. Haranko,

A. Harb,

A. Jafari,

N.Z. Jomhari,

H. Jung,

A. Kasem

17

,

M. Kasemann,

H. Kaveh,

J. Keaveney,

C. Kleinwort,

J. Knolle,

D. Krücker,

W. Lange,

T. Lenz,

J. Lidrych,

K. Lipka,

W. Lohmann

19

,

R. Mankel,

I.-A. Melzer-Pellmann,

A.B. Meyer,

M. Meyer,

M. Missiroli,

J. Mnich,

A. Mussgiller,

V. Myronenko,

D. Pérez Adán,

S.K. Pflitsch,

D. Pitzl,

A. Raspereza,

A. Saibel,

M. Savitskyi,

V. Scheurer,

P. Schütze,

C. Schwanenberger,

R. Shevchenko,

A. Singh,

R.E. Sosa Ricardo,

H. Tholen,

O. Turkot,

A. Vagnerini,

M. Van De Klundert,

R. Walsh,

Y. Wen,

K. Wichmann,

C. Wissing,

O. Zenaiev,

R. Zlebcik

DeutschesElektronen-Synchrotron,Hamburg,Germany

R. Aggleton,

S. Bein,

L. Benato,

A. Benecke,

T. Dreyer,

A. Ebrahimi,

F. Feindt,

A. Fröhlich,

C. Garbers,

R. Kogler,

N. Kovalchuk,

S. Kurz,

V. Kutzner,

J. Lange,

T. Lange,

A. Malara,

J. Multhaup,

C.E.N. Niemeyer,

A. Reimers,

O. Rieger,

P. Schleper,

S. Schumann,

J. Schwandt,

J. Sonneveld,

H. Stadie,

G. Steinbrück,

B. Vormwald,

I. Zoi

UniversityofHamburg,Hamburg,Germany

M. Akbiyik,

M. Baselga,

S. Baur,

T. Berger,

E. Butz,

R. Caspart,

T. Chwalek,

W. De Boer,

A. Dierlamm,

K. El Morabit,

N. Faltermann,

M. Giffels,

A. Gottmann,

F. Hartmann

16

,

C. Heidecker,

U. Husemann,

S. Kudella,

S. Maier,

S. Mitra,

M.U. Mozer,

D. Müller,

Th. Müller,

M. Musich,

A. Nürnberg,

G. Quast,

K. Rabbertz,

D. Schäfer,

M. Schröder,

I. Shvetsov,

H.J. Simonis,

R. Ulrich,

M. Wassmer,

M. Weber,

C. Wöhrmann,

R. Wolf,

S. Wozniewski

KarlsruherInstitutfuerTechnologie,Karlsruhe,Germany

G. Anagnostou,

P. Asenov,

G. Daskalakis,

T. Geralis,

A. Kyriakis,

D. Loukas,

G. Paspalaki

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

M. Diamantopoulou,

G. Karathanasis,

P. Kontaxakis,

A. Manousakis-katsikakis,

A. Panagiotou,

I. Papavergou,

N. Saoulidou,

A. Stakia,

K. Theofilatos,

K. Vellidis,

E. Vourliotis

NationalandKapodistrianUniversityofAthens,Athens,Greece

G. Bakas,

K. Kousouris,

I. Papakrivopoulos,

G. Tsipolitis,

A. Zacharopoulou

NationalTechnicalUniversityofAthens,Athens,Greece

I. Evangelou,

C. Foudas,

P. Gianneios,

P. Katsoulis,

P. Kokkas,

S. Mallios,

K. Manitara,

N. Manthos,

I. Papadopoulos,

J. Strologas,

F.A. Triantis,

D. Tsitsonis

UniversityofIoánnina,Ioánnina,Greece

M. Bartók

20

,

R. Chudasama,

M. Csanad,

P. Major,

K. Mandal,

A. Mehta,

G. Pasztor,

O. Surányi,

G.I. Veres

MTA-ELTELendületCMSParticleandNuclearPhysicsGroup,EötvösLorándUniversity,Budapest,Hungary

G. Bencze,

C. Hajdu,

D. Horvath

21

,

F. Sikler,

V. Veszpremi,

G. Vesztergombi

†

WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni,

S. Czellar,

J. Karancsi

20

,

J. Molnar,

Z. Szillasi

InstituteofNuclearResearchATOMKI,Debrecen,Hungary

P. Raics,

D. Teyssier,

Z.L. Trocsanyi,

B. Ujvari

InstituteofPhysics,UniversityofDebrecen,Debrecen,Hungary

T. Csorgo,

W.J. Metzger,

F. Nemes,

T. Novak

EszterhazyKarolyUniversity,KarolyRobertCampus,Gyongyos,Hungary

S. Choudhury,

J.R. Komaragiri,

P.C. Tiwari

IndianInstituteofScience(IISc),Bangalore,India

S. Bahinipati

22

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C. Kar,

G. Kole,

P. Mal,

V.K. Muraleedharan Nair Bindhu,

A. Nayak

23

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D.K. Sahoo

22

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S.K. Swain

NationalInstituteofScienceEducationandResearch,HBNI,Bhubaneswar,India

S. Bansal,

S.B. Beri,

V. Bhatnagar,

S. Chauhan,

N. Dhingra

24

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R. Gupta,

A. Kaur,

M. Kaur,

S. Kaur,

P. Kumari,

M. Lohan,

M. Meena,

K. Sandeep,

S. Sharma,

J.B. Singh,

A.K. Virdi

A. Bhardwaj,

B.C. Choudhary,

R.B. Garg,

M. Gola,

S. Keshri,

Ashok Kumar,

M. Naimuddin,

P. Priyanka,

K. Ranjan,

Aashaq Shah,

R. Sharma

UniversityofDelhi,Delhi,India

R. Bhardwaj

25

,

M. Bharti

25

,

R. Bhattacharya,

S. Bhattacharya,

U. Bhawandeep

25

,

D. Bhowmik,

S. Dutta,

S. Ghosh,

B. Gomber

26

,

M. Maity

27

,

K. Mondal,

S. Nandan,

A. Purohit,

P.K. Rout,

G. Saha,

S. Sarkar,

T. Sarkar

27

,

M. Sharan,

B. Singh

25

,

S. Thakur

25

SahaInstituteofNuclearPhysics,HBNI,Kolkata,India

P.K. Behera,

S.C. Behera,

P. Kalbhor,

A. Muhammad,

P.R. Pujahari,

A. Sharma,

A.K. Sikdar

IndianInstituteofTechnologyMadras,Madras,India

D. Dutta,

V. Jha,

D.K. Mishra,

P.K. Netrakanti,

L.M. Pant,

P. Shukla

BhabhaAtomicResearchCentre,Mumbai,India

T. Aziz,

M.A. Bhat,

S. Dugad,

G.B. Mohanty,

N. Sur,

RavindraKumar Verma

TataInstituteofFundamentalResearch-A,Mumbai,India

S. Banerjee,

S. Bhattacharya,

S. Chatterjee,

P. Das,

M. Guchait,

S. Karmakar,

S. Kumar,

G. Majumder,

K. Mazumdar,

N. Sahoo,

S. Sawant

TataInstituteofFundamentalResearch-B,Mumbai,India

S. Dube,

B. Kansal,

A. Kapoor,

K. Kothekar,

S. Pandey,

A. Rane,

A. Rastogi,

S. Sharma

IndianInstituteofScienceEducationandResearch(IISER),Pune,India

S. Chenarani,

S.M. Etesami,

M. Khakzad,

M. Mohammadi Najafabadi,

M. Naseri,

F. Rezaei Hosseinabadi

InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran

M. Felcini,

M. Grunewald

UniversityCollegeDublin,Dublin,Ireland

M. Abbrescia

a

,

b

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R. Aly

a

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b

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28

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C. Calabria

a

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b

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A. Colaleo

a

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D. Creanza

a

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c

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L. Cristella

a

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b

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N. De Filippis

a

,

c

,

M. De Palma

a

,

b

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A. Di Florio

a

,

b

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W. Elmetenawee

a

,

b

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L. Fiore

a

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A. Gelmi

a

,

b

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G. Iaselli

a

,

c

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M. Ince

a

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b

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S. Lezki

a

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b

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G. Maggi

a

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c

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M. Maggi

a

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J.A. Merlin

a

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G. Miniello

a

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b

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S. My

a

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b

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S. Nuzzo

a

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b

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A. Pompili

a

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b

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G. Pugliese

a

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c

,

R. Radogna

a

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A. Ranieri

a

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G. Selvaggi

a

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b

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L. Silvestris

a

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F.M. Simone

a

,

b

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R. Venditti

a

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P. Verwilligen

a

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

G. Abbiendi

a

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C. Battilana

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b

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D. Bonacorsi

a

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b

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L. Borgonovi

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b

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S. Braibant-Giacomelli

a

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b

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R. Campanini

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b

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P. Capiluppi

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b

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A. Castro

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b

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F.R. Cavallo

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C. Ciocca

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G. Codispoti

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b

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M. Cuffiani

a

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b

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G.M. Dallavalle

a

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F. Fabbri

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A. Fanfani

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b

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E. Fontanesi

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b

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P. Giacomelli

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C. Grandi

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L. Guiducci

a

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b

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F. Iemmi

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b

_,

_{S. Lo Meo}

a

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29

_,

_{S. Marcellini}

a

_,

_{G. Masetti}

a

_,

_{F.L. Navarria}

a

,

b

_,

_{A. Perrotta}

a

_,

_{F. Primavera}

a

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b

_,

A.M. Rossi

a

,

b

,

T. Rovelli

a

,

b

,

G.P. Siroli

a

,

b

,

N. Tosi

a

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

S. Albergo

a

,

b

,

30

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S. Costa

a

,

b

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A. Di Mattia

a

,

R. Potenza

a

,

b

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A. Tricomi

a

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b

,

30

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C. Tuve

a

,

b

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

G. Barbagli

a

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A. Cassese,

R. Ceccarelli,

V. Ciulli

a

,

b

_,

_{C. Civinini}

a

_,

_{R. D’Alessandro}

a

,

b

_,

_{F. Fiori}

a

_,

_{E. Focardi}

a

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b

_,

G. Latino

a

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b

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P. Lenzi

a

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b

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M. Meschini

a

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S. Paoletti

a

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G. Sguazzoni

a

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L. Viliani

a