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Inefficiency of Photon Detection

Inefficiency of Photon Detection. May 26, 2005 Takao Inagaki (KEK). Introduction. Three sources of inefficiency Punch-through, sampling and photonuclear effects Estimation is very hard for the photonuclear effect by calculation.

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Inefficiency of Photon Detection

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  1. Inefficiency of Photon Detection May 26, 2005 Takao Inagaki (KEK)

  2. 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.

  3. 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. 1~0.1% mis-tagging exists mainly due to Meller scattering. e + “e”→ e + e

  4. 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, 1980’s.

  5. Equation to estimate the inefficiency in the present experiments Ecal: Energy deposit in the sample calorimeter ηLS: efficiency of neutron detection (overall)

  6. Energy deposit in a sample (CsI)

  7. n/γseparation A.U.N. is essentially a ratio of ADC taken by short and long gates with a correction of time-walk.

  8. 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)(1+μ) for MLS≧2

  9. Photon energy dependence of Poisson μ,averaged multiplicity

  10. Tendency with deposit energyRatio with the electromagnetic shower

  11. Inefficiency for CsI calorimeters 10 MeV threshold CsI-Ⅰ 7×7×30㏄ CsI-Ⅱ 5×5×50㏄ LPS Experiment (2.93±0.89+1.15-0.44)×10^-7 for γ energy 1.5-2.4 GeV

  12. Threshold dependence of inefficiency for CsI-Ⅰ

  13. Inefficiency for sampling calorimeters 10 MeV threshold LPS Experiment (8.3±1.7+13.5-1.2)×10^-7 for γ energy 1.5-2.4 GeV

  14. Threshold dependence of inefficiency for Pb-1mm/S-3mm

  15. 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 PSD+CsI 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 Kπ2 and Kπ3.

  16. Discussion (2/4) • New resultsA very large threshold-dependence is observed in both CsI and sampling calorimeters. Taken into account the fact that the factor of main-background Kπ2 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 πννphysics, 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.

  17. Discussion (3/4) Basic points of this method High multiplicity of evaporation neutrons after a photonuclear interaction

  18. Discussion (4/4) The photonuclear process without excitation of the target nuclei is highly suppressed. σ０/σγN＝3×10＾（-5）/16×0.15 　　　　　　　　　＝1.25×10＾（-5） for O16

  19. Supplement

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