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George Dedes , Sandra Horvat Max-Planck-Institut f ü r Physik M ü nchen

Search for supersymmetric neutral Higgs bosons in the decay channel A/H-> m + m - in the ATLAS detector. George Dedes , Sandra Horvat Max-Planck-Institut f ü r Physik M ü nchen D eutsche P hysikalische G esellschaft 2005. Outline. The ATLAS detector MSSM Higgs decay to m + m -

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George Dedes , Sandra Horvat Max-Planck-Institut f ü r Physik M ü nchen

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  1. Search for supersymmetric neutral Higgs bosons in the decay channel A/H->m+m-in the ATLAS detector George Dedes , Sandra Horvat Max-Planck-Institut für PhysikMünchen DeutschePhysikalischeGesellschaft 2005

  2. Outline • The ATLAS detector • MSSM Higgs decay to m+ m- • Fast – Full Simulation comparison • Analysis • Improvements • Summary

  3. The ATLAS detector Hadronic Calorimeter S. C. Air core Toroids S. C. Solenoid Inner Detector Electromagnetic Calorimeter Muon Spectrometer • Initial luminosity : 20 fb-1 per year • Nominal luminosity : 100 fb-1 per year • Operating for 1.5 years at initial luminosity : 30 fb-1

  4. A/H->mm decay channel • Enhanced production rates w.r.t. Standard Model • For mA>150 GeV both H,A degenerate in mass • Clean signature from 2 high pT muons • Two production mechanisms : • For large tanb (>10), associated production is dominant

  5. Background • Large background contribution : • (sxBR)B up to 100000x(sxBR)S Strong rejection needed in order to suppress background • b – tagging essential for Z/g*->mm rejection

  6. ATLFAST – Full Simulation comparison • PYTHIA generator program • ATLFAST – A fast simulation program with parametrized description of the detector response • FULL SIMULATION – A detailed description of the detector response, in each measurement unit of the detector b-jet efficiency vs pT b-jet efficiency vs eta b-jet efficiency vs phi Full simulated b-jets / muons efficiency efficiency efficiency Fast simulated b-jets / muons Full simulated fake b-jets / muons Fast simulated fake b-jets / muons pT (GeV) eta phi (rads) muon efficiency vs pT muon efficiency vs eta muon efficiency vs phi efficiency efficiency efficiency pT (GeV) eta phi (rads)

  7. ATLFAST Analysis strategy • Analysis of fast simulated data (ATLFAST,ATHENA version 8.7.0) • First goal: The reproduction and comparison with the most recent study D.Cavalli , P.Bosatelli : ATL-COM-PHYS-99-013 • Data samples produced with ATLFAST 2 times higher statistics for the signal 10 times higher statistics for background

  8. ATLFAST Analysis strategy • ATLFAST parametrization (for 1.5 years at initial luminosity): average muon pT resolution of 3% muon detection efficiency 93% average b-tagging efficiency 60% N(b-jets)=0 mmm=mA±dm Analysis 1 Standard set of Cuts Event Loop N(b-jets)>0 mmm=mA±dm Analysis 2 • Standard set of cuts: 1. pT > 20 GeV 2. pTmiss < 20 GeV 3. pT2m < 100 GeV mA/H = 150 , 300 , 450 GeV dm = ± 5 , ± 10 , ± 15 GeV

  9. Discriminating variables Z A/H , 150 GeV pT > 20 GeV , trigger selection tt A/H , 300 GeV pTmiss< 20 GeV A/H , 450 GeV Z A/H Z tt A/H pT2m< 100 GeV tt

  10. Signal significance at L = 30 fb-1,tanb = 30 • Analysis 1: Lower signal significance, large contribution of the Z-background • Analysis 2: Larger signal significance, Z-background suppressed • Need more statistics for better precision Nevents A/H mass (MeV)

  11. b-jets properties • b – tagging efficiency decreases for low pT and high |h| • b – jets from bbA/H populate a more forward region • b – jets from tt are more energetic Z bb(A/H) tt bb(A/H) tt • possible improvement!

  12. Additional cuts Introducing new selection criteria according to b-jets information : • Require exactly one b-jet (instead of more than 0) in Analysis 2 • Rejecting events with PTbjet > 60 GeV

  13. Signal significance after additional cuts at L = 30 fb-1,tanb = 30 Invariant mass of A/H - before Nevents 5s discovery curves at L=30 fb-1 before – after additional cuts tanb previous analysis After additional cuts A/H mass (MeV) Invariant mass of A/H - after Nevents mA(GeV) A/H mass (MeV)

  14. Summary • Study of the A/H discovery potential in the A/H -> m+ m- decay channel , using ATLFAST data • Good agreement between ATLFAST and Full Simulation • Obtained results agree with those from the previous analysis • Larger statistics in both signal and background needed for a better precision on the signal significance • Higher rejection of the tt background achieved by using b-jet properties • Next step: analysis refinements , using further information from b-jets …

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