These proceedings summarize the sensitivity for the ATLAS and CMS experiments
at the LHC to discover a Standard Model Higgs boson with relatively low
integrated luminosity per experiment. A brief discussion on the expected
performance from these experiments in searches for one or more of the Higgs
bosons from the minimal version of the supersymmetric theories is also
included.Comment: Contribution to the proceedings of the XLIII Rencontres de Moriond
  (session devoted to QCD and High Energy Interactions), La Thuile, Italy. 4
  pages, 5 figure

Vickey, T.

English

arXiv

Vickey, T

CERN Document Server

Higgs Searches at the LHCTrevor Vickey•University of Wisconsin, Madison•On behalf of the ATLAS and CMS CollaborationsMarch 11, 2008XLIIIrd Rencontres de Moriond QCDTrevor Vickey / Moriond 2008 2The primary objective of the LHCElucidate the mechanism responsible for electroweak symmetry breakingAll experimental data to date favors a light Higgs• SM: MH =87+36-27 GeV;    MH < 160 GeV @ 95% CL• LEP Direct Limit: MH > 114.4 GeV @ 95% CLTHEORY EXPERIMENTT. Hambyeand K. Riesselmannhep-ph/9708416Λ is the scale of new physics beyond the Standard ModelSM Higgs Sector no longermeaningful for this ΛVacuum stabilityLEP Electroweak Working Group (Winter 2008)Trevor Vickey / Moriond 2008 3Higgs production at the LHCGluon-gluon FusionVector Boson FusionAssociated ProductionAllows fortriggering regardlessof Higgs decay modeThe two “spectator” quarks makefor a very distinct final stateNLO cross-sectionsM.Spira, Fortsch. Phys. 46 203-284 (1998)Large backgrounds for low-mass Higgs searches10-20% unc. NNLO<10% unc. NLO~10% unc. NLO<5% unc. NNLOTrevor Vickey / Moriond 2008 4SM Higgs discovery final statesAt low mass (MH < 2MZ)• Dominant decay through bb; enormous QCD background, suppressed in ttH• H→ττ accessible through Vector Boson Fusion (VBF)• H→WW(*) accessible through gluon-gluon fusion and VBF• H→γγ has a low BR (decays through top and W loops); but due to excellent γ/jet separation and γ resolution is still very significant• H →ZZ*→4l also accessible For higher masses• H→WW and H→ZZ→4l final-statesA. Djouadihep-ph/0503172Includes quark mass uncertainties (t, b, c) and αs(MZ)Trevor Vickey / Moriond 2008 5The ATLAS and CMS ExperimentsCMSATLASDesigned to search for the Higgs over a wide mass rangeHermetic calorimetry• Exceptional measurement of missing transverse energy, jets to high etaExceptional particle identification• Muons Efficiency ~90% Jet Rejection ~105• Electrons Efficiency ~80% Jet Rejection ~105• Photons Efficiency ~80% Jet Rejection ~103• b-Jet ID Efficiency ~60% Light Jet Rejection ~102• Tau ID Efficiency ~50% Jet Rejection ~102Electron, muon and photon energy and momentum resolution of ~2-3%15 m22 m46 m23 mTrevor Vickey / Moriond 2008 6Strategy and Start-up•Anticipating the start of the LHC• Summer 2008• Few ~100 pb-1 by the year’s end• Parts of both ATLAS and CMS have   already taken cosmic ray data•Understand the detectors…• Diagnose hot or dead channels• Tally up dead material• Tracking detector alignment• Tune the detector simulations to better match ATLAS and CMS•…do Standard Model measurements• Examine our standard candles• Demonstrate the ability to measure Ws, Zs and tops (b-jet identification)•…then search for the Higgs2008 ~100 pb-1 1031 – 1032 cm-2 s-12009 ~1 fb-1 1032 cm-2 s-12010 ~10 fb-1 2 x 1033 cm-2 s-12011 ~30 fb-1 2 x 1033 cm-2 s-12012 ~100 fb-1 2 x 1034 cm-2 s-1LHC The first five years?1 pb-1 = 3 days at 1031 cm-2 s-1Trevor Vickey / Moriond 2008 7H → ZZ(*)→ 4 lThe “Golden Mode”• Very clean signal (looking for final states with 4e, 4μ, 2e2μ)• Excellent mass resolution (1.5 – 2 GeV for MH = 130 GeV)• Powerful analysis in a wide mass rangeExperimental issues:• Zbb and tt rejection (leptons non-isolated, with activity around the leptons in the calorimeter and tracker; high impact parameter significance)• qq→ZZ known at NLO; gg→ZZ is added as 30% of LO qq→ZZ (no generator, yet)CMS 2e2μ at 5σ ATLAS CSC 2008 10 fb-1Trevor Vickey / Moriond 2008 8H → γγFinal state produced through W, top and bottom loopsPowerful for low masses• Significance of 6 – 8σ with 30 fb-1• Excellent mass resolution (~1.5 – 2 GeV)Experimental issues• Electromagnetic calorimeter calibration• Requires excellent γ/jet separation• Conversion recoveryRecent developments• Split events into categories (by jet multiplicity, energy ratios and η region)• Inclusive, 1 and 2-jet analyses; combine to increase significance• Use of fits and a Likelihood Ratio for discovery, systematicsATLAS CSC 2008 30 fb-1 H + 2 JetsTrevor Vickey / Moriond 2008 9H → γγDiphoton background now calculated at NLO• Agrees with the data from the TevatronBackgrounds can be taken from the sidebands…Signal with background Signal after background subtractionCMS 100 fb-1Inclusive AnalysisTrevor Vickey / Moriond 2008 10H →WW → 2l2υUnlike other channels, full mass reconstruction is not possible• Essentially a counting experiment• Accurate background estimate is criticalMost significant ~160 GeV• BR(H→WW) > 95%Dominant backgrounds• ttbar (suppressed with a jet veto)• WW (exploit spin correlations) CMSΔφll(Normalized to 1)Spin correlationsTrevor Vickey / Moriond 2008 11Forward Jet Tagging and the Central Jet VetoWe can get the upper-hand in the VBF channels Forward Jet Tagging• D. Rainwater, D. Zeppenfeld, et al.Central Jet Veto• V.Barger, K.Cheung and T.Han in PRD 42 3052 (1990)ηφHiggs decay productsTagging JetVeto events with extra jets in the central regionTagging JetTagging JetsS. Asai et al., ATL-PHYS-2003-005Trevor Vickey / Moriond 2008 12VBF H → ττA very significant channel for low masses• Important for studying the coupling of Higgs to leptons• Three final states lepton-lepton, lepton-hadron, hadron-hadron• Triggers for the fully hadronic mode are under investigationMass reconstruction via the collinear approximation• Approximation breaks down when the two taus are back-to-back• Mass resolution limited by missing transverse energy (~8 – 10 GeV)Experimental issues:• Tau tagging (Likelihood, Neural Net methods)• Z+jets background (especially for low masses)• tt rejection (b-jet ID and veto for lepton-lepton)CMS H→ττ→lνντjetν 30 fb-1Trevor Vickey / Moriond 2008 13VBF H → ττData-driven control samples are being explored for many backgrounds• The relative contributions from different jet multiplicities are not known• Unknowns related to critical analysis cut-specific variables existFor the dominant background, collect Z→μμ and Z→ee events from data and use TAUOLA to decay the leptons to tausS. Asaiet al., ATL-PHYS-2003-005In this way we can emulate each of the lepton-lepton, lepton-hadron and hadron-hadron final statesATLAS H→ττ→eννμνν 30 fb-1Obtain both the background shapeand normalization from dataTrevor Vickey / Moriond 2008 14VBF H →WW → lυqqOne of the best channels for intermediate and high Higgs masses• A VBF analysis reaping the benefits of the CJV and Tagging Jets selectionEvent Selection• VBF tagging jets selection• Central Jet Veto• Isolated lepton• 4 jets• Large missing transverse energyMass reconstruction possible• Backgrounds: ttbar, W+jets, WW+jets• Exploring data-driven approaches for obtaining background shapesCMSTrevor Vickey / Moriond 2008 15SM Higgs Discovery PotentialSignal significance of 5σLuminosity for discovery or exclusion• ~few 100 pb-1, some exclusion @ 95% CL• ~1 fb-1, 5σ discovery if MH ~160 - 170 GeV• ~10 fb-1, discovery over a broad mass rangeCMSATLAS 30 fb-1CMS 30 fb-1Trevor Vickey / Moriond 2008 16MSSM Higgs at the LHCMinimal Supersymmetric extension to the SM: (A, H, h, H±)• As one example here, consider A / H / h →μμ• Not visible in the SM• Enhanced in the MSSM by ~tan2β; excellent mass resolution as opposed to ττDirect and associated productionDivide analysis into two uncorrelated channelsInitial event selection:• Di-muon selection, low event MET, b-tag0 b-jet≥1 b-jet• Acoplanarity, sum pT of all jetsATLAS PreliminarytanβEnhanced for large tanβTrevor Vickey / Moriond 2008 17MSSM Higgs at the LHCCombine the 0 and ≥ 1 b-jet analyses to increase the significance• A very similar analysis has been explored for the ττ channelATLAS CSC 2008 10 fb-110 fb-1 Alone10 fb-1 Combinedtanβ for a 5σDiscoveryReconstructedInvariant massTrevor Vickey / Moriond 2008 18ConclusionsIf it is there, ATLAS and CMS are in a good position to find the Higgs…• Unless it is discovered first at the Tevatron• For a SM Higgs ATLAS and CMS need ~1 – 30 fb-1• How long will it take to get that much integrated luminosity from the LHC?• How quickly will we understand the detectors?Post-discovery questions that would need be answered…• Is it the simple Standard Model Higgs?• Does it have the expected couplings to various particle types?• Are there more Higgs particles (à la Supersymmetry)• Higgs discovery also raises the “hierarchy” problemATLAS and CMS are on track to try and answer these questions.Trevor Vickey / Moriond 2008 19Backup SlidesTrevor Vickey / Moriond 2008 20The ATLAS ExperimentTrevor Vickey / Moriond 2008 21The CMS ExperimentTrevor Vickey / Moriond 2008 22ttH(H→bb)A very complex final state• Good discovery channel at low masses• Determination of the Yukawa coupling• Dominant backgrounds tt+jets production• Also considering fully-hadronic and dilepton final states• Experimental issues:• b-tagging (efficiency ~εb4)• Good understanding of background shape at turn-overJ. Cammin and M. Schumacher, ATL-PHYS-2003-024bbbbjjlvTrevor Vickey / Moriond 2008 23MSSM Higgs at the LHCSummary of CMS reach in MA tan βTrevor Vickey / Moriond 2008 24MSSM Higgs with ATLASTrevor Vickey / Moriond 2008 25The ATLAS ExperimentTrigger and Data Acquisition System:• Level-1 is hardware, Level-2 confined to “Regions of Interest”, Event Filter has the ability to access the entire event~100 MB/s~1 PB/year (petabyte = 1015 bytes!)High-Level TriggerAverage Event Size ~2 MB< 10 μsTrevor Vickey / Moriond 2008 26ATLAS Data-taking ChainFirst test of end-to-end data-taking chain took place in September 2007Flow of data from CERN Tier 0 to Tier 1 sites all over the world.For data processing and analysis,the GRID is an absolute necessityAthena.pyRAWROOTPostScriptDPDAODTAGESDEventSelectionAOD andTAG builderRAW Event data from TDAQ:~2 MBESD (Event Summary Data): output of reconstruction (calo cells, track hits, ..): ~1 MBAOD (Analysis Object Data): physics objects for analysis (e,γ,m,jets, …): ~100 kBTAG (Event Level Metadata):Reduced set of information for event selection: ~1 kBDPD (Derived Physics Data): equivalent of old ntuples: ~10 kBTrevor Vickey / Moriond 2008 27The Large Hadron ColliderHoused in the former LEP tunnel• Dipole field at 7 TeV is 8.33 T• ~350 MJ per beam!• Ultimately ~2800 bunches • Vacuum 10-13 atm (~6500 m3 pumped)• 1232 Dipoles (operate at 1.9 K)• 858 Quadrupoles• Typical store lasts ~10 hours• Can also be used for ion running (Pb)• Final price tag estimated at 4G EURTrevor Vickey / Moriond 2008 28Expected LHC Event RatesProcess Events / s Events in 10 fb-1W→ev 15 108Z→ee 1.5 107ttbar 1 109bbbar 106 1012-1013H (m=130) 0.02 105ATLAS with LHC at L = 1033 cm−2 s−1Trevor Vickey / Moriond 2008 29VBF H → ττS. Asai et al., ATL-PHYS-2003-005Note: All cross-sections are shown in fbTrevor Vickey / Moriond 2008 30CMSSMConstrained MSSM• O. Buchmueller et al., arXiv:0707.3447v2 [hep-ph] • CMSSM: Mh = 110 (+8)(-10) ± 3 (theo.) GeV• Includes CDM, flavor physics and aμ experimental datachi2 / ndf = 17.34 / 14Trevor Vickey / Moriond 2008 31Central Jet Veto and Pile-upTrevor Vickey / Moriond 2008 32Impact ParameterTrevor Vickey / Moriond 2008 33Higgs Properties: MassTrevor Vickey / Moriond 2008 34Higgs Properties: WidthTrevor Vickey / Moriond 2008 35Higgs Properties: Cross-sectionsTrevor Vickey / Moriond 2008 36Higgs Properties: Couplings and BRsTrevor Vickey / Moriond 2008 37Higgs Properties: Branching RatiosTrevor Vickey / Moriond 2008 38Higgs Properties: CPAzimutal angle φ between decay planes in the rest frame of HiggsF(φ) = 1 + α cos(φ) + β cos(2φ)Polar angle θ between lepton and the Z momentum in Z rest frameG(θ) = L sin2(θ) + T(1+cos2(θ)), R=(L-T)/(L+T)MZ* distribution for MH < 2 MZ , dΓH/dMZ*2 ~ βn near threshold (n=1 in SM)β2=[1-(MZ+MZ*)2/MH2][1-(MZ-MZ*)2/MH2]Resent ATLAS fast simulation study on sensitivity to F(φ) and G(θ)for exclusion of 0-, 1+, 1- for MH > 2MZ:  SN-ATLAS-2003-025

Higgs Searches at the LHC

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