G. Atoian, S. Dhawan, V. Issakov, A. Poblaguev, M. Zeller,

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G. Atoian, S. Dhawan, V. Issakov, A. Poblaguev,
M. Zeller, Physics Department, Yale University,
New Haven, CT 06511 G.I. Britvich, S.
Chernichenko, I. Shein and A. Soldatov Institute
for High Energy Physics, Protvino, Russia
142284 O. Karavichev, T. Karavicheva and V.
Marin Institute for Nuclear Research of Russian
Academy of Sciences, Moscow, Russia 117312
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• The requirements to the KOPIO Photon Calorimeter
• Energy resolution ? 3.5/?E.
• Time resolution ? 100psec/?E.
• Photon detection inefficiency (due to
  holes-cracks) ? 10-4.
• Granularity ?11?11 cm2.
• Active area ? 5.3? 5.3 m2
• Radiation length ?16X0
• (18X0 including Preradiator).
• Physical length ? 60 cm.
• The Shashlyk technique satisfies the KOPIO
  requirements.

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The main directions for improving of the energy
resolution up to 3/?E(GeV) are (i) sampling,
(ii) photo-statistics, and (iii) light collection
uniformity.
New mechanical design (sampling) A very fine
sampling structure of Shashlyk module - 300
alternating layers of 275 ?m thick lead tiles and
1.5 mm thick scintillator tiles with LEGO type
locks. These locks fix the position of the
scintillator tiles with the 350 ?m gaps,
providing a sufficient room for the lead tiles
without optical contact between lead and
scintillator. The new mechanical structure
involves removing 600 paper tiles between
scintillator and lead, reducing the diameter of
the fibers hole to 1.3 mm and removing the
compressing steel tape at the side of the module.
Compared to previous designs, the sampling ratio
was improved by factor of 1.25, the hole/crack
and other insensitive areas were reduced from 2.5
up to 1.6 , the effective radiation length X0
was reduced from 4.0 cm to 3.5 cm and the module
mechanical properties such as dimensional
tolerances and constructive stiffness were
significantly improved.
New scintillator tile (light yield,
uniformity) Molding scintillator
(BASF143E1.5pTP0.04POPOP produced by IHEP)
with improved optical transparency and improved
surface quality. The light yield is 60 photons
per 1 MeV of incident photon energy.
Nonuniformity of light response across the
module is lt2.3 for a point-like light source,
and lt 0.5 if averaged over the photon shower.
New photodetector (photo-statistics) A 16 mm
diameter Avalanche Photo Diode (630-70-74-510
produced by Advanced Photonix Inc.) with high
quantum efficiency (93), high gain (200), low
excess noise factor (2.4), good photo-cathode
uniformity (nonuniformity ? 3) and good short-
and long-term stability. The effective light
yield of a module became 55 photoelectrons per 1
MeV of the incident photon energy resulting in
negligible photo statistic contribution to the
energy resolution of the calorimeter.
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Scintillator PSFluor1Fluor2, Manufacturer Light yield ( of Anthracene) Attenuation Length (cm) Light yield of MIP, p.e. per tile Simulated light collection efficiency
PSM1151.5pTP0.04POPOP, TECHNOPLAST, 1998 53 ? 6 4.0 ? 0.4 4.4 ? 0.3, 100 0.134 ? 0.013, 100
BASF158K1.5pTP0.04POPOP, IHEP, 2001 56 ? 6 5.1 ? 0.6 5.6 ? 0.3, (127 ? 10) 0.170 ? 0.017, (127 ? 13)
BASF165H1.5pTP0.04POPOP, IHEP, 2001 56 ? 6 6.1 ? 0.6 6.4 ? 0.3 (145 ? 10) 0.191 ? 0.019, (143 ? 14)
BASF143E1.5pTP0.04POPOP, IHEP, 2002 54 ? 6 6.8 ? 0.5 7.1 ? 0.3, (161 ? 10) 0.215 ? 0.021, (160 ? 16)
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Lateral segmentation 110?110 mm2
Scintillator thickness 1.5 mm
Gap between scintillator tiles 0.350 mm
Lead absorber thickness 0.275 mm
Number of the absorber layers (Lead/Scint) 300
WLS fibers per module 72 ? 1.5 108 m
Fiber spacing 9.3 mm
Holes diameter in Scintillator/Lead 1.3 mm/1.4 mm
Diameter of WLS fiber (Y11-200MS) 1.0 mm
Fiber bundle diameter 14.0 mm
External wrapping (TYVEK paper) 150 ?
Effective Xo 34.9 mm
Effective RM 59.8 mm
Effective density 2.75 g/cm3
Active depth 555 mm (15.9 Xo)
Total depth (without Photodetector) 650 mm
Total weight 18.0 kG
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• Studied prototypes
• 1st prototype of 3?3 modules
• The conventional design of modules (with paper
  between lead and scintillator)
• A 30 mm diameter 9903B PMT (Electron Tube
  Inc.)
• The conventional 12-bits ADC digitizing of the
  PMT signal.
• 2nd prototype of 3?3 modules
• New design of modules (no paper between lead and
  scintillator)
• A 16 mm diameter 630-70-74-510 APD (Advanced
  Photonix Inc.)
• An 8-bits 140 MHz WFD and 12-bits ADC digitizing
  of the APD signal.
• Measurements
• Beam intensity was 3?105 Hz.
• Triggered and tagged photon energy was in the
  range 220 - 370 MeV.
• Beam angle spread was 2 mrad.
• Diameter of the beam spot at the prototype was
  1.5 cm.
• Photon energy spread was ?E/E ?1.5 (for the
  triggered and tagged monochromatic photon energy
  line).

Two KOPIO calorimeter prototypes were tested at
the Laser Electron Gamma Source (LEGS) facility
at BNL NSLS.

• The energy resolution was measured for both
  prototypes with the beam in the center of nonet.
• The time resolution was studied for the 2nd
  prototype (with WFD only), comparing timing in
  two modules when the beam is between the two.
• The photon detection inefficiency was measured
  by the detecting photons in Prototype 1 located
  behind Prototype 2.

• The stability of the Calorimeter signals was
  tested by a LED monitoring system during the
  24-hours measurements

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The best results were achieved for prototype 2
with APD/WFD readout
Energy resolution ? (2.90.1)??E(GeV).
Time resolution ? (9010)psec ??E(GeV).
Photon detection inefficiency ? 5?10-5 (for incident beam angle ? 5 mrad ).
APD gain stability ? 1 (for tested period of 24 hours).
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The simulation of the Shashlyk calorimeter in
KOPIO is based on a GEANT3 description of the
development of the electromagnetic shower, and an
Optical Model for the simulation of the light
collection in the scintillator tile. The GEANT3
part of the simulation includes a detailed
description of the geometry of the Shashlyk
module. Calculations are performed with low
energy cuts 10 KeV and with delta-ray simulations
to obtain consistency with experimental results.
The Optical Model uses the tracking of the single
photons in the scintillator tile. The parameters
which customize the model, such as attenuation
lengths, reflection efficiencies, the probability
of photon capture in the fiber, were adjusted
using optical measurements. The effects of light
to photoelectron conversion and noise in the
photodetector-preamplifier chain were also taken
into account. The results of the simulation of
the energy resolution are in excellent agreement
with the experimental measurements in a range of
photon and positron energies 0.25 - 2.0 GeV.
Experiment vs GEANT/OPTIC simulation
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Development of Calorimeter (2004)

Development of the photodetector HV system

Basic unit of the photodetector HV system will be
a new commercial LV-HV converter with analog
control (C20 produced by EMCO HIGH VOLTAGE
CORPORATION ). This HV supply provides very low
ripple, high stability and low pick-up
noise. Analog control of C20 will be done by a
commercial 12-bits D/A converter (64-channels
IP/VME module - XIP-TVME200/XIP-5220, produced by
Xycom Automation Inc.). Expected cost of HV
system per channel is 140.
A sample of the APD HV "built-in" unit with a
new LV-HV converter was tested. The 25-channel
prototype of this HV system will be build and
tested with the new Calorimeter prototype.
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Development of Calorimeter (2004)
Development of the photodetector cooling
system
A tested APD cooling system
Room temperature (21 ? 28) oC
APD temperature 18 oC
Improvement of a signal/noise ratio (1.3 ? 1.5)
Equivalent Noise 0.5 MeV
APD gain stability ? 1
An improved prototype of the cooling
system will provide the APD noise of 0.2 ? 0.3
MeV (at 10 oC).
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Development of Calorimeter (2004)
Development of the LED monitoring system
Temperature stability ? 0.1
Duration of the light pulse ? 20 nsec
Variation of the flash amplitude ? 0.1
Photon intensity ? 10,000 p./ch.
Pulse rate Up to 1 MHz
A 64-channel LED monitoring system will
be built and tested with the new Calorimeter
prototype.
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Development of Calorimeter (2004)
Development of the photo-readout system,
including the digitizing readout electronics

• Study of 25 APDs (final specification and cost).
• Study of 25 commercial fast charge-sensitive or
  voltage pre-amplifiers (final specification and
  cost).
• Study of new WFD prototypes (10-bit, 250 MHz).

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Development of Calorimeter (2004)
Development of Calorimeter conception
design
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Development of Calorimeter (2005)

• Development of the conceptual and technical
  design of the Calorimeter system
• The main questions are
• What is the beam hole size?
• What is design of beam pipe inside Calorimeter
  hole?
• Could we shift Sweeping magnet downstream, to
  create a service zone for Calorimeter?

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Beam test of Calorimeter (2004)
Summer-Fall 2004 Construction and test of
5?5 pre-production modules array with the final
version of modules instrumentation. This
prototype will be employed to test the
performance of the pre-production modules and to
adjust the specification for the digitizing
system and other accompanying systems.
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Beam test of Calorimeter (2005)
Fall 2005 Construction and test of 10?10
mass-production modules array with appropriate
pre-production prototypes of the digitizing,
cooling and monitoring systems. In
collaboration with those responsible for the
Preradiator, this prototype will be employed to
study the energy and timing performance of a
joined Calorimeter/Preradiator system.
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• References
• KOPIO collaboration, Measurement of the decay
  K0 ? ? ???, Technical Design Report for the
  National Science foundation, June 06, 2001, page
  53.
• G. S. Atoian et al,, Preliminary Research for
  Shashlyk Calorimeter for E926 , KOPIO TN015, 15
  June 1999, physics/0310047. .
• G.S. Atoian et al., Study of the energy
  resolution of the KOPIO Preradiator/Calorimeter
  system , KOPIO TN034, 18 Apr 2002.