BNL-E787/E949実験で用いた
エンドキャップ純CsIガンマ線検出器
村松憲仁 東北大学電子光理学研究センター
ELPH研究会 「素粒子・原子核実験における全吸収型
カロリメータの実例と応用」 2015年3月10日
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興味のある方は
I-H. Chiang et al., IEEE Trans. Nucl. Sci., Vol. 42 (1995) 394.
T.K. Komatsubara et al., Nucl. Instr. Meth. A 404 (1998) 315.
を参照してください。
BNL-E787/E949 Experiment
K : One of the Golden
Modes for study of the CKM matrix
and CP violation.
K   μ ν
Muon Band
K   μ  νγ
Signal region
BR(K+)  |Vtd|2
BR[SM] = (8.01.0) 
Range
Tail
K   π  π0
1011
Beam background
2
BNL-E787/E949 History
1988-1989 E787 Phase-I
1992 Japan-US (Phase-II) start
endcap photon detector
Pb+Sci. w/ long light guide

undoped CsI w/ fine-mesh PMT
1995-1998 data taking
1999 E949 approved by DOE
beam intensity upgrade
new barrel photon veto
2001-2002 data taking
cancellation by DOE
2005 RSVP cancellation by NSF
Most of detector & DAQ system
has been transferred to SPring-8.
Number of stopped K+
3
K++ Result (above the K++0 peak)
10
BR( K     )  1.4710..30

10
(68%CL interval)
89
▲ : E949 data
○ : E787 data
Solid line : E949 signal region
Dashed line: E787 signal region
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Tokiyasu
This afternoon
E787/E949 Detectors
1 Tesla
B-field
Endcap
CsI Det.
710 MeV/c K+ Beam (K/ ratio = 3:1)
Incoming : 6 MHz, Stopping :  2 MHz
Endcap CsI Detector
High efficient -veto in 0225 MeV range.
Lower accidental veto rate near the beam.
(old EC: a.v.r.30% @ 0.3 MHz stopped K+)
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Endcap Undoped CsI Detector
25 cm (13.5X0)
Produced by
Crismatec.
Total 143 crystals
(upstream : 75,
downstream: 68)
Dry N2 gas flow to
keep temperature
(41.7 C) and
humidity (515%).
Gain monitor by
a light pulser.
6
Fine-Mesh PMT
☺ Work at 1 Tesla magnetic field. (Gain drop @ 1 Tesla : 2107  5105)
180300 p.e./MeV (w/ PMT QE of 16%)  old EC : 10 p.e./MeV
Short transit time & small time jitter.
☻ Only 40% of single photoelectron hit the 1st dynode.  Gain variation
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Undoped CsI Decay Time Constant
• We observed Fast component :   30 nsec,   300 nm
& Slow component :   680 nsec,   450 nm.
• The ratio of fast component  0.8
• UV-transmitting optical filter (U330 by Kenko Co.)
from Saint-Gobain Data Sheet
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Crystal-by-crystal Variation
Pulse height (arbitrary unit)
BNL CsI crystals
6888%
Time [nsec]
FOREST pure CsI [very rough analysis]
=44.4 ns (0.732) + =240.9 ns (0.268)
General comments from Prof. Kobayashi
The slow component is produced by the radiative recombination of excited
electrons, which are captured at lattice defects. The metal impurity at the
magnitude of ppm order will affect the crystal growth & quality.
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Signal Read-out
In addition to the Trigger, TDC, & ADC lines, the signal pulse
shapes were recorded for 250 nsec by 500 MHz TransientDigitizers, which were produced based on GaAs CCD at TRIUMF.
(More details in D. Bryman et al., IEEE Trans. Nucl. Sci., vol. NS-38 (1991) 295.)
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Pulse Shape Analysis
• Detection timing is decided by the leading edge at the
constant fraction (0.4).
• 2nd pulses on the 1st pulse tail can be separated above 30 ns.
 Overall photon veto inefficiency 103 (106 for 0)
1st pulse: 10 MeV
2nd pulse: 5 MeV
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Time Resolution
• Timing calibration was done by using K++0 decays.
• The reference timing is obtained from + at the Range Stack.
• 0.7 nsec is achieved at higher energies.
 accidental veto rate  20%
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Photon Energy Measurement
K++0
• Energy calibration was done by
using K++ decays, where
the kinetic energy of + is
monochromatic at 152 MeV.
• 0 energy from K++0 decays :
peaked at 245.6 MeV with
=10.6% (EC-BV combination).
Note =11.8% for BV-BV.
 Rough Energy Resolution :
(EC)=12%, (BV)= 15% at the
average energy of 110 MeV.
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Summary
• E787/E949 Endcap undoped CsI  Detector was introduced for
the sufficient photon veto ability inside the 1 Tesla B-field.
• Its design is optimized to obtain the timing information with
low inefficiency (undoped CsI with the direct connection of
fine-mesh PMT, UV-transmitting optical filter, pulse shape
analysis) and low accidental veto rate (better time resolution,
pulse shape analysis).
• These techniques may be usable for the photon detectors
under the high rate environment.
• Because of the special purpose, this  detector was not
optimized for calorimetry. (1 Tesla B-field, fine-mesh PMT)
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Active Photon Detection for the studies
of chiral perturbation theory
K++0, K++, K++0
Photon energies are measured by Barrel Photon Detector,
& the other activities are vetoed at Endcap.
Talk about the Barrel Photon Detector : Tokiyasu this afternoon.
IB (Internal Bremsstrahlung)
DE (Direct Emission)
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Latest developments in PMTs for low temperature operation

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