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Physics of Charged Higgs Boson(s) at the LHC

This seminar outlines the physics of Charged Higgs Bosons at the Large Hadron Collider (LHC), covering topics like MSSM, charged Higgs production, decays, and their properties. The discussion includes detailed analyses of Higgs fields, discovery modes, production cross-sections, decay channels, and recent research progress in signal generation methods. Special attention is given to charged Higgs search in ttbar production, different decay scenarios, and event selection strategies. Theoretical frameworks, experimental implications, and potential significance in particle physics research are explored.

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Physics of Charged Higgs Boson(s) at the LHC

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  1. Physics of Charged Higgs Boson(s) at the LHC Outline: • Introduction • MSSM • Charged Higgs Production and Decays • M(H±) < 170 GeV • ttbar  bWbH±  blνbτν (TDR) • ttbar  bWbH±  bqqbτν(new) • ttbar  bWbH±  blνcs • M(H±) > 180 GeV • gb  tH±, H± tb,t  blν(TDR) • gb  tH±, H±  τν, tbqq (new) • gg  tbH±  tbtb • Properties – mass and tanβ determination • Summary Marian Zdražil Friday Physics Seminar January 28, 2005

  2. Introduction

  3. MSSM Higgs(es) • Complex analyses; 5 Higgses: F =h0, H0, A0, H; • At tree level, all masses and couplings depend on only two parameters; traditionally taken to be MAand tanb (Born level, mh<MZ) • 2 complex Higgs doublets  8 d.o.f. 3 eaten by massive vector bosons W±/Z  5 physical Higgs fields • For tanβ > 1. A, H, H± couples dominantly to the heaviest lepton (τ) and to the heaviest down type quark (b) • Radiative corrections from loop containing top quarks & SUSY particles are substantial  searches are affected MH±2 = MA2 +MW2

  4. MSSM Higgs Discovery modes • Large variety of observation modes • if SUSY particles heavy • SM-like:h gg, bb; H  4l • MSSM-specific:A/H mm, tt, tt ; H  hh, A  Zh; H tn • if SUSY particles accessible: • H/A  c20c20 4l + missing Energy • h produced in cascade decays (e.g. c20 hc10) • H± decays into lightest chargino c1± and neutralino c10 or decays to sleptons would dominate when kinematically allowed • Studies performed in two steps: • SUSY particles are heavy: no contribution to Higgs production/decay  decays only into SM particles possible • SUSY particles contribute in production/decays

  5. Charged Higgs Production and Decays (i) • Charged Higgs bosons have masses that are almost degenerate with the masses of H- and A-bosons. Only a few production mechanisms are possible (assuming a heavy SUSY spectrum): MH < 170 GeV/c2 ppbar  ttbar production (gg fusion process ~90%) σ(tt incl.) ~ 833 pb  over 8M events in ∫L dt = 10 fb-1 ~ 320 pb (leptons) • t H± b decays: • Charged Higgs searches might be performed in this channel up to kinematic limit imposed by top quark mass • BR is large at SMALL and LARGE tanβ (for a given MH) but it has a pronounced minimum at tanβ ~ √mtop / mb ~ 7.5 BR(tH±b) ~ mt2 cotan2β + mb2 tan2β the depth and an exact position is sensitive to QCD corrections to the running b-quark mass • H± decay channels: H±  τν (BR~100%) H±  h°W*, H±  AW* • H±  cs and H±  bt*  bbW • (low tanβ non-negligible) (150 GeV < H± < 180 GeV) 3-body off-shell decays: STUDIED:

  6. Charged Higgs Production and Decays (ii) If MSSM Charged Higgs exists, the ttbar production cross-section will be reduced to ~240 pb, ~130 pb for Higgs masses 110 GeV, 130 GeV respectively (tanβ~1.5). That could be a hint that there is a Charged Higgs boson ! Signal rates are only 1.7 pb, 0.7 pb respectively.

  7. Charged Higgs Production and Decays (iii) MH > 180 GeV/c2  above tb threshold Produced by gluon-gluon and gluon-b fusion or by other b-quark initiated processes: FINAL STATE: gg  H± tb : 2 top quarks and 2 b-quarks gb  H± t : 2 top quarks and a b-quark ( possibility to reconstruct top-quark pairs ) COMMON CHARACTERISTICS:multi b-jet final states with at least one top-quark tanβ MH [GeV] 30. 1.5 10. DECAY CHANNELS: tanβ > 10 (high) : H±  tb and H±  τν BR(tb)~80%, BR(τν)~20% tanβ < 1.5 (low) : H±  tb only ! BR~100% Production cross-section [pb] for bg  H±t

  8. Charged Higgs Production and Decays (iv) Recent progress on understanding how to generate signal… (2 2) = gb tH+ (2 3) = gg tbH+

  9. M(H±) < 170 GeV(below mtop-mb)

  10. tt  bWbH±  blνbτν • “Leptonic channel” (D. Cavalli et al., ATL-PHYS-94-53): • tH+b; H+; hadrons ; IDEA:Enhanced tau-lepton rate in ttbar decays • mass of H± cannot be directly reconstructed because several neutrinos are produced in the final state • Excellent τ-ID is a must ! • Measurement of significance of the event excess with an isolated τ with respect to rate foreseen by SM universality SIGNAL: BACKGROUNDS: intrinsic Due to fake tau’s W+jets, bbbarμ jets

  11. tt  bWbH±  blνbτν (cont’d) EVENT SELECTION: • one isolated high-pT lepton within by t-lepton within |η|<2.5 ! TRIGGER ! This lepton originates from semi-leptonic decays of the second top quark • one identified tau-lepton (EXCELLENT tau-id needed) • at least 3 jets wit pT > 20 GeV and |η|<2.5 • 2 b-tags ! • also ΔΦ cut (mainly to remove bbbar, W+jets bgnd) Reduction of the bgnd from W+jets and bbbar production to the level below ttbar level. TDR 9.1.5, also see Marjorie’s talk Tau-ID trivia: Trigger:combination of LVL1 multi-jet trigger, ETmiss + tau, ETmiss+jet • Narrow calorimeter clusters  well collimated jets as compared to QCD jets • ~78% of hadronic τ-decays has exactly one charged track • Soft leptons (direction of the lepton ~ tau) Trigger: hadronic tau-trigger LVL1 Calo + LVL2 EM iso + LVL3 Pxl iso LVL1: 90% for signal and 6kHz QCD bgd LVL2+LVL3: 40% for signal and e(QCD)=10-3 further improvement with using tracking at LVL3 possible

  12. tt  bWbH± blνbτν (cont’d) The single-prong, e.g.   ± (12.5%), hadronic  decays from H± are harder than the ones produced in W± decays due to spin configuration (very useful against bgnds: ttbar, Wt, W+jets and QCD) This effect is very useful for larger Higgs masses. The cuts select mainly the right-handed tau-leptons from charged Higgs decay with respect to W-decay because the products are harder in pT. R-handed L-handed Significance of the H± signal: Significance = excess of tau’s produced / error (stat.  syst.) # of events observed from MSSM production of (one or more) Higgs bosons and of WW pairs + # of events from SM WW pair production (using universality from W e/μ mode. Includes error from fake tau’s in MSSM and SM

  13. tt  bWbH± blνbτν : Results In 30 fb-1, mH = 130 GeV, tanβ = 5., the excess of τ-leptons is 1,200; 2,500 τ-leptons come from W-decays and 3,400 are fake τ-leptons

  14. “Hadronic channel” - Signal σ ~ 12.6 pb, tanβ = 30, M(H) = 127 GeV/c2 - in this channel, it is possible to reconstruct Higgs mass out of the transverse mass distribution, because two FS neutrino are in the same hemisphere - Counting experiment - # of events after the final cut compared with the null hypothesis (bgnd only) - statistical significance = S / √B tt  bWbH± bqq‘bτν Catherine Biscarat, Mireia Dosil, ATL-PHYS-2003-038 BACKGROUNDS: CUTS: tt  bWbW bqq‘bτνσxBR = 57.2 pb QCD bgnd: topology very different (huge σ ~ 55 mb) Z/γ and W bgnd: large combined σ ~ 17 nb, W/Z produced tau-jets in their decays • 2 b-jets • 2 light-jets (from W decays) • 1 tau-jet (hadronic tau decay) • large MET • single-prong tau-decay story for W and charged Higgs • (Jet+Etmiss) OR (+Etmiss) trigger • Top mass reconstruction (|mjjb-mtop| < 40 GeV) • Higgs mass can be reconstructed by means of MT Again: Excellent tau-ID + good MET measurement

  15. ATLAS all MSSM Higgses(10 fb-1) Now covered tt  bWbH± bqq‘bτν (cont’d) • MT cut and pT cuts very effective against irreducible background • MT distribution for SM kinematically constrained to be below mW

  16. tt  bWbH± blνbcs Kétévi Assamagan ATL-PHYS-99-013 • Searches performed in a low tanβ region • Higgs masses between 110 and 150 GeV • Extraction of the peak in mjj distribution • seems to be difficult • ttbar events are required to have: • one isolated high-pT lepton within • tracker acceptance, it actually • triggers the experiment • two b-tagged jets with pT > 15 GeV, • |η| < 2.5, VETO on an additional jet • at least two non-b central jets within • |η| < 2.0 for the H± cs reconstruction • VETO on any extra jet above 15 GeV • in the central region. H± cs mH = 130 GeV tanβ = 1.5 ∫Ldt = 30 fb-1 The peak sits on a tail of the Wjj distribution from ttbar events which decay mainly via a Wb.

  17. M(H±) > 180 GeV(above mtop+mb)

  18. gb tH±, H±  tb, t  blν Kétévi Assamagan ATL-PHYS-99-013 H+  tb EVENT SELECTION: • one isolated high-pT lepton within by t-lepton within |η|<2.5 ! TRIGGER ! • three b-tagged jets with pT > 30 GeV, |η| < 2.5 and a VETO on additional jet • at least two non-b jets for the Wjj reconstruction of the other top quark • both top-quark masses reconstructed inside a window • one of the top-quarks to be matched with the remaining b-jet for the reconstruction of the peak in the mbb distribution from H± tb decay Advantage: BR~80% Disadvantage: Large irreducible background At the beginning: S/B ~ 1:100 3 b-tagged jets: S/B ~ 1:20 Acceptance: 2.5% (5.1%) for mH=200(500) GeV After the selection:70% ttb events, 30% ttj events comparable results to ttH, Hbb Wjj resolution ~12.5 GeV tjjb resolution ~10.0 GeV The mass resolution is not as good as it might be expected from the reconstruction of other multi-jet resonance channels. If only the true H±tb combinations were taken  the resolution would be σH ~ 17 GeV ATLAS

  19. improvement in the signal to bgnd ratio wrt H+tb channel (large combinatorial bgnds) gb tH±, H±  τν, t  bqq‘ H+  tn Kétévi Assamagan et al. ATL-PHYS-2000-031 EVENT SELECTION: • one hadronic t-jet, pT > 30 GeV, within |η|<2.5 • at least three not-τ jets, pT > 30 GeV, one of these jets must be a b-tagged jet with |ηb| < 2.5 • W from associated top quark is reconstructed and |mjjb-mtop| < 25 GeV • raise the pT(tau) cut to more than 100 GeV – ’polarization story’, W needs a boost, charged Higgs does not • to optimize the S/B ratio, missing pT > 100 GeV (MT calculation) BGNDS: QCD, W+jets, single-top production, Wtb, ttbar (Wjj, other Wτν) Almost free of irreducible bgnds !!! mH± can be extracted from MT distribution with likelihood method: overall precision from 1.3% at mH±=226 GeV to 3.1% at mH±=511 GeV for 100 fb-1 ATLAS

  20. MSSM Higgs Discovery Potential (i) Assuming SUSY particles are heavy • Plane fully coveredwith 30 fb-1 • 2 or more Higgses observable in large fraction of plane •  disentangle SM / MSSM 5s contours Main channels: h gg, tth  ttbb MA > 100 GeV any tanb A/H tt, mm large tanb Htn, tb MA < 130 GeV any tanb MA>180 GeV large/small tanb

  21. MSSM Higgs Discovery Potential (ii) Large fraction of plane explored already after ~ one year In the intemediate tanβ region only the SM-like h0 isobservable 5s contours

  22. Properties

  23. H± Mass and tanβ Determination Charged Higgs: parameter measurements ATLAS analysis tanβ determination mass determination From transverse mass in H τν case From invariant mass in H tb case Precision dominated by statistics. Method: maximum likelihood or fit of signal+bgnd Systematics: bgnd rate, bgnd shape and energy scale Can be determined from rates only. σxBR ~ tan2 β for large tanβ Precision limited by uncertainties in luminosity and systematics.

  24. Summary Charged Higgs 5σ contour with 30 fb-1 • Most of MSSM parameter space covered with little luminosity (10 fb-1) • Sensitivity to heavy MSSM Higgs dominated by τ in FS • Little sensitivity to “intermediate region” in tanβ with SM decays • SUSY decays (?) • H± (mH±>mtop): covers the discovery potential in the high tan range • H± (mH±<mtop): the hadronic channel (Wqq’) fills the ‘hole’ around tan10 already after the 1st year (10 fb-1) goal is to extend coverage for intermediate tanβ Coverage established so far... …but more ideas on the way… tanβ=5 * gg  tbH+, H±SUSY for moderate tanβ * even studies of H± and extra dimensions CMS is looking at it…

  25. Additional slides…

  26. 4 Higgs observable 3 Higgs observable 2 Higgs observable 1 Higgs observable Observability of MSSM Higgses 5s contours Here only SM-like h0 We may be unlucky, that even if we do find a light Higgs, we will not be able to tell if it is SM or MSSM

  27. Coverage… Coverage established so far...... but more ideas on the way.... * gg  tbH+ , H+ SUSY for moderate tan b * gluinos/squarks  χχ +X  H+( tn) + X seems promising for moderate tan b * even studies of H+ and extra dimensions CMS is looking at it… goal is to extend coverage for intermediate tanβ tan b =5 tan b =40

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