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Final results on ttH H   +  -

Final results on ttH H   +  -. Akihiro, ITO, Reisaburo TANAKA O kayama University Shoji ASAI, Junichi TANAKA ICEPP, University of Tokyo Junichi KANZAKI KEK Many thanks to Lidija ZIVKOVIC (Weizmann) A TLAS Higgs Working Group Meeting, September 22, 2003. Contents.

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Final results on ttH H   +  -

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  1. Final results on ttH H+- Akihiro, ITO, Reisaburo TANAKA Okayama University Shoji ASAI, Junichi TANAKA ICEPP, University of Tokyo Junichi KANZAKI KEK Many thanks to Lidija ZIVKOVIC (Weizmann) ATLAS Higgs Working Group Meeting, September 22, 2003

  2. Contents • ttH (H+-) analysis •  tag algorithm • ATLFTAU • Summary Final Results on ttH (H->tau+tau)

  3. 1. ttH (H+-) analysis • Physics Motivation: direct determination of top-Yukawa coupling in the mass range MH=[100, 130]GeV/c2. Complementary to Hbb. • Signal • Small cross section (Br  40fb @MH=120 GeV/c2) • ttH  WbWb … 9 different modes, followings are analyzed. • lb+jjb +l+h channel … same charge di-lepton ll  Br=14% • lb+jjb + h+h channel … single lepton Br=13% • lb+jjb +l+l channel … tri-lepton Br= 4% • lb+lb+l+h channel … tri-lepton Br= 2% • lb+lb+h+h channel … di-lepton Br= 2% • Backgrounds • HUGE tt ! (ttH)Br(H) / (tt)  10-4, ttW • ttZ, ttWW, ttH(HWW) … irreducible backgrounds. Key issue: -tag, fake-jet rejection Israel 5 modes Japan 2 modes Final Results on ttH (H->tau+tau)

  4. top-Yukawa coupling in ttH(Hbb,+-,W+W-) Athens Physics Workshop (R.T.) L = 30 fb-1 Preliminary Hbb poor S/N gttH/gttH HW+W- 2030% H+- (Weizmann) MH [GeV/c2] Final Results on ttH (H->tau+tau)

  5. 2 issues •  tag algorithm ATLFTAU v.s. Weizmann • ATLFTAU: parametrized 50% fixed efficiency • Weizmann: inspired by TDR algorithm. • Is ttH(H->  )  lb+jjb + h+h possible? Final Results on ttH (H->tau+tau)

  6. 2.  tag algorithm • Issue:  tag algorithm optimization for ttH ATLFTAU … 50% fixed efficiency for low Pt taus is not good. Leads to unreasonable low rejection factor. • Emulated Weizmann tau identification method • Rj-track < 0.07 (distance between jet and nearest track) • Ntrack = 1 or 3 (# of tracks with PT>5GeV/c in DR = 0.07) • PT(track) > 5GeV/c (PT of track nearest to jet) • I < 0.03 I = { ET(0.4) – ET(0.2) } / ET(0.2) • PT(-jet) > 20GeV/c • Ncell < 6 (# of cells in jet, COMMON/ATLFEVENT/ K(nj, 3) ) • Observed good agreements on these variables. Though differences in PT(track) and I distributions. Final Results on ttH (H->tau+tau)

  7. E.Gross, June 25, 2003@Higgs WG t tag efficiency and jet rejection mH = 120 GeV 50% algorithm real t fake t pT-t-jet Final Results on ttH (H->tau+tau)

  8. High Level Trigger Lepton PT > 20GeV/c, |η| < 2.5, Nlepton≥ 1 Jet PTj1 > 35GeV/c, PTj2 > 25GeV/c |η| < 4.5, Njet≥ 2 b-jet ( efficiency = 70%) PT > 20GeV/c, |η| < 2.5, Nb-jet≥ 2 -jet PT > 20GeV/c, |η| < 2.0, N-jet≥ 2 Mass windows 60 < Mqq < 90 GeV 150 < Mbjj < 195 GeV 50 < M-jet,-jet < 120 GeV Missing ET > 25GeV Φ( , missing ) < 1 opposite charge of -jet B-tag efficiency 70% Weizmann cut on lb + jjb + h + h Final Results on ttH (H->tau+tau)

  9. ATLFAST, ttH MH=120GeV, Low lumi. Labeled t-jet Japan Other jet Rj-track< 0.07 Ntrack= 1 or 3 PT> 5 GeV/c (GeV) Israel Final Results on ttH (H->tau+tau)

  10. ATLFAST, ttH MH=120GeV, Low lumi. Japan Cone R<0.3 I< 0.03 PT> 20 GeV/c N5 (GeV) Very powerful cut ! Israel Final Results on ttH (H->tau+tau)

  11. Results with Weizmann tau ID Ncell Ncell ttHlb+jjb + h+h MH=120GeV, Low lumi. 100fb-1 Remaining difference YPAR(93) - fraction of tau-jet in a cone Rtau-jet Japan: default 0.9 Israel : 0.0 (optimistic?) Final Results on ttH (H->tau+tau)

  12. Signal t-jet (GeV) Think about ET cuts in cells ? ETcell > 0.5GeV (noise & pile-up) signal N4 ET>0.5GeV tt ttHlb+jjb + h+h MH=120GeV, Low lumi. 100fb-1 Final Results on ttH (H->tau+tau)

  13. Without ETcell cut With ETcell cut Number of events for 100fb-1 (percentage wrt previous cut) Final Results on ttH (H->tau+tau)

  14. 6 times! 3. ATLFTAU Atlftau Results • Reasons • Fake t-jet charge Final Results on ttH (H->tau+tau)

  15. Generator • ATLFAST parameter YPAR(93) : fraction in a cone R_tauj for tau-jet Final Results on ttH (H->tau+tau)

  16. Qt1*Qt2 ttH tt Israel • Drops the ttH signal. • But also artificial cut on tt. • Unphysical effect. Explains factor 3 difference tt ttH Japan Final Results on ttH (H->tau+tau)

  17. ATLFAST Number of events for 100fb-1 (percentage wrt previous cut) Now identical condition YPAR(93)=0.0, Φcut good agreement. Final Results on ttH (H->tau+tau)

  18. 4. Summary • Compared two analyses on ttH(H) • Tau hadronic mode: lb + jjb + h + h • -tag algorithm • ATLFTAU (50% eff. Fixed) - Unreasonable at low Pt. Problematic for ttH. • Weizmann algorithm - Ncell is a powerful parameter for tt rejection but pile-up and noise should be taken into account. • Full simulation with noise&pile-up under study. • ATLFAST (parametrized ATLFTAU) • Good agreement between Japan and Israel results now. • Discrepancies due to -jet charge assignment ,YPAR(93),Φ. • These are not critical for our final results … Final Results on ttH (H->tau+tau)

  19. Our Results for Athens L=300 fb-1 MH=115GeV/c2 ttH (H+-) t( l b ) + t( l b ) + ( h  ) + ( l   ) t(l b ) + t(jjb) + ( h  ) + ( l   ) For 2 300 fb-1 S/B = 0.8 S/B = 4.5 (Poisson) t(lb) + t(jjb) +  (h)+  (h) Similar sensitivity as di-lepton channel, but suffers from irreducible ttZ, ttWW …background. Final Results on ttH (H->tau+tau)

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