Inefficiency of Photon Detection

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Inefficiency of Photon Detection

• May 26, 2005
• Takao Inagaki (KEK)

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Introduction

• Three sources of inefficiency
• Punch-through, sampling and photonuclear
  effects
• Estimation is very hard for the photonuclear
  effect by calculation.
• A series of experiments, ES147 and ES171 have
  been performed to measure it.

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Set-up of ES147 and ES171

• Electron beam from INS 1.3-GeV ES
• Photon tagging system, 32 8 (backing) counters,
  detects recoil electrons after bremsstrahlung.)
• Samples were placed behind a shield through
  active collimation.
• Still not so perfect photon-tagging to make a
  direct measurement of inefficiency. 10.1
  mis-tagging exists mainly due to Meller
  scattering.
• e e? e e

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Additional tagging for photonuclear process

• 12 modules of liquid scintillator, which can
  identify neutron, surround the sample.
• A similar method was used for the measurement of
  total photonuclear cross section in Saclay,
  1980s.

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Equation to estimate the inefficiency in the
present experiments
Ecal Energy deposit in the sample
calorimeter ?LS efficiency of neutron detection
(overall)
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Energy deposit in a sample (CsI)
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n/?separation
A.U.N. is essentially a ratio of ADC taken by
short and long gates with a correction of
time-walk.
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Estimation of overall neutron detection efficiency

• By fitting the hit multiplicity distribution with
  a Poisson distribution
• Eff 1-exp(-µ)
• for MLS?1,
• Eff 1-exp(-µ)(1µ)
• for MLS?2

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Photon energy dependence of Poisson µ,averaged
multiplicity
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Tendency with deposit energyRatio with the
electromagnetic shower
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Inefficiency for CsI calorimeters
10 MeV threshold CsI-? 7730? CsI-?
5550? LPS Experiment (2.930.891.15-0.44)10-
7 for ? energy 1.5-2.4 GeV
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Threshold dependence of inefficiency for CsI-?
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Inefficiency for sampling calorimeters
10 MeV threshold LPS Experiment (8.31.713.5-1.
2)10-7 for ? energy 1.5-2.4 GeV
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Threshold dependence of inefficiency for
Pb-1mm/S-3mm
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Discussion (1/4)

• Excuse! Long time many students analyzed data
  in different ways and they left. It was very hard
  to reanalyze in a common criteria.
• Reproduction ES-147 values are nicely reproduced
  by ES-171 for CsI and the inefficiency is not
  significantly different between modules of
  different size. LPS data at higher energy looks
  consistent with ES-171 and ES-147 (CsI).
• The sampling calorimeter data of ES-147 look
  inconsistent with those of ES-171. It is
  difficult to check the ES-147 data, now. We
  guess, it is due to a difference of neutron ID.
  The ID in ES-147 was only PSD for the sampling
  calorimeter and PSDCsI timing for CsI. ES-171
  used TOF and A.U.N (ratio of ADC with different
  gate width), which might be tighter than the ID
  for the ES-147 sampling calorimeter.
• We have not yet seriously tried an
  inefficiency estimation using real data of E391a,
  such as Kp2 and Kp3.

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Discussion (2/4)

• New results A very large threshold-dependence is
  observed in both CsI and sampling calorimeters.
  Taken into account the fact that the factor of
  main-background Kp2 remaining is square of the
  single-photon detection inefficiency, setting a
  lower detection-threshold is crucial.
• A systematical change is suggested in the
  inefficiencies for three different samplings. It
  correlates with the ratio of nuclear interaction
  length with radiation length and looks natural by
  considering that inefficiency arises through a
  competition between photonuclear and
  electromagnetic interactions.
• Next step Any experimental efforts of
  inefficiency measurement will be appreciated.
  Cross checks are specially required for the
  ES-147 result and the systematic behavior for
  different sampling.
• There is a clear limit in this method.
  Neutron multiplicity decreases with energy. The
  inefficiency below 150 MeV, which is still very
  important for p?? physics, should be examined
  with a different method like E949.
• We heard that a recent development of
  simulation for the LHC experiments is remarkable.
  It might be a time to start a cooperative work
  for the inefficiency study among K phycisists.

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Discussion (3/4)

• Basic points of this method
• High multiplicity of evaporation neutrons
• after a photonuclear interaction

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Discussion (4/4)

• The photonuclear process without excitation
• of the target nuclei is highly suppressed.

s0/s?N310(-5)/160.15 1.2510(-5)
for O16
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Supplement
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