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 Physik München Deutsche Physikalische Gesellschaft 2005

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

Electromagnetic Calorimeter 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

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

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

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)

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 Data N events A→m+m- 20.000 bbA→m+m- Z/g*→m+m- 1.000.000 Z(→m+m-)+jet tt→(mnb) (mnb) 2 times higher statistics for the signal 10 times higher statistics for background

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

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

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 Analysis 1 mA = 150 GeV mA = 300 GeV mA = 450 GeV NS 1196 59 3.8 NB 29828 2137 337 NS / √NB 6.924 1.28 0.21 error ±0.006 ±0.02 Nevents Analysis 2 mA = 150 GeV mA = 300 GeV mA = 450 GeV NS 479 37 2.9 NB 624 47 8.8 NS / √NB 19.2 5.4 0.97 error ±0.8 ±2.9 ±2.80 A/H mass (MeV)

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!

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 Analysis 2 mA = 150 GeV mA = 300 GeV mA = 450 GeV NS 380 27 2.0 NB 310 11 1.9 (NS / √NB) before 19.2 5.4 0.97 (NS / √NB) after 21.6 8.3 1.49

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)

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 …