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Charged Higgs Prospects with CMS

Charged Higgs Prospects with CMS. Prospects for Charged Higgs Discovery at Colliders Uppsala, 13-16 September 2006. R. Kinnunen Helsinki Institute of Physics. Contents. - Introduction CMS full simulation Searches for the light charged Higgs bosons with the H ± -> tn decay

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Charged Higgs Prospects with CMS

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  1. Charged Higgs Prospects with CMS Prospects for Charged Higgs Discovery at Colliders Uppsala, 13-16 September 2006 R. Kinnunen Helsinki Institute of Physics R. Kinnunen Helsinki Institute of Physics

  2. Contents • - Introduction • CMS full simulation • Searches for the light charged Higgs bosons with the H± -> tndecay • channel in the tt events • Searches for the heavy charged Higgs bosons: • with the H± -> tn decay channel • with the H± -> tb decay channel • - Other possible search channels R. Kinnunen Helsinki Institute of Physics

  3. Production and decay channels • Production of the H±at the LHC mainly through the processes • tt, t ->bH±for mH+ < mtop – mb • gb -> tH±and gg -> tbH±for mH+ > mtop Main decay channels: H± -> tn, H± -> tb, H± -> Wh, H± -> c0c± R. Kinnunen Helsinki Institute of Physics

  4. CMS full simulation • GEANT4 based detector simulation (OSCAR) • Full event reconstruction (ORCA) • All predictions include the pile-up corresponding to the low • luminosity of 3x1033cm-2s-1 • In the following expectations only for low luminosity are shown R. Kinnunen Helsinki Institute of Physics

  5. Search for light charged Higgs bosons Signal process defined as gg -> tt -> W±H±bb->lntnbb, l = e or m Minimum of BR(t->bH±) at tanb ~ 6 Signal generation with PYTHIA BR(H± -> tn) with HDECAY t decays with TAUOLA For mH+ = mtop the off-shell contribution included with the process gb->tH± and compared to the results from gg -> tbH± - Generation of the gb -> tH± and gg -> tbH± processes with PYTHIA R. Kinnunen Helsinki Institute of Physics

  6. Backgrounds Main backgrounds from tt and W+3 jet production with a jet faking hadronic tdecay, 3 final states from tt: pp ->tt->W+W-bb, W+->t+n, W-ln pp ->tt->W+W-bb, W+->jj, W-ln pp ->tt->W+W-bb, W+->ln, W-l’n Generation of tt events with PYTHIA, cross section normalization to 850 pb W+3jets,Wln, generated with MadGraph, ET > 20 GeV, |h| < 2.5, DRjj>0.5 Wt,W1ln, W2tn or qq, generated with TopRex, normalization of sxBR to 1.8 pb tq+tb,t->Wblnb, generated with TopRex, normalization of sxBR to 78.1 pb Wbb, Wln, generated with TopRex Zbb, Zll, generated with MadGraph R. Kinnunen Helsinki Institute of Physics

  7. Search strategy, selection chain Event selection l one lepton passing the Level-1 and HLT triggers l at least 3 jets with ET > 40 GeV l exactly one b jet tagging with track counting method and impact parameter measurement Efficiency for mH+ = 140 GeV : signal 47%, tt background 45%, W+3jets 16% l one identified t jet, ET > 40 GeV l Ql x Qt = -1 l Missing ET > 70 GeV R. Kinnunen Helsinki Institute of Physics

  8. Offline t identification Identification starts fromt canditates provited by the L1+HLT trigger • Definition of t identification variables: • Matching cone Rm around the jet direction for searching • the leading track • Signal cone Rs around the leading track • Isolation cone Ri around the signal cone For this channel: lRm = 0.1, Rs = 0.07, Ri = 0.4 with veto on tracks with pT > 1 GeV in the isolation cone lECAL isolation for t jet: SETcell (0.13<DR<0.4) < 5.6 GeV, DR defined around the jet direction lElectron contamination suppressed with a cut on maximal HCAL cell (ET > 2 GeV) inside the jet cone l pleading track / Et > 0.8, to exploit the opposite t helicity correlations in in the H± -> tn and W± -> tn decays, leading to harder pions from H± -> tn Efficiency: signal 11-15%, tt->WWbb -> bbt+nln 5%, W+3jets 1%, tt->WWbb -> bbl’n’ln 2% R. Kinnunen Helsinki Institute of Physics

  9. Arbitrary normalization Examples of event selection variables Arbitrary normalization Arbitrary normalization Missing ET > 70 GeV cut can suppress only the W+3jet background tt events 50-60% W+3 jets ~40% Signal/background difference in the hadronic channels due to t helicity correlations R. Kinnunen Helsinki Institute of Physics

  10. Selection efficiencies for signal and backgrounds • Other signal sources in tt events, like H± ->tb,cs,su,cb and H±->tn,t->lnn,W->jj, also studied and the contribution is found to be small • l Backgrounds from ofher sources (Zbb, Wbb) negligible • l Good agreement for the events from tt + gb->tH±and gg->tbH± at mH+= 170 GeV R. Kinnunen Helsinki Institute of Physics

  11. Estimation of systematic uncertainties Measurement uncertainties affecting the event selection efficiency and methods for their measurement Expectations for 30 fb-1 R. Kinnunen Helsinki Institute of Physics

  12. For the estimate of the tt uncertainty the theoretical cross section is used with a total theoretical uncertainty of 5.6% from PDF uncertainty 2.5% and scale uncertainty 5% (luminosity uncertainty 5%): • W+3 jet background uncertainty is assumed to be measured from data. • For an estimate a signal-free ”area” is defined with selection cuts similar to • the signal selection with: • - one lepton (Level-1 and HLT) • - 3 non-b jets • - no t jets • including pixel isolation for an electron to avoid QCD background • substraction of the tt contribution R. Kinnunen Helsinki Institute of Physics

  13. R. Kinnunen Helsinki Institute of Physics

  14. Expected H± discovery reach from gg -> tt -> W±H±bb->lntnbb in mhmax scenario with m = 200 GeV R. Kinnunen Helsinki Institute of Physics

  15. Searches of heavy Charged Higgs bosons with H± -> tn in the associated production Fully hadronic events selected with the t-> hadrons + nand t -> qqb decays to exploit thelicity correlations andto reconstruct the H±transverse mass with missing ET from H± -> tn Event genaration with the gg -> tbH± process - allows predictions close to the tt threshold l Signal generation with PYTHIA ltdecays with TAUOLA l Normalization to the NLO cross section by T. Plehn et al. l normalization of BR and MSSM mass relations with FeynHiggs R. Kinnunen Helsinki Institute of Physics

  16. Backgrounds, generator and normalization tdecays with TAUOLA R. Kinnunen Helsinki Institute of Physics

  17. Event selection • Trigger: • Level-1: tjet, ET > 93 GeV • HLT: Missing ET > 67 GeV, • primary vertex reconstruction with pixel lines, • regional reconstruction inthe full tracker around the Level-1 t jet • pT > 25 GeV for the leading track, isolation in a cone around the leading track • Offline analysis: • Veto on isolated leptons from W->ln to ensure missing ET fromH± -> tn lepton identification with tracker isolation, andwith ECAL/track matching, shower shape, ECAL/HCAl ratio for electrons, ”BR(W->mn)” = 8.9%, ”BR(W->en)” = 7.9% with good purity • l Identification of one hadronict jet • l Missing ET > 100 GeV • l W and top mass reconstruction • l tagging of one b jet • l veto on addional central jets with ET > 25 GeV • l transverse mass reconstruction from the t jet and Missing ET R. Kinnunen Helsinki Institute of Physics

  18. Off-line t identification Hadronic t decay modes found after trigger: • -> p + np0 + n dominates at this level -> Calorimeter t reconstruction used Energy flow algorithms under study in CMS for the possibility for a more precise tracker reconstruction of the hadronic t decay Offline tidentification: - jet reconstruction in the direction of the triggeredjet, ET > 100 GeV • leading track within DR < 0.1 around the jet direction • small signal cone around the leading track, Dr=0.04 • one or three tracks in the signal cone • isolation of the signal cone in 0.04<DR<0.4 • addional quality cuts for the leading track: transverse impact parameter < 0.3 mm • and at least 10 hits in the tracker (signal efficiencies ~95%) • - ET of maximal HCAL cell in the jet > 2 GeV to remove electron contamination • pleadingtrack/Etjet > 0.8, exploits the t helicity correlations R. Kinnunen Helsinki Institute of Physics

  19. t selection efficiencies Helicity correlations in H± ->tn and W± ->tn: harder pions from H± -> tn than from W± ->tn in the t ->pn decay and in the decays through longitudinal compoments of r and a1 mesons Distributions affected by the trigger selection! t-selection efficiencies including pre-selection, trigger and off-line QCD multi-jet event: generation with 170<pt<380 GeV, no trigger simulation R. Kinnunen Helsinki Institute of Physics

  20. Top mass reconstruction and b tagging Minimization ofc2 = ((mjj –mW)/sW)2 + ((mjjj –mtop)/stop)2 with sW = 10 GeV, stop = 17 GeV, from all hadronic jets with ET>20 GeV, no mass window used for the reconstructed W mass ~20% probability for pTb(ass) > pTb(t->bqq) Due to the jet assignment problem any of the 3 jets tagged with a probabilistic secondary vertex method discriminator > 1.5 and Etjet > 30 GeV Efficiency for 140 < mtop < 210 GeV+one b jet: 25% signal (mH+=200 GeV), 1.2% W+3 jets R. Kinnunen Helsinki Institute of Physics

  21. Transverse mass reconstruction mT = (2 ETt jet ETmiss (1 - Df(t jet, ETmiss))1/2 Transverse mass distributions for the signal and background with all selection cuts with pTHiggs > 50 GeV • ~1.4 tt events at large mT, with good missing ET measurement and passing track qualitycuts, • are events triggered with a hadronic jet (fake t signal) • can be suppressed requiring strong correlation for the t jet and missing ET • with pTHiggs > 50 GeV (signal efficiencies > 84% ) R. Kinnunen Helsinki Institute of Physics

  22. Transverse mass reconstruction Signal area may be defined with a cut in Df(t jet, ETmiss), but mT(t jet, ETmiss) > 100 GeV used in this study R. Kinnunen Helsinki Institute of Physics

  23. Selection efficiencies and number of events for 30 fb-1 tanb = 30 Uncertainty due to MC statistics and factorization procedure • QCD background estimation with the full selection chain • estimate neglecting correlations between Missing ET and t selection cuts • no trigger simulation • t selection applied on the leading jet • - Negligible contribution from the pT bins below pT < 170 GeV R. Kinnunen Helsinki Institute of Physics

  24. Systematic and MC uncertainties • Two main sources of background in the signal area mT(t jet, ETmiss)>100 GeV: • - tail of the tt and W+3jet backgrounds due to measurement uncertainties • fake t jets, possible in all considered backgrounds • lThe tail of the tt and W+3jet backgrounds can be measured from data exploiting the • W+3jet, W->mn events with large rate and precise muon momentum measurement • l Fake t rate may be determined with the help of the g+jet events These measurements not yet done, the uncertainty of the dominant tt background estimated on basis of event selection efficiency and the cross section: Uncertainty in the event selection efficiency 3% obtained from the tt events with variation of the jet and missing ET scales within the expected uncertainties Including the experimental uncertainties (t identification 8%, b tagging 5%, luminosity 5%) and the tt cross section uncertainty of 5.6%: l Systematic uncertainty on the tt (and Wt) backgrounds 11% l For W+3jet the present MC uncertainty (~100%) strongly dominates Including systematic and MC uncertainties total background in the signal area mT> 100 GeV: 1.7 ± 1.0 events R. Kinnunen Helsinki Institute of Physics

  25. Discovery potential R. Kinnunen Helsinki Institute of Physics

  26. R. Kinnunen Helsinki Institute of Physics

  27. Signal and Background Simulation Signal simulation with PYTHIA for both processes gb -> tH± 3b selection gg -> tbH± 4b selection Normalization to NLO gb -> tH± cross section Background generation: For 3b selection ttjj with MadGraph/MadEvent For 4b selection ttbb with CompHEP ttjj with CompHEP problem of double counting of b’s b’s from gluon splitting vetoed in the ttjj background Detector simulation for the 3b selection with parametrized fast simulation FAMOS R. Kinnunen Helsinki Institute of Physics

  28. Event reconstruction and selection l L1 + HLT single muon trigger l muon reconstruction and isolation with dicriminator method for muons from t -> W->m, pT > 20 GeV/c l b -jet identification with likelihood-based secondary vertex algorithm 3 jets with discriminant > 1 Event selection: l at least one muon with l at least 5 (6) jets for the 3(4)b selection with ET > 25 GeV l at least 3 (4) b-tagged jets for the 3(4)b selection with ET > 25 GeV l Kinematic fit in the top system with - both W mass constraints - both top mass constraints - jet and muon resolutions as function of pT - transverse and longitudinal momentum of neutrino taken from fit S/B ratio after selection ~1% for mH+ = 300 GeV R. Kinnunen Helsinki Institute of Physics

  29. Jet association Likelihood ratio S/(S+B) for each variable, S=correct associations, B= wrong associations Best possible jet association chosen with the highest value of a combined Likelihood ratio R. Kinnunen Helsinki Institute of Physics

  30. Mass reconstruction R. Kinnunen Helsinki Institute of Physics

  31. Background suppression Observables for background separation: - PT of the softest q jet from the W decay - c2 probability of the kinematic fit, - b-jet discriminator for the b originating directly from the H± - the ratio of the ET of the sixth over the fifth jet Statistical significance as a function of combined Likelihood ratio for signal-background separation, optimized for each mass point R. Kinnunen Helsinki Institute of Physics

  32. H± Observability in the H± ->tb decay Mistag uncertainty for b not estimated yet, assume 0%, 1% and 3% Similar analysis performed for the 4 b-tag channel 3 b-tag channel 4 b-tag channel R. Kinnunen Helsinki Institute of Physics

  33. Other possibilities for H±searches H± -> Wh, h -> bb decay channel in gb -> tH± production, with the final state of one isolated lepton, 3 b jets and 2 non-b jets Fast simulation study at mH+ = 180 GeV, tanb = 2.5 with full reconstruction of the event (leptonic and hadronic W, associated top and H±) Main event reconstruction problem: correct jet association difficult No discovery even with high luminosity and assuming known mh R. Kinnunen Helsinki Institute of Physics

  34. gg -> tH±,H± -> ci+cj0 -> 3 leptons + X Fast simulation study with 3 sets of parameter values in MSSM: Set A: M2 =210 GeV, m= 135 GeV, mlR = 110 GeV, mg = 800 GeV, mq = 1 TeV Set A: M2 =280 GeV, m= 150 GeV, mlR = 130 GeV, mg = 900 GeV, mq = 1 TeV Set A: M2 =300 GeV, m= -150 GeV, mlR = 150 GeV, mg = 1 TeV, mq = 1 TeV Backgrounds: tt, ttZ,ttg*,tth, neutralino and chargino pair production, squark and gluino production high luminosity expectations • Event selection mainly by: • - 3 isolated leptons, pT>20,7,7 GeV • - Reconstruction of the associated hadronic top • Missing ET > 40 GeV Small m, light sleptons favoured, dominant decay modes in the 5s region of Set A: H± -> c1+c20, c2+c20, c1+c40 c20-> slepton+lepton->llc10 c1+-> sneutralino+lepton -> nlc10 Discovery in an interesting region of medium tanb but for a limited area of parameter space R. Kinnunen Helsinki Institute of Physics

  35. Discovery Potential for charged Higgs Bosons with full simulation, including systematic uncertainties R. Kinnunen Helsinki Institute of Physics

  36. Conclusions The H± -> tn decay channel in the tt production and in the associated gg -> tbH± production remain discovery channels with large parameter space reach for the charged Higgs bosons with full simulation and reconstruction of the CMS detector response • For H± ->tnin the tt production inclusion of systematic uncertainties results in a decrease of the mass reach by 5-10 GeV • For H± ->tnin the fully hadronic channel at mH+ > mtop suppression of fake t signals in the backgrounds, including the QCD multi-jet production, requires • strong t isolation • high quality measurement for the leading track • large Missing ET cut even for the low mass range (due to QCD multi-jet background) • Minor reduction of the discovery potential for the gg -> tbH±, H± -> tn • channel as compared to the earlier fast simulation results • lNo discovery with H± ->tb at low luminosity R. Kinnunen Helsinki Institute of Physics

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