Physics of Charged Higgs Boson(s) at the LHC

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