Higgs boson production and decay at the LHC is described, together with
related ATLAS search channels, in order to provide an overview of the ATLAS
Higgs discovery potential.Comment: 6 page

Collins-Tooth, Christopher

English

arXiv

Higgs boson production and decay at the LHC is described, together with related ATLAS search channels, in order to provide an overview of the ATLAS Higgs discovery potential.Higgs boson production and decay at the LHC is described, together with related ATLAS search channels, in order to provide an overview of the ATLAS Higgs discovery potential

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arXiv:0712.1509v1  [hep-ex]  10 Dec 2007THE HIGGS DISCOVERY POTENTIAL OFATLASCHRISTOPHER COLLINS-TOOTHforthe ATLAS collaborationDepartm entofPhysicsand Astronom y,University ofGlasgow,Glasgow G12 8QQ,Scotland.October2,2007Higgsboson production and decay atthe LHC isdescribed,togetherwith re-lated ATLAS search channels,in ordertoprovidean overview oftheATLAS Higgsdiscovery potential.1 IntroductionTheATLAS detector[1]isoneoftwogeneralpurposedetectorsunderconstructionattheLargeHadron Collider(LHC),CERN,Switzerland.TheLHC willbegin toprovide ATLAS with colliding beam s,each of7 TeV protons,in the Sum m er of2008.Itisexpected thata low-lum inosity running phase willcom m ence in 2009,with instantaneouslum inosity (L)of1  2cm   2s  1.Theaim ofthisphasewillbeto gatherapproxim ately 30 fb  1 ofintegrated lum inosity (RLdt)by 2011. Afterthis,L willbeincreased toapproxim ately1034 cm   2s  1,with theaim ofgatheringRLdt  300 fb  1 by 2014/2015.TheATLAS triggerwillreducethefrequency ofeventssaved foroineanalysisto approxim ately  200 Hz.Som e im portant design features ofATLAS are its high herm eticity (vitalinm easurem ents ofm issing transverse energy),powerfultracking in the Inner De-tector(usefulforexam ple,in b-tagging m easurem ents),excellentElectrom agneticCalorim eterenergy and angularresolution (e.g. form easurem entof; e ener-gies,and separation of/jet& / 0). ATLAS isalso designed to have excellentm uon detection eciency and m om entum m easurem ent,using theInnerDetectorand the M uon Spectrom eter. The nom inalenergy scales are e=  0:1% ; 0:1% ;jets 1% .12 Standard M odelH iggsproduction and decay atthe LH CFigure 1 shows that by far the m ost im portant production m echanism over theentire m asssearch region fora Standard M odel(SM )Higgsboson isgluon-gluonfusion.Thisproduction m echanism isfollowed in im portanceby VectorBoson Fu-sion (VBF)atthe10  20% level,and Z/W -associated& associated-top productionata stilllowercross-section.Figure1: SM Higgsproduction (left)[2]and decay (right)[3]atthe LHC.The branching ratiosfor SM Higgsdecay are also shown in Figure 1. In theHiggsm assregion M h < 125 G eV,the prim ary decay m echanism ish ! bb,Athigherm asses,decaysto (initially o-shell)gaugebosonsbecom edom inant.Thisoccurs rst for W -bosons,and this decay stays dom inant over the decay to Z-bosons,though the latterispreferred athigherm asses(M h > 2M Z ),because ithasa very clean experim entalsignature.3 AT LA S H iggs sensitivity and searches3.1 AT LA S SM H iggs sensitivityATLAS is optim ised to cover a large spectrum ofpossible Higgs particles andtheirsignatures. The ATLAS SM Higgssignicancesforthe individualchannelsas a function ofM h are shown in Figure 2,and also shown is the overallsig-nicance when m ultiple channels are considered. ATLAS should m ake a lightHiggsdiscovery (M h < 180 G eV)withRLdt= 30 fb  1. Discovery in the regionM h < 120 G eV isclearly the m ostchallenging forATLAS,and willprobably re-quire severalchannels to be com bined. G iven a favourable Higgs m ass,ATLAScould m ake a discovery with m uch lesslum inosity. By com bining VBF,h ! ,tth ! bb & ZZ ,discovery ofa Higgswith M h > 120 G eV could be m ade with2Figure 2: ATLAS sensitivity to thediscovery of a SM Higgs boson forRLdt = 30 fb  1 [4]. No K -factorshavebeen applied.Figure 3: Reconstructed M h for aninput M h = 120 G eV before (top)and after(bottom )background sub-traction (RLdt= 30 fb  1)[5].just10 fb  1 oflum inosity [4]. Above M h > 2M Z ,two on-shellZ-bosonscan becreated,opening up the ‘gold plated’channelh ! ZZ ! 4l .3.2 h ! This channelfeatures a narrow m ass peak over a sm ooth background, but ascan be seen from Figure 2,it is only usefulat low M h (< 140 G eV).This is abenchm ark channelfor ATLAS detector perform ance,relying upon Electrom ag-neticCalorim eterresolution,butalsoaccurateprim ary vertex determ ination.Theirreduciblebackground to thischannelisthe continuum .Powerfulrejection isneeded to reducejet-jet& -jetbackgrounds,wherethejetcould bem isidentiedasa photon.W hen theanalysisisperform ed using NLO production cross-sections[5],the ATLAS signicance varies from 5.4 (M h = 140 G eV),through to 6.2(M h = 130 G eV)and 6.1 (M h = 120 G eV)for30 fb  1 ofintegrated lum inosity.Figure 3 shows a m ass distribution for an assum ed M h = 120 G eV.The analy-sism akesuse ofphoton conversion recovery,where forthe approxim ately 40% ofsignaleventswhereatleastonephoton converts,an 80% recoveryrateisassum ed.3.3 h ! ZZ  ! 4lThischannelhasa clean signature,butlow statistics(3  11 fb forM h = 130 200 G eV)[6].Itisanotherbenchm ark channelfordetectorperform ance,with theappearance offour high transverse m om entum (PT ) charged leptons testing theATLAS m om entum and energy resolution (via the Inner Detector,M uon Spec-trom eterand Electrom agneticCalorim eter).M asspeakscan be produced in this3channele.g. for 4e; 4; 2e2 nalstates, which dier by resolution,but aretypically in the range1:5  2 G eV.The channelalso providesa possibility ofde-term ining the spin and CP-eigenvalue ofa SM Higgs[7]. The m ain backgroundsto the channelare the irreducible ZZ  ! 4l continuum ,and the (reducible)tt! 4l+ X & Zbb ! 4l+ X . These backgroundscontain non-isolated leptonswith high im pact param eters. O nce selection is perform ed,the ZZ-continuumbackground isdom inant.The shape and norm alisation ofthese backgroundswillbe obtained experim entally from data in order to m inim ise PDF and lum inos-ity uncertainties. The ATLAS signalsignicance with no K -factors applied (forRLdt= 30fb  1)risesabove5atM h  130G eV,and increasestoapproxim ately9atM h  150 G eV.Thesignicancethen dropsbelow 5atM h  160 G eV [6].3.4 Vector B oson Fusion h ! W W ( )In addition to being thesecond m ostim portantSM Higgsproduction m echanismaftergluon-gluon fusion,VBF hasa num beroftopologicalfeatureswhich enableATLAS toecientlyrejectbackground.Duetothis,theVBF channelh ! W W ( )in particulardem onstrateslarge discovery potentialoverthe region 125 < M h <190G eV.VBF producesHiggsdecay productswhich liebetween twoforward jets.These jets,with Higgs decay products located between them in pseudorapidity(),coupled with an absence ofjets in the centralregion (due to the absence ofquark-quarkcolourexchange)providetheexperim entalsignatureofVBF.Thetwoforward ‘tagjets’typically havehigherinvariantdijetm ass(M jj)than thetagjetsidentied in Q CD background processes,and so a cuton M jj isalso applied byATLAS to im provebackground rejection.In theh ! W W  ! ll channel,theleptonsarespin-correlated to theHiggsresonance. For a SM Higgs boson,the charged leptons willem erge in the sam edirection as each other. This is yet another topologicalfeature which im provesbackground rejection.Dueto theproduction oftwo neutrinos,only thetransversem ass,M T =p((E llT + ET )2   (pllT + pm issT )2)can bereconstructed.Thisdistri-bution forsignalhaving M h = 160 in theenalstateisshown in Figure 4,alongwith the relevantbackground distributions.W ithRLdt= 10fb  1,theATLAS signalsignicanceatM h = 160G eV forthell nalstatereachesapproxim ately 8:1fortheechannel,and approxim ately7:4 in the ee= channel. The ljj nalstate is also considered by ATLAS,and providesa signicance of4:6 atM h = 160 G eV forRLdt= 30 fb  1. W ithRLdt= 10 fb  1,theATLAS signalsignicanceforthecom bination ofconsideredll & ljj channelsisabove5 for135< M h < 190 G eV [4].3.5 tth (h ! bb)This channelis attractive prim arily due to the large branching ratio ofH ! bbat M h < 130 G eV (see Figure 1). It is also relatively sim ple to trigger ifoneconsidersthe sem i-leptonic nalstate tth ! ljjbbbb,which providesa high-PTisolated lepton and m issing transverseenergy,togetherwith fourb-jets.Thechan-nelhasa com plex nalstate,and thusthere isa large com binatoric background4Figure 4: Distribution ofthe trans-versem assM T fora SM Higgsbosonm assof160G eV in theh ! W W  !ll (e) channelafter allselectioncutsareapplied [4].Figure 5: M ass distribution for thetth (h ! bb)sem i-leptonicnalstatewith relevantbackgroundsforan as-sum ed M h = 120 G eV andRLdt=30 fb  1 [8].which reducesthem ass-peak resolution (Figure5).Additionally,thereareseveralphysicsbackgroundstoconsider.ThettjjbackgroundrequiresATLAS tooptim isethe lightjet rejection fraction when b-tagging jets,whilstttbb appearsgenerallythrough Q CD gluon radiation (giving four b-jets in the nalstate). K inem aticinform ation can typically be used to dierentiate this background from signal,becausethe extra b-jetsarenotfrom a Higgsboson.Theanalysisselectseventswith a high jetm ultiplicity ( 6),and atleastfourb-tagged jets.The m issing transverseenergy isused to reconstructthe nalstateneutrino.Thetwo W -bosonsand top-quarksarerequired to be reconstructed (torem ovebackground),and nally therem aining b-jetsarecom bined to reconstructthe Higgs boson. The ATLAS analysis [8]has a signicance of 2:4 for M h =120 G eV,which falls as M h increases (due to the rapid decrease in H ! bbbranching ratio).3.6 T he M SSM H iggs discovery potentialofAT LA SIn theM SSM atBorn level,theHiggssectorphenom enology isdeterm ined by twoparam eters,the vacuum expectation value ratio ofthe two Higgsdoubletstan,and theHiggsm assM A .TheM h-m ax scenario (whereSUSY param etersgivethelargestvalue for M h) correspondsto the m ostconservative exclusion from LEP.The ATLAS discovery potentialforthisscenario isshown in Figure6.Iftan &M A do in fact lie in the m oderate tan and large M A region ofFigure 6,thenonly one Higgs boson willbe found. In this case,other observablessuch as theratio B R(h ! W W )=B R(h ! )willbe used to inferthe possible existence ofa supersym m etricHiggssector.5Figure 6: ATLAS discovery potentialfor light and heavy neutraland chargedHiggsbosonsforRLdt= 300 fb  1 in the M h-m ax scenario [9].4 C onclusionsThe ATLAS experim ent has discovery potentialfor a SM Higgs boson over them ass range dened by the LEP exclusion lim it ofM h > 114:4 G eV (95% C.L.)[10],to  1 TeV [11].A signicantregion ofM SSM param eterspace would yielddiscovery ofm ultiple supersym m etricHiggsparticles,should they exist.R eferences[1]The ATLAS Collaboration,CERN/LHCC/1999-14 & 15 (1999).[2]U.Agliettietal.,TeV4LHC W orkingG roup,Tevatron-for-LHC Report:Higgs,hep-ph/0612172,2006.[3]V.Bargeretal.,Phys.Rept.286 (1997)1.[4]S.Asaietal.,Eur.Phys.J.C 32 S2 (2004)19.[5]M .Bettinellietal.,ATL-PHYS-PUB-2007-013 (2007).[6]K .Cranm eretal.,ATL-PHYS-2003-025 (2003).[7]C.P.Buszello etal.,Eur.Phys.J.C 32 (2004)209.[8]J.Cam m in and M .Schum acher,ATL-PHYS-2003-024 (2003).[9]J.Haller,PoS HEP2005 (2006)338.[10]TheLEP W orkingG roup forHiggsBoson Searches,Phys.Lett.B 565 (2003)61.[11]N.Cabbibo etal.,Nucl.Phys.B 158 (1979)295.6

The Higgs discovery potential of ATLAS

Christopher Collins-tooth

CiteSeerX

THE HIGGS DISCOVERY POTENTIAL OF ATLAS

Higgs boson production and decay at the LHC will be described, together with related ATLAS search channels in order to provide an overview of the ATLAS Higgs discovery potential

Collins-Tooth, C

The Higgs Discovery Potential of ATLASChris Collins-ToothUniversity of Glasgowfor the ATLAS CollaborationOutline• LHC running conditions, event rates• SM Higgs production & decay at the LHC• The ATLAS detector  • Latest from Tevatron• ATLAS SM Higgs sensitivity, and a selection of channels• Basic MSSM scenarios – Only CP conserving considered here• Conclusions6-Sept-2007 C. Collins-Tooth  - HS07 2Running Conditions & Event Rates• First pp collisions expected from Summer 2008, √s=14 TeV.• Luminosity scenarios:– For 2008: (initial running)• L < 1033 cm-2 s-1 ∫Ldt 1 fb-1  ,  ~  – For 2009: (low-luminosity phase)• L = 1-2 1033 cm-2 s-1, ∫Ldt < 10 fb-1,• 30 fb-1 between 2008 and 2010/2011– Beyond: (high-luminosity phase)• L~1034 cm-2s-1, • ~300 fb-1 by 2014/2015• Pile-up:– ATLAS expects ~2 (low-lumi) or 20 (high-lumi) p-p minimum bias interactions per bunch crossing (25 ns)6-Sept-2007 C. Collins-Tooth  - HS07 3LHC SM Higgs Production and Decay• Production processes , K-factors and cross-section uncertainties:gluon fusion gg ⇒H  K~2.0, σ uncert ~10-20% NNLOVBF ’ ’ ’H K 1 2 t 5% NLO qq  ⇒ q q   ~ . , σ uncer  ~  Z,W assoc. qq⇒ HZ,W       K~1.4, σ uncert ~5% NNLOassoc. top gg,qq⇒ Htt K~1.1, σ uncert ~10% NLO          6-Sept-2007 C. Collins-Tooth  - HS07 4LHC SM Higgs Production and Decay• Production processes , K-factors and cross-section uncertainties:gluon fusion gg ⇒H  K~2.0, σ uncert ~10-20% NNLOVBF ’ ’ ’H K 1 2 t 5% NLO qq  ⇒ q q   ~ . , σ uncer  ~  Z,W assoc. qq⇒ HZ,W       K~1.4, σ uncert ~5% NNLOassoc. top gg,qq⇒ Htt K~1.1, σ uncert ~10% NLO          SM Higgs Branching Ratios (NLO, few % accuracy)6-Sept-2007 C. Collins-Tooth  - HS07 5ZZLHC SM Higgs Production and Decay• Production processes , K-factors and cross-section uncertainties:gluon fusion gg ⇒H  K~2.0, σ uncert ~10-20% NNLOVBF ’ ’ ’H K 1 2 t 5% NLO qq  ⇒ q q   ~ . , σ uncer  ~  Z,W assoc. qq⇒ HZ,W       K~1.4, σ uncert ~5% NNLOassoc. top gg,qq⇒ Htt K~1.1, σ uncert ~10% NLO          SM Higgs Branching Ratios (NLO, few % accuracy)LEP l d dexc u e6-Sept-2007 C. Collins-Tooth  - HS07 6LHC SM Higgs Production and Decay• Production processes , K-factors and cross-section uncertainties:gluon fusion gg ⇒H  K~2.0, σ uncert ~10-20% NNLOVBF ’ ’ ’H K 1 2 t 5% NLO qq  ⇒ q q   ~ . , σ uncer  ~  Z,W assoc. qq⇒ HZ,W       K~1.4, σ uncert ~5% NNLOassoc. top gg,qq⇒ Htt K~1.1, σ uncert ~10% NLO          SM Higgs Branching Ratios (NLO, few % accuracy)LEP l d dexc u ebbγγττ6-Sept-2007 C. Collins-Tooth  - HS07 7WWZZThe ATLAS DetectorInner Detector: pixels, silicon Primary features:•High hermeticity (e.g. for missing Et:ν...)•Excellent ECAL energy resolutionP f l i t ki strips, transition radiation trackersurrounded by SC solenoid B=2T (e.g. H→bb)• ower u  nner rac ng•Efficient muon ID and momentum meas.•Energy scale: e/γ~0.1%,µ~0.1%,Jets~1%EM Calorimeters: Pb/LArσ/E~10%/√E. e±,γ identification, angular resolution γ/jet & γ/π0 ti ( H H ZZ 4separa on e.g. →γγ, → → e)Hadronic Calorimeters: Fe scint. Cu-LAr). σ/E~50%/√E+0.03Muon Spectrometers: precision Jet, ETmiss measurements (e.g. H →ττ, H→bb)tracking drift chambers and trigger chambers <B>=0.6T, σ/pT ~ 7-10% at 1 TeV( )Air-Core Barrel Toroid6-Sept-2007 C. Collins-Tooth  - HS07 8e.g. H,A→µµ, H→4µ  Latest from Tevatronction )CL on Higgs uction cross-secalised to SM 95% produnorm(• CDF has roughly half it’s planned luminosity gathered already.• Together with D0, they may soon be able to exclude a Higgs around MH~160 GeV. • Consider also LEPEWWG: MH<182 GeV (including LEP2 MH>114.4 GeV) ? Suggests a low mass Higgs.6-Sept-2007 C. Collins-Tooth  - HS07 9MH [GeV]ATLAS SM Higgs Sensitivity• Caveats:Production cross-sections here are only LO–      .– Updated  analyses, alternative generators, full G4 simulation: coming December 2007.ATLAS should make a light Higgs discovery•        (MH<180 GeV) with ∫Ldt=30 fb-1.• Discovery in the region MH<120 is clearly the most challenging & will probably require several      channels to be combined. • ATLAS could make a discovery with much less        luminosity, given favourable MH. • By combining VBF,γγ,ttH→bb,ZZ*, discovery of a Higgs MH >120 GeV could be made at ∫Ldt=10 fb-1.        • 2MZ<MH<500 GeV: H →ZZ→4l gold-plated6-Sept-2007 C. Collins-Tooth  - HS07 10    channel « easy »H→ZZ*→4l±• Features: – Clean signature (but low stats: σxBR(H?4l) ~3-11fb for MH=130-200 GeV).– Benchmark channel for detector performance: ATLAS must have good EM  energy resolution, combined with good momentum resolution.– Mass peak can be produced, 4e, 4µ, 2e2µ differ by resolution; typically 1 5 2 G V~ .  -  e .• Backgrounds:– irreducible: ZZ*/γ∗→4l continuum ( ZZ*/ * k @ NLOqq→ γ  nown  . 20% added to account for gg →ZZ*/γ*)– reducible: tt→4l+X, Zbb→4l+X (non isolated leptons high impactreducible-  ,   parameter)– ZZ background is dominant after selection.Get background shapes & normalisation from–       data to minimise PDF/Luminosity uncertainties.6-Sept-2007 C. Collins-Tooth  - HS07 11H → γγ• Features:– Narrow mass peak over smooth background, region of interest MH<140 GeV.– Benchmark channel for detector performance: ATLAS EM Cal resolution and primary vertex determination. Powerful particle ID required to reject jets in backgrounds (rej. >103 for εγ=80%)• Backgrounds:– Irreducible γγ continuum :   • Born(qq→γγ), Box(gg→γγ) ,q Brehms. (qg →qγ →qγγ)  • γγ background computed at NLO (agrees with Tevatron).– Reducible:• jj or γj where jet is misidentified as γ        • Event selection: – Isolated photons (calorimeter and tracking cuts)– Higgs z-vertex reconstruction: σz=40μm (L=2.1033cm-2s-1); σz=1.6cm (L=1034cm-2s-1) – Fine calo segmentation for π0 rejection• Recovery of conversions~30 40% of photons convert in the inner detectorMγγ [GeV/c2]– -        .• Significance (30 fb-1):– new(NLO):6.3– Improvement expected from likelihood analysisATLAS: L.Carminati,Phys @ LHC066-Sept-2007 C. Collins-Tooth  - HS07 12    .Vector Boson Fusion Forward jet qForward jetFeatures: • 2nd most important production process (σ~10-20% of gg fusion)Forward jets• H decay products between two forward tag-jets.• No central jets (no q-q colour exchange). • Leptonic final state: leptons are spin correlatedφη        ? for lνlν final state, l+,l- in same direction.Higgs DecayZeppenfeld et al.• Look for:η=(η1+η2)/2|η1-η2|>4.4 – H→ττ, WW• Event selection:– ηj1. ηj2 < 0– |Δηjj| > 3.5 – 4– Mjj > 500–700 GeV• Pile-up may give fake central jets also harder to ,    identify tag-jets.• VBF may not be viable at high luminosity.6-Sept-2007 C. Collins-Tooth  - HS07 13VBF H→WWM i b k d WWjj tt• a n ac groun s: , • H→WW→lνjj – Sig 4.6 at MH=160 GeV for ∫Ldt=30 fb-1       • H→WW→lνlν – No mass peak as two missing momenta.T– ransverse mass– Sig > 5.0 for MH ≈125-190 GeV for ∫Ldt=30 fb-1Background uncertainty 7-10%MH=120GeVWW?eμMH=160GeVWW?eμ6-Sept-2007 C. Collins-Tooth  - HS07 14ttH H→bb• Features: – Attractive due to large BR(H→bb) at MH<130 GeV.bbhadronic W• Combinatoric background:– There are many ways to combine objects in the event bbleptonic W? Mass peak resolution quite low. • Physics backgrounds: – Backgrounds must be determined from d t (ttjj) d d t l h ia a, σ  epen en  on sca e c o ce. – Shape (highly dep on mistagging): use random tagging to estimate shape error.– Normalisation: from the sidebands   .– ttjj: b-tagging optimised to reject light jets.– ttbb (EW/QCD): 2 extra b-jets are not from a Higgs (typically QCD gluon radiation).    ?Kinematic info can then be used to reject bg.– S/√B = 2.86-Sept-2007 C. Collins-Tooth  - HS07 15ttH H→bb• Features: – Attractive due to large BR(H→bb) at MH<130 GeV.bbhadronic W• Combinatoric background:– There are many ways to combine objects in the event bbleptonic W? Mass peak resolution quite low. • Physics backgrounds: – Backgrounds must be determined from d t (ttjj) d d t l h ia a, σ  epen en  on sca e c o ce. – Shape (highly dep on mistagging): use random tagging to estimate shape error.– Normalisation: from the sidebandsSemi-leptonic: trigger on high Pt isolated e,μ   .– ttjj: b-tagging optimised to reject light jets.– ttbb (EW/QCD): 2 extra b-jets are not from a Higgs (typically QCD gluon radiation).    ?Kinematic info can then be used to reject bg.– S/√B = 2.86-Sept-2007 C. Collins-Tooth  - HS07 16ttH H→bb• Features: – Attractive due to large BR(H→bb) at MH<130 GeV.Select events with high jet multiplicity (≥6), at least 4 b-tagged jets.bbhadronic W• Combinatoric background:– There are many ways to combine objects in the event bbleptonic W? Mass peak resolution quite low. • Physics backgrounds: – Backgrounds must be determined from d t (ttjj) d d t l h ia a, σ  epen en  on sca e c o ce. – Shape (highly dep on mistagging): use random tagging to estimate shape error.– Normalisation: from the sidebandsSemi-leptonic: trigger on high Pt isolated e,μ   .– ttjj: b-tagging optimised to reject light jets.– ttbb (EW/QCD): 2 extra b-jets are not from a Higgs (typically QCD gluon radiation).    ?Kinematic info can then be used to reject bg.– S/√B = 2.86-Sept-2007 C. Collins-Tooth  - HS07 17ttH H→bb• Features: – Attractive due to large BR(H→bb) at MH<130 GeV.Select events with high jet multiplicity (≥6), at least 4 b-tagged jets.bbhadronic W• Combinatoric background:– There are many ways to combine objects in the event bbleptonic W? Mass peak resolution quite low. • Physics backgrounds: – Backgrounds must be determined from d t (ttjj) d d t l h ia a, σ  epen en  on sca e c o ce. – Shape (highly dep on mistagging): use random tagging to estimate shape error.– Normalisation: from the sidebandsSemi-leptonic: trigger on high Pt isolated e,μMi i Et d t   .– ttjj: b-tagging optimised to reject light jets.– ttbb (EW/QCD): 2 extra b-jets are not from a Higgs (typically QCD gluon radiation).ss ng  use  o reconstruct neutrino    ?Kinematic info can then be used to reject bg.– S/√B = 2.86-Sept-2007 C. Collins-Tooth  - HS07 18ttH H→bb• Features: – Attractive due to large BR(H→bb) at MH<130 GeV.Select events with high jet multiplicity (≥6), at least 4 b-tagged jets.Require W t’s tobbhadronic W• Combinatoric background:– There are many ways to combine objects in the event  ,   be reconstructed, bbleptonic W? Mass peak resolution quite low. • Physics backgrounds: – Backgrounds must be determined from d t (ttjj) d d t l h ia a, σ  epen en  on sca e c o ce. – Shape (highly dep on mistagging): use random tagging to estimate shape error.– Normalisation: from the sidebandsSemi-leptonic: trigger on high Pt isolated e,μMi i Et d t   .– ttjj: b-tagging optimised to reject light jets.– ttbb (EW/QCD): 2 extra b-jets are not from a Higgs (typically QCD gluon radiation).ss ng  use  o reconstruct neutrino    ?Kinematic info can then be used to reject bg.– S/√B = 2.86-Sept-2007 C. Collins-Tooth  - HS07 19ttH H→bbSelect events with high jet multiplicity (≥6), at least 4 b-tagged jets.Require W t’s to• Features: – Attractive due to large BR(H→bb) at MH<130 GeV.bbhadronic WUse remaining b- ,   be reconstructed, • Combinatoric background:– There are many ways to combine objects in the event bbleptonic Wjets for Higgs? Mass peak resolution quite low. • Physics backgrounds: – Backgrounds must be determined from d t (ttjj) d d t l h iMi i Et d tSemi-leptonic: trigger on high Pt isolated e,μa a, σ  epen en  on sca e c o ce. – Shape (highly dep on mistagging): use random tagging to estimate shape error.– Normalisation: from the sidebands ss ng  use  o reconstruct neutrino   .– ttjj: b-tagging optimised to reject light jets.– ttbb (EW/QCD): 2 extra b-jets are not from a Higgs (typically QCD gluon radiation).    ?Kinematic info can then be used to reject bg.– S/√B = 2.86-Sept-2007 C. Collins-Tooth  - HS07 20MSSM Higgs Discovery Potential• MSSM theory predicts 5 physical Higgs bosons: h0,H0,A0,H+,H- from two Higgs d bl tMhmax scenario: maximal Mh when Higgs-stop mixing largeNo mixing scenario: stop mixing set to 0Gluophobic scenario: coupling of h to gluons d d i d f ?h h?ou e s.• Higgs masses (to first order) are defined by two parameters:suppresse  es gne  or gg , γγ, h?ZZ?4lSmall α scenario: coupling of h to b(τ) suppressed designed for VBF, h?ττ and  tth,h?bb– tanβ ratio of ‘vev’ of 2 Higgs doublets– mA mass of cp-odd Higgs A0.• Four points chosen in parameter space6-Sept-2007 C. Collins-Tooth  - HS07 21MSSM Higgs Discovery Potential• MSSM theory predicts 5 physical Higgs bosons: h0,H0,A0,H+,H- from two Higgs d bl tMhmax scenario: maximal Mh when Higgs-stop mixing largeNo mixing scenario: stop mixing set to 0Gluophobic scenario: coupling of h to gluons d d i d f ?h h?ou e s.• Higgs masses (to first order) are defined by two parameters:suppresse  es gne  or gg , γγ, h?ZZ?4lSmall α scenario: coupling of h to b(τ) suppressed designed for VBF, h?ττ and  tth,h?bb– tanβ ratio of ‘vev’ of 2 Higgs doublets– mA mass of cp-odd Higgs A0.• Four points chosen in parameter space• If parameters are in fact in this region,     only single SM-like Higgs will be observed.• At least one Higgs should be found in all 4          CP conserving scenarios.• Promising channels: A/H H±– ⇒ μμ, ττ ;    ⇒ τν6-Sept-2007 C. Collins-Tooth  - HS07 22Conclusions• SM searches: ATLAS provides discovery potential over the entire mass range of a SM Higgs boson with 30fb-1 of           integrated luminosity.– Detector performance studies will be crucial.– Background shapes must be ascertained.• MSSM searches: The whole MSSM parameter i d b t l t Hi b fspace s covere  y a  eas  one ggs oson or 300fb-1 of integrated luminosity:Most difficult region: moderate tanβ large M–     ,  A.– If only one Higgs boson is observed, work is needed to distinguish between the SM and MSSM scenarios (e.g. looking at rates like:, which may deviate from SM predictions at low MA)6-Sept-2007 C. Collins-Tooth  - HS07 23    ……………….Finally…• ATLAS is approaching completion. 7 T V t b•  e  pro on eams expected in Summer 2008.6-Sept-2007 C. Collins-Tooth  - HS07 246-Sept-2007 C. Collins-Tooth  - HS07 25BACKUP MATERIAL6-Sept-2007 C. Collins-Tooth  - HS07 266-Sept-2007 C. Collins-Tooth  - HS07 27Inner Triplet review: Jun07• From FNAL: On Tuesday, March 27, a Fermilab-built quadrupole magnet, one of an “inner triplet” of three focusing magnets failed a high-pressure        ,    test at Point 5 in the tunnel of the LHC accelerator at CERN. • Weak points located in the anchoring to cold masses. To be reinforced on Q1 Q3 and DFBX,   .• Can be done in-situ6-Sept-2007 C. Collins-Tooth  - HS07 28ATLAS, CMS comparedSYSTEM ATLAS CMSINNER Silicon pixels+ strips Silicon pixels + strips TRACKER  TRT → particle ID (e/π)B=2Tσ/pT ~ 4x10-4 pT ⊕ 0.01   No particle identificationB=4T  s/pT ~ 1.5x10-4 pT ⊕ 0.005  EM CALO Pb-liquid argonσ/E ~ 10%/√E      Uniform longitudinal PbWO4 crystals σ/E~2.5%√Eno longitudinal segmentationsegmentation  HAD CALOFe-scint.  + Cu-liquid argonσ/E ~ 50%/√E ⊕ 0.03Cu-scint.  (> 5.8 l +catcher)σ/E ~ 100%/√E ⊕ 0.05MUON SYSTEMAir-core toroids σ/pT ~ 7 % at 1 TeVstandalone Fe → σ /pT ~ 5% at 1 TeVcombining with trackerMAGNETS Inner tracker in solenoid (2T)Calorimeters in field-free regionMuon system in air-core toroidsSolenoid  4T Calorimeters inside the field6-Sept-2007 C. Collins-Tooth  - HS07 29     (4T at peak, 0.5 T mean value)

The Higgs Discovery Potential of ATLAS

Higgs boson production and decay at the LHC is described, together with related ATLAS search channels, in order to provide an overview of the ATLAS Higgs discovery potential

The Higgs discovery potential of ATLAS

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