GEANT Background Studies of the GlueX Cerenkov Detector

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GEANT Background Studies of theGlueX Cerenkov
Detector

• Ryan Mitchell
• UT Visit
• June 8, 2004

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Background Rates

• GlueX expects on the order of 108 photon
  interactions per second.
• Estimates of tagged physics events are around
• 740 events per second (TDR pg. 208).
• How often will physics events be contaminated by
  background in the Cerenkov detector?
• e.g., a kaon can be misidentified as a pion if
  there is a background electron in the Cerenkov
  detector.

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GEANT Details

• Start with a coherent bremsstrahlung beam
  generated by 12 GeV electrons in a crystal
  radiator.
• Simulate the collimators, etc.
• Photon-Hadron interactions are simulated using
  the GelHad package, which takes into account
  nuclear absorption and pion production.
• Electromagnetic cutoffs are 100KeV.
• Hadronic cutoffs are 10MeV.
• Record particle information at the boundary of
  the Cerenkov volume. No Cerenkov radiation is
  simulated.

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Sample Events
Results from 1000 random events. Red e/e-.
Blue photons.
Target
Cerenkov detector
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Sample Events (cont.)
Another 1000 events.
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Particle Types at Cerenkov Volume
Electron background is about 200 kHz.
Photons
Assuming the electrons are evenly distributed in
time, there is a 200,000 x 10x10-9
0.2 chance for a 10 ns window to contain a
background electron.
Positrons
Electrons
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Particle Types (cont.)
Neutron
Other backgrounds are relatively insignificant.
?
?-
Proton
?-
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Background Particles per Event
Average is around 6 (given there is at least 1).
The 0.2 confusion rate is an overestimate since
background particles arrive together.
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Photon Background Origin
Inner ring of Cerenkov
Bcal.
Ecal.
Target
Collimator
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Electron Background Origin
Backgrounds are from the target and the
inside ring of the Cerenkov detector.
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Positron Background Origin
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Background Energies
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Summary

• The first estimate of the accidental rate due to
  background gives a fraction of a percent within a
  10ns time window.
• This can serve as a rough upper limit.
• Electrons were assumed to be equally dispersed in
  time.
• Many electrons will radiate away from the mirrors
  in the current design.
• The GlueX Cerenkov environment appears to be
  clean enough for a rather simple design.