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A/H -> tt and H + -> tn in CMS

Physics at LHC Prague July 6 - 12, 2003. A/H -> tt and H + -> tn in CMS. R. Kinnunen. Helsinki Institute of Physics Helsinki, Finland. Contents. H/A -> tt. Cross sections and branching fractions Hadronic t trigger t -jet identification and hadronic jet suppression

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A/H -> tt and H + -> tn in CMS

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  1. Physics at LHC Prague July 6 - 12, 2003 A/H -> tt and H+ -> tn in CMS R. Kinnunen Helsinki Institute of Physics Helsinki, Finland R. Kinnunen Helsinki Institute of Physics

  2. Contents H/A -> tt Cross sections and branching fractions Hadronic t trigger t-jet identification and hadronic jet suppression t tagging with impact parameter measurement b-jet tagging in bbH/A Signal to background ratios and expected discovery reaches, tanb mesurement from event rates H+ -> tn Cross sections and branching fractions Trigger for H+ -> tn in fully hadronic events t polarization in H+ -> tn and W+ -> tn Signal to background ratios and expected discovery reaches, tanb mesurement from event rates R. Kinnunen Helsinki Institute of Physics

  3. How to search for heavy neutral MSSM Higgs bosons Relative to SM, H/A -> ZZ, WW are strongly suppressed but Hbb, Htt, Hmm couplings are enhanced at high tanb use bbH for production with H/A -> tt, mm decay channels - Efficient background reduction with b tagging in bbH/A - 3 final states for H/A -> tt (jet+jet, lepton+jet, lepton+lepton) - Higgs boson mass reconstruction for H,A -> tt, mm - H/A -> bb may be also viable (under study) R. Kinnunen Helsinki Institute of Physics

  4. Production and decay of H, A Production through gg -> H/A and gg -> bbH/A g H g gg->bbH/A dominates the production at large tanb: ~90% of the total production cros section b g H g b HIGLU,HQQ from of M. Spira et al. BR(H -> tt) ~ 10% for tanb > 10 Pole mass for Yukawa coupling H -> tt For large mA, enhancement of BR(H->tt) for larger |m| parameter due suppression of H,A -> cc decays R. Kinnunen Helsinki Institute of Physics

  5. Final states investigated for H, A ->tt H -> tt -> 2 t jets BR ~ 42.0% Backgrounds from QCD multijet events, Z,g* ->tt, tt, Wt, W+jets H, A -> tt -> lepton + t jet BR ~ 45.6% H, A -> tt ->2 leptons BR ~ 12.4% Backgrounds from Z,g* ->tt, tt, bb, Wt, WW, W+jets Simulation tools PYTHIA for event generation HDECAY for normalization of cross sections and branching fractions for two-t jet and two-lepton channels Full simulation for trigger, t selection, b tagging, mass reconstruction Fast simulation for signal to background ratios R. Kinnunen Helsinki Institute of Physics

  6. Hadronic Tau trigger Trigger requirements: Level-1 output rate of 1-Tau and 2-Tau triggers: 3 kHz at low luminosity 6 kHz at high luminosity HLT output rate on tape for t’s: 4 (10) Hz at low (high) luminosity Level-1 1-Tau and 2-Tau triggers The required Level-1 rate can be achieved with the thresholds of 93 (112) GeV for 1-Tau for low (high) luminosity 66 (76) GeV for 2-Tau for low (high) luminosity on the calorimeter jet reconstructed in 12x12 trigger towers with maximum Et in the central 4x4 towers and no significant activity in the neighbouring towers (trigger tower = HCAL cell + 5x5 ECAL cells, DhxDf = 0.087x0.087 in the barrel) Efficiency: 78 (54)% for H->tt, mH = 200 GeV, 1 or 2 Tau 81 (72)% for H+->tn, mH+ = 200 GeV, 1 Tau R. Kinnunen Helsinki Institute of Physics

  7. Level-2 Tau trigger Reconstruction of a jet centered at the hardest Level-1 t jet Isolation in the EM calorimeter: - sum of the Et deposits in ECAL within 0.13 < DR(jet direction, cell) < 0.4 Efficiency (QCD vs H->tt-> 1/3 prong jets) as a function of Etcut-off t jet definition: SEtem < Etcut-off Suppression of 3 for QCD background with SEtem < 5.6 GeV Signal efficiency ~ 85% same for mH = 200 and 500 GeV R. Kinnunen Helsinki Institute of Physics

  8. Level-3 Pixel Tau trigger using track counting in the Pixel (vertexing) detector: - good efficiency required, high pt accuracy not needed 1. Reconstruction of tracks around the Level-1 jet direction 2. Small signal cone (DRS = 0.07) around the hardest track 3. Larger isolation cone around jet direction Efficiency (QCD vs H->tt-> 1/3 prong jets) as a function of the isolation cone size Accept tracks only in the signal cone HLT efficiency for 1 or 3 tracks in the signal cone and for DR = 0.35: QCD suppression ~ 103 signal efficiency ~ 40% R. Kinnunen Helsinki Institute of Physics

  9. Off-line t jet identification Exploits further the narrowness and the isolation of the t jet in the full tracker 1. Leading track cut: Find the leading track in the L1 t jet, set a cut pt > 40 GeV Define a narrow signal cone Dr = 0.03 (0.07 for HLT) around the leading track direction 2. t jet isolation: No track, pt > 1 GeV, allowed within 0.03 < DR < 0.4 3. Number of tracks in the signal cone: 1 or 3 tracks in the signal cone (ptleading > 40 GeV) 4. Further reduction of hard QCD jets: Very hard QCD jets can be further suppressed with a cut in ptleading / Etjet R. Kinnunen Helsinki Institute of Physics

  10. Simulation of the QCD di-jet background using (for the moment) a rejection factor as a function of Etjet (initial QCD di-jet rate ~1012 events for 60 fb-1) t selection efficiency for hadronic QCD jets from fast simulation Suppression of ~ 1000 per jet can be obtained Signal efficiency (per event) including Level-1 and HLT trigger from full simulation: mH = 200 GeV 0.8% mH = 500 GeV 8.9% efficiency verified with full simulation and complet reconstruction for ptgen < 170 GeV R. Kinnunen Helsinki Institute of Physics

  11. t impact parameter tagging in H -> tt The t lifetime is small, ct ~ 90 mm, but can be still used to further supress the fake t’sfrom Z -> lland from QCD multi-jet events using impact parameter measurement (1 or 3 prong t’s) and vertex reconstruction (3 prong t’s) Best separation combining the measurements in the two t jets into one variable CMS full simulation and reconstruction sqrt(sip(t1)2 + sip(t2)2) where sip(t1) and sip(t2) are significansies of the impact parameter measurements of the leading tracks in jets 1 and 2 S. Lehti Signal efficisiency ~ 60% QCD suppression factor of ~ 9 R. Kinnunen Helsinki Institute of Physics

  12. B jet tagging in gg -> bbH/A Tagging of the associated b jets is the most efficient way to reduce the Z,g* -> tt (bbZ ~ 1-2 %)and to further reduce the QCD multijet events Associated b jets in gg -> bbH/A are soft and uniformly distributed over |h| < 2.5: Efficiencies (Et threshold + tagging propability) relatively low Significance of the signed transverse impact parameter CMS full simulation and complete reconstruction Tagging algorithm: at least 2 tracks, pt > 1 GeV, sip > 2, inside the jet cone non-t jets in gg -> bbH/A Efficiency per jet: 32% non-t jets in bbH ~ 2 % light quark and gluon jets jets in QCD di-jet events R. Kinnunen Helsinki Institute of Physics

  13. Higgs boson mass reconstruction in H -> tt The neutrinos from H -> tt (t -> hadrons+n, t -> l+nn) are emitted close to the directions of the visible t’s (jets or leptons): Etmiss neutrino reconstruction possible using the Etmiss measurement in events with Df(t1,t2) < 180o, efficiency ~ 50 % (for En1 En2 >0) t jet, e, m t jet, e, m qjj mH = sqrt(2 En1 En2 (1-cosqjj)) jet Higgs boson mass from full simulation for H -> tt -> two jets, mH = 500 GeV, tanb = 20, with Df(t jet1,t jet2) < 175o Efficiency (Df cut, En1 En2>0)36% sfit 14.9% Efficiency and resolution sensitive to the Etmiss measurement and to the Df(t1,t2) cut R. Kinnunen Helsinki Institute of Physics

  14. Event selection for A,H->tt -> 2 t jets • Basic event selection: • - 2 t jets passing the Level-1 and HLT triggers • and the off-line t selection (1 or 3 hard tracks, isolation) • - t tagging with impact parameters • Higgs boson mass reconstruction (Df(t1,t2) cut, En1, En2 > 0) Two alternatives for further reduction: i) Further selection with Etmiss: - Etmiss > 40 GeV -central jet veto beyond 30 GeV ii) Further selection with b-jet tagging: - one b-tagged jet, Et > 20 GeV - central jet veto beyond 30 GeV Total background Total background Total background larger staistics but poor S/B much improved S/B but lower statistics R. Kinnunen Helsinki Institute of Physics

  15. Leptonic final states, H/A -> tt -> em, ll Event selection: - 2 isolated leptons, pt > 20 GeV - one tagged b jet, veto on second central jet beyond 30 GeV - impact parameter t tagging lepton+lepton final states can be used to double the statistics - Higgs boson mass reconstruction H/A -> tt -> em mA = 200 GeV tanb = 20 H/A -> tt -> ll lepton + t jet final states, H/A -> tt ->l + t jet Event selection: - one isolated lepton (pt > 20 GeV), one t jet (Et > 40 GeV) - one tagged b jet, second jet veto - Higgs boson mass reconstruction Reach not yet optimized for large mA (> 200 GeV) in CMS R. Kinnunen Helsinki Institute of Physics

  16. Expected 5s-discovery reach for H/A -> tt Results for H/A -> mm from full simulation and complete reconstruction Higgs boson mass resolution ~ 2% Variation of BR(H -> tt) due to H -> cicj decay modes ~ 40% at mH=500 GeV, tanb=20, for -200 GeV < m < 500 GeV R. Kinnunen Helsinki Institute of Physics

  17. Measurement of tanb in H -> tt from event rates using the tanb dependence s*BR ~ tan2b * x Dtanb/tanb = ½ * sqrt((NS+NB) / NS2 + (DL/L)2 + (Dx/x)2) - Luminosity uncertainty DL/L ~ 5% - Theoretical uncertainty on the cross section for gg -> bbH: dx/x ~ 30% - The gg -> bbH component is selected by b jet tagging: 1b or 2b tagging, less theoretical uncertainty and higher experimental purity with 2b tagging Dtanb/tanb 1b tagging 2b tagging H/A -> tt -> 2 t jets, mA= 500 GeV, tanb = 40, 60 fb-116% 19% dominated by rate uncertainty up to tanb ~ 30 H/A -> tt -> lepton + t jets, mA= 200 GeV, tanb = 20, 30 fb-116% H/A -> tt -> em, mA= 140 GeV, tanb = 14, 30 fb-1 18% Precision of Higgs boson mass measurement in H/A -> tt -> 2 t jets mA= 500 GeV, tanb = 40 , 60 fb-1DmH/mH = 1.5% mA= 200 GeV, tanb = 40 , 60 fb-1DmH/mH = 1. 2% R. Kinnunen Helsinki Institute of Physics

  18. How to search for charged Higgs bosons at LHC If mH+ < mtop: Production through tt events, t -> bH+ - accessible through the H+ -> tn, t2-> lepton+qqfinal state If mH+ > mtop: Production through gg -> tbH+, gb -> tH+, qq’ -> H+, gg -> H+H-, gg -> W+H- - gg -> H+H-, gg -> W+H- have small production cross sections • Event rate sufficient for qq’ -> H+-> tn but suppression of • the qq’ -> W-> tn background is difficult t g H+ g b • gg -> tbH+, gb -> tH+ most promising processes, • cross sections large enough andtheassociated top • and b jets can be used for background reduction g t H+ b R. Kinnunen Helsinki Institute of Physics

  19. One tagged b jet enough to suppress the backgrounds, use gb -> tH+ Event generation with PYTHIA Normalization of the production cross sections to T. Plehn, MADPH-02-1275 Normalization of branching fractions to HDECAY H+ -> tn T. Plehn HDECAY tanb = 30 R. Kinnunen Helsinki Institute of Physics

  20. Trigger for H+ -> tn, t -> jet + n Level-1: single Tau trigger (Et > 93 GeV, low luminosity) High Level Trigger: cut on Etmiss in the calorimetry (possible due to off-line Etmiss > 100 GeV) QCD rejection ~ 100 for Etmiss > 65 GeV Level-3 Single Tau: Efficiency (QCD vs H->tt-> 1/3 prong jets) as a function of pt cut for the leading track • Cut on the leading track • and isolation needed - Reconstruction of tracks in the full tracker within the L1 t jet Efficiency for ptleadingtrack > 20 GeV and isolation in 0.065 < DR < 0.4: QCD rejection ~ 30 Signal efficiency ~ 58% R. Kinnunen Helsinki Institute of Physics

  21. t polarization in H+ -> tn and W+ -> tn n t+ n t+ W+ H+ n p+ p+ t+ n t+ H+ -> t+n leads to harder pions from t -> p+n and from the longidutinal components of r and a1 than the corresponding decays in W+ -> t+n TAUOLA interfaced to PYTHIA Large suppression of W -> tn in tt, Wt, W+jet using the cut: pleadingtrack / Etjet > 0.8: tt background t jet = calorimeter jet from t -> hadrons + n t -> p+n rT ,a1T rL Signal, mH+= 400 GeV 46% Signal, mH+= 200 GeV 22% tt background 1.8% rL ,a1L Signal R. Kinnunen Helsinki Institute of Physics

  22. Event selection for gb -> tH±, H± ->tn - Ettjet > 80 – 100 GeV, containing a hard track with pttrack/Ettjet > 0.8 - Etmiss > 100 GeV mT(t jet, Etmiss) - Reconstruction of associated hadronic top from two jetand one b-tagged jet - Veto on 5th jet, veto on second top quark 30 fb-1 background Quasi two-body decay between the t jet and Etmiss in fully hadronic events -> almost background-free situation in mT(t-jet,Etmiss) Signal Df(t jet, Etmiss) > 20o Df(t jet, Etmiss) Cut on Df(t jet, Etmiss) -> low mass background can be suppressed 30 fb-1 background tt background Signal Signal R. Kinnunen Helsinki Institute of Physics

  23. Expected 5s-discovery reach for charged Higgs boson H+ -> tb and qq’ -> H+ -> tn are also promising Excess of t’s can be measured in tt, t -> bH+, H+ -> tn for mH+ < mtop good background knowledge needed No sensitivity for intermediate tanb with gb -> tH+ (with SM decay channels): H+ -> Wh, h -> bb accessible (in MSSM) only at small tanb tanb measurement from event rates using s ~ tan2b at high tanb Expected uncertainty for tanb >30 with 20% theoretical uncertainty : Dtanb/tanb < 14% for mH+ = 200 GeV Dtanb/tanb < 20% for mH+ = 400 GeV R. Kinnunen Helsinki Institute of Physics

  24. Conclusions Search for H/A and H+ can start early, with < 10 fb-1 With ~ 60 fb-1 masses in the 500 – 800 GeV range accessible more specifically: H/A ->tt accessible for 30 fb-1 with em and ll final states for tanb > 14 at mA = 140 GeV jet+ lepton final states for tanb > 10 at mA = 200 GeV and for 60 fb-1 with 2 t jet final states for tanb > 18 at mA = 200 GeV tanb > 25 at mA = 500 GeV H+ -> tn accessible in gb -> tH+ in fully hadronic final states with 30 fb-1 for tanb > 20 at mA = 200 GeV tanb > 32 at mA = 400 GeV DmH/mHin H/A -> tt -> 2 t jets, tanb = 40, 60 fb-1 : 1.2% for mA = 200 GeV 1.5% for mA = 500 GeV • tanb determination with event rates: • Dtanb/tanb = 16% for H/A ->tt -> 2 jets, mA = 500 GeV, tanb = 40 • 16% for H/A ->tt -> lepton+jet, mA = 200 GeV, tanb = 20 • 18% for H/A ->tt -> em, mA = 140 GeV, tanb = 14 • 14% for gb -> tH+ ,H+ -> tn , mA = 200 GeV, tanb = 30 R. Kinnunen Helsinki Institute of Physics

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