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Search for a charged Higgs in H + cs using 4.7 fb -1

Search for a charged Higgs in H + cs using 4.7 fb -1. A. Martyniuk a , P. Miyagawa b , M. Owen c , O. Trifis c , V. Chavda c , and U.K. Yang c a: University of Victoria b: University of Sheffield c: University of Manchester Higgs Meeting, August 27, 2012.

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Search for a charged Higgs in H + cs using 4.7 fb -1

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  1. Search for a charged Higgs in H+cs using 4.7 fb-1 A. Martyniuka, P. Miyagawab, M. Owenc, O. Trifisc, V. Chavdac, and U.K. Yangc a: University of Victoria b: University of Sheffield c: University of Manchester Higgs Meeting, August 27, 2012 Thanks to the Editorial Board: Michel Vetterli (Chair) Martin zur Nedden, Wouter Verkerke, James Ferrando

  2. Introduction • A charged Higgs boson is predicted by the Beyond SM: Two Higgs Doublet Model: H0, h0, A0, H± • Charged Higgs productions from top quark decays • Huge top production, focus on H+cs at low tanb • Complementary to H+tn at high tanb e/m W+ b-jet ν jet W/H- b-jet jet

  3. Analysis Overview • Semi-leptonic tt sample • Dijet mass c2 fitter e/m W+ b-jet ν jet W/H- b-jet jet • Likelihood Fit, Br(tH+b): • Discovery or 95% Limits

  4. Analysis History • Previous analysis with 35 pb-1 data (≥ 1 b-tag), comparable to the Tevatron limits ( ATL-CONF-2011-127, ATL-COM-PHYS-2011-130) • Updated analysis with 4.7 pb-1 (2011 full data) • High-pt lepton with 4 jets (at least 2 b-tag) • Single lepton trigger samples • Use the Top group selection cuts and have a good agreement • Lep Pt>25 (e), 20 (m), Jet Pt>25, MET> 35(e), 20(m), MV1 w>0.6 • The list of the full event selections cuts is in the backup slide • Supporting document • ATL-COM-PHYS-2012-660 • The updated analysis has a conditional approval in June, 2012 • Issues with systematic • Issues with fit stability

  5. Analysis Essential 1 • A dijet mass c2 fitter: lepton plus 4 jets • Improved the dijet mass dist. by reconstructing whole ttbar event • Constrain W(e/m) and top quarks masses to be the PDG values, by floating jet/lepton energy within their resolutions • The 5th jet can be replaced as a W daughter jets with any of the two untagged 3rd, 4th jets • Remove poorly reconstructed events with c2<10 Before Fitting After Fitting

  6. Analysis Essential 2 • Signals and background templates • Seven H+ signal templates from 90 to 150 GeV by 10 GeV step • SM ttbar template • Non-ttbar template (10%): • Single top, W/Z+jets, QCD, • and diboson

  7. Analysis Essential 3 • Set limits on the branching ratio to charged Higgs boson using the frequentic procedure • A likelihood function is define as where ni: observed events, ni: expected events in each bin • Limits are calculated on a test Statistics qb based on a profile Likelihood ratio The exp. events of ttbar bkg and H+ signal as BR(tH+b)

  8. Issues Raised in the Higgs Approval meeting and by the Edboard • Missing contributions in the limits • b-JES/c-JES syst. • Mtop syst. • Updated Stop t-ch. norm • Implementation of the syst. band in the kinematic distributions • Check the output nuisance parameters and their correlations • (N-1) limits to show the syst. effect of each item • Limits without a constraint on the s(ttbar) Limits presented in the approval meeting in June

  9. Systematic

  10. Updates • Missing syst. contributions (b-/c-JES, Mtop, proper Stop t-ch. norm.) are included. Their contributions are small(done) • After ICHEP deadline passed, we decided to update our analysis • Use the most updated JES calibration and it’s uncertainty ( tag 00-05-09):  lower eff. for Njet>=4 cut • Use the updated luminosity with small error: 4.66 /fb with 1.8% (old: 4.71/fb with 3.4%) no change in the data, but the bkgd prediction based on the MC is reduced by 1.2% • Implementation of the syst. band the kinematic distributions (done) • Check the output nuisance parameters and their correlations (done) • Limits without a constraint on the s(ttbar) (done) • (N-1) limits to show the syst. effect of each item (done)

  11. Data vs Predictions old new data old new SMttbar

  12. Data vs Predictions

  13. Updated dijet mass dist.

  14. Results • The fit results are consistent with null Higgs hypothesis Stat. Only

  15. Results on the Nuisance Parameters mH=90 GeV mH=110 GeV

  16. (N-1) Limits? • The effect of the individual syst.? • The only one syst. Item is removed in the fit, “(N-1)” limit • Basically, the (N-1) limits are close to the N limits due to the correlations with other parameters

  17. Correlations: nuisance parameters mH=90 GeV • Groups of the correlated systematic • JES, Mtop, bJES: c • bTag, s(ttbar) • Gen, I/FSR, PS and JER

  18. (N-x) Limits • A group of the correlated parameters (x) is removed in the fit to check the effect of their syst. on the limits • The (N-x) limits look reasonable

  19. The effect of the s(ttbar) constraint? • In the current fit, s(ttbar) is constrained with +7%/-9% uncertainties • What if we remove this constraint? basically 2 parameter fitting: Br(tH+b) and s(ttbar) • The limits are not changed • The resulting cross sections are consistent with the SM

  20. Conclusions • The full 2011 data (4.7 fb-1) have been analyzed to search for a charged Higgs from top quark decays. • The results are consistent with null Higgs hypothesis • The 95% limits on Br(tH+b) are set between 5% to 1%, depending mHare improved by a factor of 5 to 10, with respect to the current best limits in csbar channel • The limits, equivalent to the limits from the three combined tau channels. • We plan to publish these results

  21. Backup Slides

  22. Event Selection • Semi-leptonic channel: e/m plus at least 4 jets (2 b-tag) • Use the Top group selection cuts and have full agreement: acceptance challenge • Cuts are: • One el with ET> 25 GeV & |η| < 2.47, with a veto (1.37 < |η| < 1.52), OR one mu with pT> 20 GeV and |η| < 2.5 with single lepton triggers (EF_e20_medium,EF_e22_medium, EF_mu18, EF_mu18_medium) • Remove events tagged as e-mu overlap • Require a primary vertex with at least five tracks • MET > 35 GeV (el), OR MET > 20 GeV (mu) • Mt(W) > 25 GeV (el) OR MET + Mt(W) > 60 GeV (mu) • ≥ 4 jets with ET> 25 GeV and |η| < 2.5 and |JVF|>0.75 • Events with loose bad jets with pT> 20 GeV are rejected • ≥ 2 jet tagged with MV1 weight > 0.601713

  23. Background estimations • SM ttbar (~90% of the total bkgd) • Use MC@NLO sample for shape and normalization with NNLO cross section • W+jets, Wbb/cc+jets, Wc+jets (~3.6% of the total bkgd) • Use ALPGEN interfaced with Herwig samples for shape and normalization • Normalized with K*cross sections plus the SFs derived from the Top W+jets group based on the W+/W- charge asymmetry in the data • Single top (~3.7% of the total bkgd) • Use MC@NLO sample for Wt and s-channel, but AcerMC for t-channel normalized with NNLO cross section (also shape) • Multi-jets (~2.5% of the total bkgd) • Use anti-electron data-driven method provided by the Top fake group (normalization)

  24. Background template

  25. Updated PS systematic • Powheg plus Herwig vs Pythia? • With Pythia AMTB1 tune: 11% difference in acceptance, disfavored by the jet shape data. • New PS syt. with Pythia Perugia 2011 C tune:3% difference in acceptance • The effect due to the PS on the limit is very minimal. Pythia Perugia 2011 C tune Pythia AMBT1 tune

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