Search for supersymmetric neutral Higgs bosons in the decay channel AHm m in the ATLAS detector

1
Search for supersymmetric neutral Higgs bosons
in the decay channel A/H-gtmm- in the ATLAS
detector

• George Dedes , Sandra Horvat
• Max-Planck-Institut für Physik München
• Deutsche Physikalische Gesellschaft 2005

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Outline

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

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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

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A/H-gtmm decay channel

• Enhanced production rates w.r.t. Standard Model
• For mAgt150 GeV both H,A degenerate in mass
• Clean signature from 2 high pT muons
• Two production mechanisms
• For large tanb (gt10),
• associated production
• is dominant

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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-gtmm rejection

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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
phi (rads)
eta
pT (GeV)
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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
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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 mmmmAdm
Analysis 1
Standard set of Cuts
Event Loop
N(b-jets)gt0 mmmmAdm
Analysis 2

• Standard set of cuts 1. pT gt 20 GeV
• 2. pTmiss lt 20 GeV
• 3. pT2m lt 100 GeV

mA/H 150 , 300 , 450 GeV dm 5 , 10 , 15
GeV
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Discriminating variables
Z
A/H , 150 GeV
pT gt 20 GeV , trigger selection
pTmiss lt 20 GeV
A/H , 300 GeV
tt
A/H , 450 GeV
Z
A/H
Z
tt
A/H
pT2m lt 100 GeV
tt
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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)
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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!

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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 gt 60 GeV

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Signal significance after additional cuts at L
30 fb-1,tanb 30
Invariant mass of A/H - before
Nevents
5s discovery curves at L30 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)
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Summary

• Study of the A/H discovery potential in the A/H
  -gt 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