Higgs searches at LHC Higgs searches at LHC SM Higgs discovery - PowerPoint PPT Presentation

Higgs searches at LHC Higgs searches at LHC • SM Higgs discovery potential • SM Higgs parameters • MSSM Higgs discovery potential Giovanna Davatz, ETH Zurich On behalf of the ATLAS and CMS collaborations April 5th 2006, LISHEP conference, Rio de Janeiro 0 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

SM Higgs production processes at LHC M. Spira et al. NLO Gluon fusion Vector boson fusion LHC Most important for SM Higgs discovery: gluon fusion and vector boson fusion (VBF) VBF ≈ 10% of gluon fusion for m H < 200 GeV, comparable at m H 1TeV 1 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

Higgs decays: Branching ratios Djouadi, Kalinowski, Spira m H below 130 GeV: decay to bb dominates, But too large QCD background → no hope to trigger /extract fully hadronic final states → Look for final states with l (l=e, µ ), γ Large m H : decay almost entirely through WW and ZZ 2 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

Discovery Potential of SM Higgs at LHC Main discovery channels: 100 GeV < m H < 150 GeV: H → γγ , H → ZZ (*) → 4l, ttH → lbb+X, qqH → ττ 150 GeV < m H < 180 GeV: H → WW (*) → 2l2v Above 180 GeV: H → ZZ and H → WW channels LEP and el.mag. fits consistent with SM Higgs mass: 114.4 GeV < m H < 175 GeV @ 95% CL (new top mass Tevatron) 3 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

H → ZZ (*) → 4l • Clear resonance: very good mass resolution! • background can be fitted from sidebands • Experimental challenge: lepton mass resolution, rejection of non isolated leptons (tt, Zbb backgrounds) • golden channel! m H 130 GeV m H 170 GeV m H 150 GeV 4 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

H →γγ • Promising signature for Higgs boson mass region m H < 150 GeV • Rare decay channel: BR ~ 10 -3 • Large background S/B ≈ 1:20 – Reducible background (fake photons from jets and isolated π 0 ) – Irreducible background (prompt photons) • Requires excellent energy resolution and knowledge of primary vertex • Background can be estimated from side bands K-factors for signal and background included • Very good mass resolution of 1% expected 5 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

H → WW (*) → 2l2v • BR (H → WW) ≈ 1 for m H ~ 160 GeV (dip in the H → ZZ* sensitivity) • signature: 2 leptons plus high missing energy • Challenge: no narrow mass peak can be reconstructed → need good signal over background ratio, understanding of background • Large backgrounds WW, tt, Wtb significantly reduced by cuts on (i) Lepton angular correlation (ii) Jet veto: no jet activity in central detector region (Dittmar & Dreiner 1997) Signature leads to good signal/background ratio → New: For the first time full detector analysis and detailed studies of background uncertainties performed. Higher order corrections for signal and important background included 6 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

H → WW (*) → 2l2v p t lep max signal /background discovery potential CMS Very recently study with full systematics and detector simulation performed (CMS Note 2006/047): Result: signal over background ratio >1 for a large mass range, luminosity needed to detect Higgs in this channel (from 150 to 180 GeV): < 10 fb -1 For m H 165 GeV discovery with already 1fb -1 → discovery possible very soon after LHC starts! VERY PROMISING! 7 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

Higgs Search in Vector Boson Fusion Jet Motivation: Increase discovery potential Improve measurement of Higgs boson parameters (couplings to bosons, fermions) Je (proposed by D. Zeppenfeld et al. ) t Distinctive Signature of: Higgs Tag jets - two high p T forward tag jets φ - little jet activity in the central region ⇒ central jet veto η Forward jets are the “signature” of VBF Difference in pseudorapidity Pseudorapidity of jets Central jet veto effective for QCD background rejections, in QCD particular against the inclusive tt production (common Higgs background for all VBF channels) Higgs QCD Study should be repeated with full simulation and systematics 8 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

Higgs mass > 200 GeV Most important SM Higgs channels: ATLAS 200 GeV < m H < 700GeV: Inclusive H → ZZ, H → WW, leptonic decays m H > 700GeV: qqH → ZZ → 2l2v qqH → WW → 2l2j for high mass: decreasing sigma → good signatures from llqq and ll νν final states Large width Background: ZZ (/ WW) Z (W) + jets (neutrinos in jets or cracks in detector) (tt → WbWb) qqH → WW → 2l2j Better understanding of background when data available 9 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

Discovery Potential for SM Higgs CMS and ATLAS Full mass range can already be covered a few years after start of LHC Combined Atlas and CMS: full mass range with already 10fb -1 10 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

Determination of Higgs boson parameters 1.Mass Higgs boson mass can be measured with a precision of <1% over entire SM mass range → in H →γγ and H → ZZ → 4l resonances (ultimately 0.1%) 2. Coupling to bosons and fermions coupling measurements from various channels: gg → H, qq → qqH and others. Relative couplings can be measured with a precision of 10-20% (for 300 fb -1 ) 3. Higgs self-coupling Possible channel: gg → HH → WW WW → lv jj lv jj Small signal cross sections, large backgrounds from tt, WW, WZ, WWW, tttt, Wtt,... ⇒ so far, no significant measurement known at the LHC, sensitivity possible at SLHC 4. Spin Angular distributions in the decay channel H → ZZ(*) → 4l are sensitive to spin and CP eigenvalue. Needs large statistics 11 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

MSSM Higgs search Two Higgs doublets model: 5 physical states • 2 CP-even neutral Higgs bosons h 0 , H 0 • 1 CP-odd neutral Higgs boson A 0 H ± • 2 charged Higgs bosons 2 free parameters → common choice: • tan β - ratio of vacuum expectation values of the two doublets • m A - mass of pseudo-scalar Higgs boson At high M A the heavy bosons degenerate in mass MSSM neutral Higgs bosons (LEP) while the h does not go – M h , M A >92.9, 93.3 GeV @95% CL above a limit value of –M H ± >89.6 GeV @95% CL for BR(M H ± → τ v) =1 around 130 GeV –M H ± >78.6 GeV @95% CL for any BR 12 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

MSSM Higgses: H,A Production: mainly through gg → H/A, gg/qq → bbH/A Decay: 5 σ discovery reach Decoupling regime: High m A - decays to ττ : analyse leptonic and hadronic channels! - decays to µµ : lower BR, but better mass resolution Low tan β regime: tan β <5-10 - transition region between couplings to u- and d-type - use A → ZH, H → Wh, H/A → tt for very low tan β Intense coupling regime: Low m A , high tan β - Higgses are almost degenerated 13 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

MSSM Higgses: H ± Production: - for low mass: tt → tbH ± - for high mass: gg → t(b)H ± qq’ → H ± gg → H ± H ± gg → W ± H ± Decay: - for m H >~130GeV: H ± → t (*) b, dominates, but large background (tt+jets) - interesting for analyses: H ± → τν Reconstruction of the top decay and of the hadronic tau. tt and Wt backgrounds suppressed exploiting spin correlations 14 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

MSSM Higgses: h In decoupling limit (high M A ), the h behaves like a SM Higgs boson Decoupling regime High m A Decay: - h is SM-like (m h <135GeV!) Low tan β regime tan β <5-10 Decay: - h-couplings to WW/ZZ and u-type suppressed → bb, ττ , γγ decays Large parts of the plane covered VBF modes are important 15 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

MSSM Higgs boson discovery Assuming Susy particles are heavy m h < 135 GeV/c 2 m A ≈ m H ≈ m H ± at large m A 5 σ contours Main channels: h → γγ , tth → ttbb A/H → ττ , µµ H ± → τν , tb Plane fully covered (2x30 fb -1 ) 1 or more Higgs bosons Here only SM-like h can be observed observable if SUSY → chance to particles neglected. disentangle SM / MSSM 16 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006

Conclusion -Standard Model Higgs detectable with O(10 fb -1) over entire mass range -In some channels discovery possible already with less than 5 fb -1 ! -If discovered need to study Higgs parameters (mass, spin, CP, couplings, ..) -MSSM plane coverage requires few tens of fb -1 in a maximal mixing scenario -VBF important for the SM and MSSM Higgs discovery agradecimentos aos organizadores pelo evento muito legal! 17 Giovanna Davatz, ETH Zurich Higgs at LHC, LISHEP 2006