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How to Exploit t Polarization in Charged Higgs Boson Searches

How to Exploit t Polarization in Charged Higgs Boson Searches. Prospects for Charged Higgs Discovery at Colliders Uppsala, 13-16 September 2006. R. Kinnunen Helsinki Institute of Physics. Background for t polarization studies.

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How to Exploit t Polarization in Charged Higgs Boson Searches

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  1. How to Exploit t Polarization in Charged Higgs Boson Searches 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. Background for t polarization studies • Amethod to use t polarization to enhance the signal for the • charged Higgs bosons in the H± ->tn decay channel • (in tt and gb->tH± production) was first proposed by • DP. Roy, Phys. Lett. B459 (1999) 607. • The method was applied by the CMS and ATLAS collaborations • in several studies on charged Higgs bosons: • R. Kinnunen, CMS Note 2000/045; • K.A. Assamagan and Y. Coadou, Acta Phys. Polon. B33 (2002)707; • M. Baarmand, M. Hashemi and A. Nikitenko, CMS Note 2006/056; • R. Kinnunen, CMS Note 2006/100 • (only some examples mentioned) R. Kinnunen Helsinki Institute of Physics

  3. H± and t decay modes H± ->tn decay dominates for mH+ < mtop and is large also for mH+ > mtop at large tanb Hadronic t decay modes BR(t ± -> p±nt ) = 12.5% BR(t ± -> r±nt -> p± p0nt ) = 26% BR(t ± -> a1±nt -> p± p0p0nt) = 7.5% 1-prong decay modes ~ 50% 3-prong decay modes ~15% R. Kinnunen Helsinki Institute of Physics

  4. Background suppression in the charged Higgs bosons searches with the H± -> tn decays channel The search channels with H± -> tnare a subject of background from genuine t’s and from hadronic jets faking t’s Hadronic jetsfaking t jets from QCD multi-jet events, from W/Z+jet and tt events can be suppressed with the hadronic tdecay properties; narrow jet in calorimeters and 1 or 3 charged particles in the tracker Mass reconstruction of t, track impact parameter measurements and secondary vertex reconstruction can be used to improve this selection The backgrounds with genuine t’s from tt and W+3jet backgrounds with W->tn can be also efficiently suppressed due to the opposite helicity correlations in the H± -> tn and W± -> tn decays The basic event selection requirements, like large ET for the t-like trigger jet, already exploit the t polarization Selection can be enhanced with special selection cuts R. Kinnunen Helsinki Institute of Physics

  5. Helicity correlations Center of mass angular distributions of t into a p meson or a vector meson (r,a1) in terms of polarization L and T are the longitudinal and transverse polarization states of the vector meson. In the laboratory frame pp,V / pt = Harder tjet for signal with Pt = +1 than for the background with Pt = -1 from the p, rL and a1L contributions, and the opposite from the rT and a1T R. Kinnunen Helsinki Institute of Physics

  6. Helicity correlations Illustration with simple spin arguments for t+ -> p+n formH+ -> t+n and W+ ->t+n: W+ t+ H+ n t+ n l l t+ n t+ p+ p+ n l l R. Kinnunen Helsinki Institute of Physics

  7. Energy charing in the vector meson decays Energy fraction carried by the charged pion in the vector meson decays: r±L,T -> p±p0 and a±1L,T -> p±p0 p0 from D.P. Roy, Phys. Lett. B459 (1999) 607 For r±L and a±1L: Ep± ~ 0 or Ep± ~ Er,a1 for r±T and a±1T: Ep± ~ Ep0 R. Kinnunen Helsinki Institute of Physics

  8. Exploiting helicity correlations in 1-prong t decays Example of helicity correlations in 1-prong t decays in the gb->tH±, H± -> tn signal and in the tt background with fast simulation and calorimeter smearing ETtjet > 100 GeV ETtjet > 100 GeV A hard cut, R1 = pp / pt > 0.8 suppresses efficietly the background from tt, W->tn R. Kinnunen Helsinki Institute of Physics

  9. Helicity correlations in full simulation Search for light charged Higgs bosons with mH+ < mtop in gg -> tt -> W±H±bb->lntnbb, l = e or m All hadronic t decays channels included • one t jet with off-line identification: • ET > 40 GeV • tracker and ECAL isolation • 1 or 3 prongs in the signal cone • pleadingtrack/Etjet > 0.8 Full t selection efficiency: signal 11-15%, tt->bbt+nln 5%, W+3jets 1% pleadingtrack/Etjet forETt jet> 40 GeV andpleadingtrack > 20 GeV R. Kinnunen Helsinki Institute of Physics

  10. Helicity correlations in full simulation Search for heavy charged Higgs bosons with mH+ > mtop in gg -> tbH±, H± -> tn All hadronic t decays channels included tidentification: • Trigger cuts: ETt jet> 93 GeV (Level-1), pTleading track> 25 GeV(HLT) • Main cuts for the off-line t selection: • ETt jet> 100 GeV • 1 or 3 tracks in a small signal cone of DR = 0.04 • isolation of the signal cone in 0.04<DR<0.4 • pleadingtrack/Etjet > 0.8 R. Kinnunen Helsinki Institute of Physics

  11. Signal and background distributions for pleadingtrack/Etjet t -> 3p± Distributions affected by the trigger selection t-selection efficiencies including pre-selection, trigger and off-line Large suppression of backgrounds with genuine t’s R. Kinnunen Helsinki Institute of Physics

  12. Exploiting helicity correlations in 3-prong t decays The 1-prong t selection with pleadingtrack/Etjet > 0.8 suppresses the 3-prong tdecays from 15% to 3% in the full simulation of the gg -> tbH±, H± -> tnchannel • New idea1) of exploiting more efficiently the 3-prong tdecays • based on the decay mode without any accompanying p0’s: t-> p±p± p± n2/3rd the 3-prong decays (10% of total) This mode can be selected with matching of tracker momentum and calorimeter signals or by a veto on accompanying p0->2g in ECAL • The a1L contribution can be enhanced with a cut in the t momentum • fraction carried by the like-sign pair • R3 < 0.4 or R3 > 0.8, R3 = pp±p±/pt-jet 1) M. Guchait, R. Kinnunen, D.P. Roy, hep-ph/0608324. R. Kinnunen Helsinki Institute of Physics

  13. Exploiting helicity correlations in 3-prong t decays Study for the gb -> tH±, H± -> tn channel l Event generation with PYTHIA, t decays with TAUOLA l Background from tt events l Fast simulation of CMS detector, jet and missing ET reconstruction l No trigger simulation R3 = pp±p±/pt-jetdistributions for t-> 3p± with ETtjet > 100 GeV R. Kinnunen Helsinki Institute of Physics

  14. Exploiting helicity correlations in 3-prong t decays ”Standard” selection used for 1-prong t decays only R. Kinnunen Helsinki Institute of Physics

  15. Exploiting helicity correlations in 3-prong t decays New selection for 3-prong t decays Selection oft->p±p±p±nwithDE = |Etrktot - Ecaltot|<10 GeV ~ calorimeter resolution For R3p < 0.4 the event is triggered at HLT with the 3th opposite sign (hard) pion R. Kinnunen Helsinki Institute of Physics

  16. Discovery potential with 3-prong selection gb -> tH±, H± -> tn 30 fb-1 100 fb-1 Effect of trigger simulation estimated to increase the discovery limits in tanb with 25% R. Kinnunen Helsinki Institute of Physics

  17. Conclusions Opposite t helicity correlations in the H± -> tnand W± -> tn decays allow suppression of the backgrounds with genuine t’s from tt and W+3jet events to a low level with the requirement pleadingtrack/ptjet > 0.8 in the 1-prong tdecays The discovery reach can be enlarged by ~ 18-12% in tanb with a 3-prong selection demanding the like-sign pion pair to carry more than 80% or less than 40% of the t jet momentum R. Kinnunen Helsinki Institute of Physics

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