EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN) CERN-PH-EP-2012-105 Submitted to: Eur. Phys.J.C Search for a fermiophobic Higgs boson in the diphoton decay channel with the ATLAS detector 2 1 0 2 t The ATLAS Collaboration c O 3 2 ] x Abstract e - p A search for a fermiophobic Higgs boson using diphoton events produced in proton-proton e h collisions at a centre-of-mass energy of √s = 7 TeV is performed using data correspond- [ ing to an integrated luminosity of 4.9 fb−1 collected by the ATLAS experiment at the Large 2 Hadron Collider. A specific benchmark model is considered where all the fermion couplings v 1 to the Higgs boson are set to zero and the bosonic couplings are kept at the Standard 0 Model values (fermiophobic Higgs model). The largest excess with respect to the background- 7 only hypothesis is found at 125.5 GeV, with a local significance of 2.9 standard deviations, 0 . which reduces to 1.6 standard deviations when taking into account the look-elsewhere effect. The 5 0 data excludethe fermiophobic Higgsmodelin the ranges 110.0– 118.0 GeV and 119.5 – 121.0 GeV 2 at95%confidencelevel. 1 : v i X r a Eur. Phys. J. C manuscript No. (will be inserted by the editor) Search for a fermiophobic Higgs boson in the diphoton decay channel with the ATLAS detector The ATLAS Collaboration 1Address(es)of author(s) shouldbegiven March 3, 2013 Abstract AsearchforafermiophobicHiggsbosonus- dition, the partial width of the decay to two photons ing diphoton events produced in proton-proton colli- is enhanced by the suppression of the destructive in- sions at a centre-of-mass energy of √s=7 TeV is per- terference between the W-boson and top-quark loops. formedusingdatacorrespondingtoanintegratedlumi- The resulting cross section times branching ratio for nosity of 4.9 fb−1 collected by the ATLAS experiment fermiophobicHiggsbosonproductionwithdecaytotwo at the Large Hadron Collider. A specific benchmark photons is larger than that of the SM for Higgs boson model is considered where all the fermion couplings to masses (m ) below 125 GeV. Table 1 lists, for several H the Higgs boson are set to zero and the bosonic cou- values of m , the fermiophobic Higgs boson cross sec- H plings are kept at the Standard Model values (fermio- tion multiplied by the decay branching ratio into two phobicHiggsmodel).Thelargestexcesswithrespectto photons.Theratioofthisquantitywithrespecttothat the background-onlyhypothesisis foundat125.5GeV, of the SM Higgs boson and the enhancement of the with a local significance of 2.9 standard deviations, diphotonbranchingratioarealsoshown.Inadditionto which reduces to 1.6 standard deviations when taking theenhanceddiphotondecayrates,therecoilingjetsor intoaccountthelook-elsewhereeffect.Thedataexclude vectorbosonsintheVBForVHproductionmodes,re- the fermiophobic Higgs model in the ranges 110.0 – spectively, imply a high transverse momentum for the 118.0 GeV and 119.5 – 121.0 GeV at 95% confidence Higgs boson that can be exploited as a discriminating level. variableintheanalysis.However,forincreasingm the H diphotondecayratefallsrapidly,makingthesearchless Keywords photon, Higgs boson, fermiophobic sensitive at higher masses in this decay channel. SeveralextensionsoftheStandardModel(SM)have Searches for a fermiophobic Higgs boson have been been proposed in which the Higgs field couplings to performedattheLEPandTevatroncolliders.Thecom- some or all fermion generations are substantially sup- bination of results from the LEP experiments [5] ex- pressed,forexampletwoHiggsdoubletmodelsorHiggs cludes a fermiophobic Higgs boson at 95% confidence tripletmodels[1–4].Afermiophobicbenchmarkmodel, level (CL) for masses below 109 GeV. When includ- in which the Higgs field couplings to all fermions are ing both the WW and γγ decay modes, the Tevatron set to zero while the couplings to bosons are kept at experiments exclude a fermiophobic Higgs boson with theirSMvalues,hasbeenintroducedtoallowageneric masses up to 119 GeV [6,7]. investigation of these scenarios [5]. This letter describes a search for a fermiophobic In such a model, the production of the Higgs bo- Higgsbosonusingdiphotoneventsproducedinproton- son in hadron colliders and its decay properties are proton collisions at a centre-of-mass energy of √s = significantly altered compared to the SM. Fermiopho- 7 TeV using data corresponding to an integratedlumi- bic Higgs bosons can only be produced via vector bo- nosity of 4.9 fb−1 collected by the ATLAS experiment. son fusion (VBF) or associated production with vector This analysis follows exactly that of the related search bosons (VH, V = W,Z). Because Higgs boson decays for a SM Higgs boson with the same dataset [8], but to fermionsareabsentattree level,the branchingfrac- the fermiophobic Higgs hypothesis is used to construct tions for decays to gauge bosons are enhanced. In ad- the signal model. The sensitivity to the fermiophobic 2 Table 1: Higgs boson production cross section multi- tracks, where the transverse momentum of each track plied by the branching ratio into two photons for the isrequiredtobelargerthan0.4GeV.Atleasttwopho- fermiophobic benchmark model (σf), the ratio of this tons within the fiducial region η < 2.37 (excluding | | value to the SM value (σf/σSM) and the two pho- the transition region between the barrel and the end- ton branching ratio enhancement compared to the SM cap, 1.37 < η < 1.52) satisfying tight identification | | ( f/ SM)forvariousfermiophobicHiggsbosonmasses. criteria based on electromagnetic shower shapes [11] B B The expected number of signal events after candidate are required. The transverse momenta for the leading selection are also shown for 4.9 fb−1 of data as well as and sub-leading photons are requiredto be largerthan the overallsignal selection efficiencies. 40 GeV and 25 GeV, respectively. The photon recon- struction and identification efficiency ranges typically from 65% to 95% for E in the range between 25 GeV T mH [GeV] 110 115 120 125 130 135 140 145 150 and 80 GeV. The transverse energy deposited around σf [fb] 163 90 53 32 21 13 8.9 5.9 3.9 eachphotonwithinaconeof∆R=q(∆η)2+(∆φ)2 = σf/σSM 3.7 2.1 1.2 0.8 0.6 0.4 0.3 0.3 0.2 0.4, excluding the deposits of the photon itself, is re- quiredto be less than 5 GeV. Correctionsfor the small Bf/BSM 30.2 17.0 10.3 6.7 4.7 3.5 2.8 2.3 2.0 estimated energy leakage outside the excluded region, Signalevents 255 149 91 58 38 25 17 12 7.9 theunderlyingeventandeffectsofadditionalminimum Efficiency[%] 32 34 35 37 38 38 39 40 42 bias interactions occuring in the same or neighbouring bunchcrossings(in-timeandout-of-timepileup)areap- plied to this quantity on an event-by-eventbasis. Theinvariantmassofeachdiphotoncandidate(m ) γγ signal is larger than that for the SM Higgs due to the isevaluatedusingthephotonenergies,theimpactpoints larger diphoton transverse momentum. measuredinthecalorimeterandtheproductionvertex. TheATLASdetectorisdescribedindetailinRef.[9]. The photon energy calibration is performed indepen- The most relevant subsystems for this analysis are the dently for converted and unconverted photons. Con- calorimeter, in particular the electromagnetic section, verted photons are defined to be those with a well- and the inner detector. The electromagnetic calorime- reconstructed conversion vertex in the inner detector. ter is a lead–liquid-argon detector, finely segmented A detailed simulation of the detector geometry and re- in the lateral and longitudinal directions. It is com- sponse is used for the calibration. Additional correc- posedofabarrelpartcoveringthepseudorapidityrange tions due to mis-modelling of the material in front of η < 1.475 and two end-cap sections covering 1.375 < the calorimeterandofcalorimeternon-uniformities are | | η < 3.2. The barrel (η < 0.8) and extended barrel applied.Theseamounttoabout 1%dependingonthe | | | | (0.8< η <1.7) hadron calorimeter sections consist of ± pseudorapidity of the photon and are obtained from | | steel and scintillating tiles, while the end-cap sections studies of Z e+e− decays in data [12]. The dipho- (1.5 < η < 3.2) are composed of copper and liquid → ton production vertex along the beam axis is deter- | | argon. The inner detector includes silicon-based pixel mined by combining the trajectories of each photon, and micro-strip detectors in the range η < 2.5, and a measured using the longitudinal segmentation of the | | transition radiationtrackerwith electron identification calorimeter, with a constraint from the average beam capability extending out to η < 2.0. It is surrounded spot position. The position of the conversion vertex is | | byasuperconductingsolenoidthatprovidesa2Taxial also used where the photons convert in the tracking magnetic field. region instrumented with silicon detectors. Conversion Data used in this analysis were recorded using a candidateswithtracksreconstructedininactiveregions diphotontriggerwitha20GeVtransverseenergy(ET) of the innermost pixel layer are rejected to reduce the threshold on each photon. This trigger is seeded by contamination from misidentified electrons. The reso- a first-level trigger, which requires two clusters in the lution of the diphoton mass reconstructed using this electromagneticcalorimeterwithET >14GeVorET > method is dominated by the photon energy resolution. 12GeV,dependingonthedata-takingperiod.Thistrig- Atotalof22,489eventswereselectedwitha dipho- ger has a signal efficiency close to 99% following the toninvariantmassbetween100GeVand160GeV. Al- final event selection. After application of data-quality thoughnotuseddirectlyinthefinalresult,thediphoton requirements the analysed data sample corresponds to samplecompositionwasstudiedusingatwo-dimensional a total integrated luminosity of 4.9 0.2 fb−1 [10]. side-bandtechniquebasedonphotonidentificationqual- ± The events are required to have at least one recon- ityandisolation[8].Thefractionoftruediphotonevents structed vertex with a minimum of three associated was estimated to be (71 5)%. The rest of the back- ± 3 ground is due to events with one or more misidenti- nisation, while PYTHIA is chosen for the VH processes. fiedjets,exceptfor asmall( 0.7%)contributionfrom PileupeffectsaresimulatedbyoverlayingeachMCevent ∼ Drell-Yan events where both electrons pass the photon with a variable number of simulated inelastic pp colli- selection. sions, taking into account the LHC bunch-train struc- To enhance the sensitivity of the analysis, the data ture [26]. sample is split into nine categories, each with differ- Asetofcorrectionsisappliedtothesimulatedevents ent expected signal mass resolutions, signal yields and in orderto matchthe data-taking conditions.The sim- signal-to-background ratios (S/B). This categorisation ulated events are re-weighted to reproduce the distri- depends on the impact point of the photons on the butionoftheaveragenumberofinteractionsperbunch calorimeter,thepresenceofphotonconversionsandthe crossing reconstructed in the data, which has a mean value of the component of the diphoton transversemo- value of about nine for the data sample used in this mentum orthogonal to the diphoton thrust-like axis in analysis.Theenergiesofthesimulatedphotonsaresmeared the transverse plane1 (p ) [13,14]. to account for differences observed in studies of the Tt Events in which both photons are unconverted are calorimeterresolutionwithZ e+e−decays.Calorime- → separated into the unconverted central (both photons ter shower shapes used in the photon identification are in the central region of the barrel calorimeter, η < slightly shifted to improve the agreement with the dis- | | 0.75)andunconvertedrest (allotherevents)categories. tributions observed with inclusive photons from data. Events for which at least one photon is converted are ThenumberoffermiophobicHiggsbosonsexpected separatedintotheconvertedcentral (bothphotonswithin aftercandidateselectionandtheoverallsignalselection η < 0.75), converted transition (at least one photon efficiencyforvariousvaluesofm areshowninTable1. H | | close to the barrel/end-cap transition region, 1.3 < The signal selection efficiency increases from 32% to η < 1.75) and converted rest (the remaining events) 42% as the Higgs boson mass increases from 110 GeV | | categories. to 150 GeV. With the exception of the converted transition cat- egory,alltheeventsarefurthersubdividedintolow pTt Table 2: Expected signal mass resolution (σCB and (pTt < 40 GeV) and high pTt (all other events) cate- FWHM in GeV, see text) and total number of sig- gories.MonteCarlo(MC)simulationstudiesshowthat nal events (N ) for m = 120 GeV for each of the S H afermiophobicHiggsbosonsignalhaslargerpTt onav- nine analysiscategoriesandfor the inclusivecase.Also eragethanbackgroundevents.Thisquantityisstrongly shown for each category are the number of observed correlatedwiththediphotontransversemomentumbut events (N ) in the diphoton mass range from 100GeV D offers several advantages. Higher values of pTt do not to160GeV,andthe expectedsignal-to-backgroundra- includekinematicconfigurationsforwhichthetwopho- tio (S/B) in a mass window containing 90% of the sig- tons are back-to-backin the azimuthal plane with sub- nal. stantially different transverse momenta. This reduces biasesontheidentificationandisolation(transverseen- ergy deposited around the photon) of the sub-leading Category σCB FWHM NS ND S/B photon in the high p categories and retains a mono- Tt tonically falling diphoton invariant mass distribution Unconverted central,lowpTt 1.4 3.3 6.2 1763 0.03 forthebackgroundeventsatthechosencutvalues.The Unconverted central,highpTt1.3 3.2 8.6 235 0.37 latterqualityisadvantageousforthe backgroundmod- Unconverted rest,lowpTt 1.7 3.9 12.1 6234 0.02 elling and associated uncertainties discussed below. Unconverted rest,highpTt 1.6 3.8 16.0 1006 0.13 AfullGeant4-based[15]MCsimulation[16]ofHiggs Converted central,lowpTt 1.6 3.8 4.0 1318 0.02 bosoneventsdecayingintotwophotonsisusedtomodel Converted central,highpTt 1.5 3.5 5.8 184 0.26 the expected signal. The signal yields are normalised Converted rest,lowpTt 2.0 4.6 11.8 7311 0.01 to next-to-next-to-leading-order production cross sec- Converted rest,highpTt 1.9 4.4 16.1 1072 0.09 tions [17–22] and the branching ratios for the fermio- Converted transition 2.3 5.8 10.8 3366 0.01 phobic Higgs boson are calculated using HDECAY [23]. Allcategories 1.7 3.9 91.2 22489 0.03 HiggsbosonVBFproductionissimulatedusingPOWHEG[24] interfaced with PYTHIA [25] for showering and hadro- 1pTt =|pγTγ×t|,wheret= |ppγTγT11−−ppγTγT22| denotesthetransverse The signal is modelled as the sum of a core compo- thrust, pγ1 andbpγ2 arebthe transverse momenta of the two photons,Tand pγγT=pγ1 +pγ2 is the transverse momentum nent, described by a Crystal Ball (CB) function [27], T T T of thediphoton system. and a wider Gaussian component incorporating outly- 4 ingevents.Thelattercomponenttypicallyaccountsfor 800 lwesidstthh-aant-5h%alfo-fmtahxeismigunmal.(FTWabHleM2)lisatnsdthGeaeuxspseiacntedwifdutllh- ents / GeV 670000 ATLAS Low pTt cateDBgoaarctiaek sg2 r0+o1 uc1onndv merotedde ltransition of the core component (σ ) for eachof the nine event Ev Fermiophobic Higgs boson CB m = 120 GeV (MC) 500 H categories. The expected number of signal events for ∫ 400 s = 7 TeV, Ldt = 4.9 fb-1 m = 120 GeV, the number of background events in H the diphoton mass range of 100 GeV to 160 GeV, and 300 the signal-to-background ratio in a mass window con- 200 taining90%ofthesignalarealsoshown.Themainsen- 100 sitivity to the fermiophobic production modes comes g 1010000 110 120 130 140 150 160 sfrigonmaltyhieeldhsigahndpTstigncaatl-etgoo-rbiaecskdgruoeuntodrtahteiiors.eFnhigaunrceed1 Data - Bk -55000 shows the signal diphoton mass distribution summed -100 100 110 120 130 140 150 160 over the high pTt categories for a Higgs boson mass of mγγ [GeV] (a) 120 GeV. 120 / 0.5 GeVN/dmγγ 00..000.681 FmAeTHrm L=Ai o1Sp2h0so iGbmiecuV lHat→ioγnγ FσCWB H=M 1 .=6 3G.7e VGeV Events / GeV 1680000 ATLAS High pTt cateDBmFgeaaHor ctr=maike gi21sor02po10hu1 onGsbd ei =cmV 7 Ho( MdiTgeeCglVs), b∫o sLodnt = 4.9 fb-1 d N 40 1/ 0.04 High p categories Tt 20 0.02 g 410000 110 120 130 140 150 160 Bk 20 1000 105 110 115 120 125 130 135 140 Data - -200 mγγ [GeV] -40 100 110 120 130 140 150 160 mγγ [GeV] Fig. 1: Diphoton invariant mass spectrum from sim- (b) ulated signal samples (dots) with m = 120 GeV H Fig. 2:Diphoton invariantmass spectra for the (a) low summed over the high p categories, superimposed Tt and (b) high p categories, overlaid with the sum of with the signal model (line). Tt thebackground-onlyfitsfromtheindividualcategories. The bottom plots show the residual of the data with respecttothefittedbackground.Thesignalexpectation The observed diphoton invariant mass distribution forafermiophobicHiggsbosonwithamassof120GeV in each category is modelled by an exponential func- superimposed on the background fit is also shown. tion. A fit to the data is performed for which the slope andnormalisationareunconstrained.Studieswithlarge samples of simulated diphoton events show that this simplefunctiongivesagooddescriptionoftheexpected ofthe photonreconstructionandidentificationefficien- shape. The small systematic uncertainties associated cies, which is estimated to be 11%. This uncertainty ± with this assumption are discussed below. Figures 2(a) is studied with electrons from W and Z boson decays and 2(b) show the diphoton mass distributions of the indata,andphotonsfromradiativedecaysofZ bosons selecteddataeventssummedoverthe lowandhighp to electron and muon pairs. In addition, the effect of Tt categories, respectively. The converted transition cate- pileup on photon identification gives a further contri- gory is included in the low p categories. bution to the signal yield uncertainty of 4%. Uncer- Tt ± Systematic uncertainties affecting the signal signif- taintiesrelatedtothetriggerefficiency( 1%),isolation ± icance arise from uncertainties on the predicted signal cut efficiency ( 5%) and luminosity ( 3.9%) are also ± ± yields, the expected partition of the signal among the included here. categories and the modelling of the signal and back- Uncertainties on the signal cross section include a groundshapes.Thedominantexperimentaluncertainty combinationoftheuncertaintiesonthepartondistribu- on the signal yield is due to the imperfect knowledge tion functions [28,29] and α , and uncertainties on the s 5 QCD scale. Combining the VBF and VH production groundmodellinguncertaintyinthehighp categories Tt modes this uncertainty is within 4% over the con- is equivalentto upto 5%ofthe signalyieldwith nomi- ± sidered mass range. To this uncertainty, that due to nalsignalstrength.The estimationofthe uncertainties the H γγ branching ratio ( 5%) is added linearly, is cross-checkedby fitting the data with different func- → ± basedontheSMcalculation[22].Thisyieldsuncertain- tional forms and comparing the result to the exponen- tiesof 9%onthetheoreticalsignalyield,leadingtoan tial fit. ± overall uncertainty of 16% on the total signal expec- The possible presence of a signal is investigated us- ± tation.Inaddition, the uncertainty onthe Higgs boson ingacombinedlikelihoodfunctionconstructedfromthe pT modelling is estimatedbycomparingsignalsamples signal and background models for the diphoton invari- from alternative MC generators– HERWIG[30] for VBF antmassdistributionineachoftheninecategories.Un- andResBos[31]forVH.Theresultisa 1%signalmi- binned maximum likelihood fits of the signal strength ± grationbetweenthe lowandhighpTt categorieswitha are performed, treating the systematic uncertainties as negligible effect on the signal selection efficiency. nuisanceparameters–fourteenintotal.Thesenuisance The dominant uncertainties on the signal mass res- parameters are added to the signal likelihood function olution are due to the uncertainty on the calorime- using a Gaussian term for the background modelling ter energy resolution ( 12%) and photon calibration uncertainty, and log-normal terms for all other uncer- ± ( 6%), which are both extrapolated from the uncer- tainties. ± tainty on the electron calibration determined using Z and J/ψ data [12]. The latter comes from the imper- fect knowledge of the material in front of the active p0 1 al part of the calorimeter and is estimated using simula- oc 1σ L 10-1 tions with different amounts of material.This quantity also affects the fraction of expected events in the cate- 2σ 10-2 Fermiophobic H → γγ gories with converted photons; the maximal migration ATLAS ∫ 2011 data L dt = 4.9 fb-1 between converted and unconverted categories is esti- 10-3 3σ mated to be 4.5%. Other effects on the signal mass Observed p (all categories) ± Obs. p (with0 energy scale uncertainty) resolution are due to pileup fluctuations contributing 0 Obs. p (High p categories) to the cluster energy measurement ( 3%) and to the 10-4 Obs. p00 (Low pTTt t+ Conv. transition) ± Expected p0 with signal (all categories) uncertainty on the photon angular resolution ( 1%) which is studied in Z e+e− decays using the t±rack- 110 115 120 125 130 135 140 145 150 → mH [GeV] baseddirectionmeasurement.The totalrelative uncer- taintyonthediphotoninvariantmassresolutionisthus Fig. 3: Local observed p as a function of the Higgs 0 14%. bosonmassm (solidline)andthemedianexpectation ± H Systematic uncertainties on the background mod- for a fermiophobic signal with the given mH (dotted ellingarisefromapossibledeviationofthebackground line). The five points near 125 GeV show the observed massdistributionfromthe assumedexponentialshape. p0 when the uncertainty on the photon energy scale This uncertainty is evaluated as the number of events is considered. The individual contributions of the low that could be mistakenly attributed to the signal. It is pTt and high pTt categories to the observedp0 are also estimatedfromthe adequacyofthe chosenbackground shown. model’s description of the mass distribution predicted by ResBos [32]. The residuals of the fit of the back- groundmodeltotheResBosdiphotonmassdistribution Thecompatibilityofthedatawiththe background- areintegratedoveraslidingmasswindowof4GeV,the onlyhypothesis,relativetothehypothesisofbackground approximateFWHMoftheexpectedsignal.Thelargest plusthefermiophobicmodelsignal,isquantifiedbythe deviations were found at small invariant masses and local significance p . Figure 3 shows the result for m 0 H theseuncertaintiesarethenappliedoverthewholemass ranging from 110 GeV to 150 GeV, where p is com- 0 range. The resulting uncertainties range from 0.1 to putedin 0.5GeVsteps using asymptoticformulae[33]. ± 7.9eventsintheindividualanalysiscategories,where The contributions to p values from the high p and 0 Tt ± themagnitudeoftheseuncertaintiesisroughlypropor- low p categories are shown separately. The high p Tt Tt tionaltothenumberofbackgroundeventsineachcate- contribution has a minimum p at 125 GeV, while the 0 gory.Theseabsoluteuncertaintiesdonotscalewiththe low p contribution has a minimum at 127 GeV. The Tt signal strength in the final likelihood fit. For a fermio- larger signal-to-background ratio as well as the larger phobic Higgs boson with m = 120 GeV the back- expectedsignalyieldinthehighp categorycompared H Tt 6 tothelowp categoryresultsinthehighp contribu- Tt Tt σ f Observed CL limit ftadoieomrvnaiiandtfioemiomrnumismni.oaTpatithhnoe1gb2fii5incg.5utHhrGeiegeafigVlsnsaocbloosrrhserooesnwusplsstoi.tgnThndehainelp,g0caotvsomaal3bu.fi0eunnesetdxcatppnieo0dcnhateraoddsf σ/CL limit on 10 ±±E x12pσσected CLAss TliLmAitS % Higgs boson mass. 5 9 To obtain the final result, the impact of the un- 1 certainties on the photon energy scale is consideredfor Data 2011, s = 7 TeV ∫ Higgsbosonmassesintheregionoftheminimump0,as Ldt = 4.9 fb-1 shown in Fig. 3. The corresponding effect on the mea- Fermiophobic H → γγ sured p0 value is estimated using pseudo-experiments, 10-1110 115 120 125 130 135 140 145 150 since asymptotic formulae were found not to yield ac- m [GeV] curate estimates of the probability in this case. The H position of the minimum p is almost unchanged and 0 Fig.4:Observed(solidline)andexpected(dottedline) the significance is lowered to 2.9 standard deviations. 95% CL exclusion limits for a fermiophobic Higgs bo- Taking the look-elsewhere effect [34] into account in son normalised to the fermiophobic cross section times the range 110 – 150 GeV, the significance reduces to branching ratio expectation (σ ) as a function of the f about 1.6 standard deviations, with p 0.051. This 0 ≈ Higgs boson mass hypothesis (mH). may be compared to the result of a search for the SM Higgsbosonperformedwiththesamedatasetandcan- didate selection [8], yielding a minimum p at a mass and JSPS, Japan; CNRST, Morocco; FOM and NWO, 0 of 126.5GeV with a global significance of 1.5 standard Netherlands;RCN,Norway;MNiSW,Poland;GRICES deviations.No statisticallysignificantpreferenceforei- andFCT,Portugal;MERYS(MECTS),Romania;MES ther the SM or fermiophobic Higgs boson is observed. of Russia and ROSATOM, Russian Federation; JINR; Giventhelackofevidenceforasignal,mass-dependent MSTD, Serbia; MSSR, Slovakia; ARRS and MVZT, exclusion limits on the fermiophobic benchmark model Slovenia; DST/NRF, South Africa; MICINN, Spain; are calculated at the 95% confidence level (CL) with a SRC and Wallenberg Foundation, Sweden; SER, SNSF profilelikelihoodratioteststatisticintheCL modified and Cantons of Bern and Geneva, Switzerland; NSC, s frequentistapproach[33,35,36]andareshowninFig.4. Taiwan; TAEK, Turkey; STFC, the Royal Society and Fermiophobic Higgs boson masses from 110.0 GeV to Leverhulme Trust, United Kingdom; DOE and NSF, 118.0 GeV and from 119.5 GeV to 121.0 GeV are ex- United States of America. cluded,whiletheexpectedexclusionmassrangeis110.0 ThecrucialcomputingsupportfromallWLCGpart- – 123.5 GeV. These results give more stringent lower nersisacknowledgedgratefully,inparticularfromCERN mass limits than the previous results from LEP andtheATLASTier-1facilitiesatTRIUMF(Canada), (108.2GeV) [5]andthe Tevatron(112.9GeVfromD0, NDGF(Denmark,Norway,Sweden),CC-IN2P3(France), 114GeVfromCDF)[6,37]inthediphotondecaychan- KIT/GridKA(Germany),INFN-CNAF (Italy),NL-T1 nel. (Netherlands),PIC(Spain),ASGC(Taiwan),RAL(UK) and BNL (USA) and in the Tier-2 facilities worldwide. We thank CERN for the very successful operation of the LHC, as well as the support staff from our insti- tutions without whom ATLAS could not be operated References efficiently. 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