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Longitudinal transmission
20
35
Mean value: 17.188%
Standard dev. : 2.63%
15
T @ 350 nm
Number of cryst al s
Number of cryst al s
40
30
20
Mean Value : 61.47%
Standard dev. : 4.85%
30
Mean Value : 70.5%
Standard dev. : 3.3%
T @ 420 nm
25
T @ 620 nm
Number of cryst al s
50
10
5
10
0
20
15
10
5
0
5
10
15
20
25
Transmission at 350nm (%)
30
0
35
30
35
40
45
50
55
60
65
Transmission at 420nm (%)
70
75
80
0
30
35
40
45
50
55
60
65
Transmission at 620nm (%)
70
75
80
100
Transmission (%)
absorption @ 350 nm
and band-edge slope:
radiation hardness
90
Theoretical transmission from Fresnel losses
absorption @ 620 nm:
core defects
(e.g. bubbles)
80
70
60
98 crystal
50
95 crystal
40
30
20
absorption @ 420 nm:
small Labs at emission peak10
0
300
M. Diemoz, E. Longo
350
400
450
500
550
Wavelength (nm)
INFN and La Sapienza University - Roma
600
650
700
1
Light collection and non uniformity
Npe/ MeV
all polis hed
Ra = 0.34
Ra = 0.24
16 .5
16
15 .5
• High refractive index make light
collection difficult
• Focusing effect due to tapered
shape of crystals
• Treatement of lateral faces
• coating, polishing, diffusing and
reflecting wrapping
M. Diemoz, E. Longo
15
14 .5
14
13 .5
13
12 .5
0
2.5
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5
7.5
10
12 .5 15
17 .5
20
22 .5
25
Dist. from PMT (cm)
2
Effect of longitudinal non uniformity
• Optimal non uniformity of light collection to
maintain contibution to the constant term in
the energy resolution below 0.3%
Optimal
RNUF
Region of shower max
FNUF
Any slope can
be accepted
mm
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
3
Control of longitudinal non uniformity
Front d(LY)/dX0=0.35%/X0
• uniformity controlled
by depolishing one
lateral face with a
given roughness
20
g
FNUF
LY
Mean value : 0.05 %/Xo
s: 0.24 %/Xo
Batch 2
15
10
5
• pay a loss in LY
0
-2 -1.8-1.6-1.4-1.2 -1 -0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Non Uniformity - Front (%/Xo)
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INFN and La Sapienza University - Roma
±0.35 %/Xo
4
Effect of longitudinal non uniformity
• Resolution @ 120 GeV
(constant term)
measured on test beam
as a function of FNUF
determined in LAB
measurements
• Chinese crystals were
not uniformized
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
5
Crystal quality insurance
Automatic Crystals Quality Control
Systems
for reception tests
•Automatic processing of crystals in
sets of 5 on a tray, also used for
storage and capsule gluing
ACCOCE
at CERN
•Measurements of dimensions by a
standard 3D machine
•Light yield on several points (unif.)
•Transmission (lateral on several
points, longitudinal)
•Bar code ID of each crystal
ACCOR at
information into database, via a
distributed process control system INFN-ENEA
Rome
+ spot checks of radiation tolerance
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6
Photon detector for PWO in CMS
• Not sensitive to 4T magnetic field
• High quantum efficiency for l 400 – 500 nm
• Internal amplification (low PWO LY)
• Fast and good for hogh rate (40MHz)
• Radiation hard
• Not (too much) sensitive to charged particles
Photomultipliers
PIN photodiodes
• affected by magnetic field
• no internal amplification
• large volume
• too sensitive to charged particles
(Nuclear Counter Effect)
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INFN and La Sapienza University - Roma
7
Avalanche Photo Diodes
APD
PIN
6m
200m
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INFN and La Sapienza University - Roma
8
Avalanche Photo Diodes
Barrel: Avalanche Photodiodes (APD, Hamamatsu)
Characteristics optimized with an extensive R&D Program
•insensitive to B-field as PIN diodes
•Internal gain (M=50 used)
•good match to Lead Tungstate scintillation spectrum
(Q.E. ~ 80%)
•dM/dV = 3.5%/V and dM/dT = -2.3%/oC :
T and V stabilization needed
 changes to be tracked through light injection system
•bulk current increase & recovery with irradiation
measured over 1 year: expect doubling of initial noise
after 10 years running, OK
•Capacitance 75 pF
•Excess noise factor F=2.2 ( fluctuations in
multiplication)
•Effective deff  6 m ( response to ionizing radiation)
2 APDs per crystal:
50 mm2 active area
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INFN and La Sapienza University - Roma
9
Avalanche Photo Diodes
Critical points
• Contributions to all terms of energy resolution
• C & Id
 b (1/E)
• excess noise factor 
a (1/E)
• Gain stability
 c
• Nuclear counter effect
• Radiation hardness
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INFN and La Sapienza University - Roma
10
Avalanche Photo Diodes
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INFN and La Sapienza University - Roma
11
APD radiation resistence
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INFN and La Sapienza University - Roma
12
ECAL readout chain
On-detector Light-to-Light readout
• 40 MHz clock
• High dynamic range to measure
an energy interval 50MeV 2TeV
Upper-Level
Readout Card
ALL RADIATION HARD
Current Voltage


Voltage Bits
Energy

Light
Light

Current
Current

Voltage
Pipeline
Bits

Light
Voltage

Bits
To DAQ
Bits

Light
S
Digital
Trigger S
ADC
PbWO4
Crystal
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APD
VPT
Floating-Point
Preamplifier
ADC
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Fiber
Readout
13
ECAL calibration and monitoring system
•Precalibration in the test beam of some supermodule, two energies
•Monitoring of evolution by light injection system
•In situ calibration with physics events ( Z  e+e- ) using E/p from tracker allows at low
luminosity achieve in 35 days intercalibration better than 0.3%.
DATA LINK
DATA LINK
ADC & OPTO
CTRL
FPPA
•1/140 (80 Hz) beam gaps
ADC ( x 12)
CRYSTAL
(1700/SM)
on 850 crystals, ECAL
barrel in 15 min.
MEM
PN
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•light injection
•l = 440 nm and 500 nm
SERIALIZER
APD
(200 Channels)
LASER monitoring
OPTO
LEVEL-1
FANOUT
FE
LEVEL-2
FANOUT
SWITCH
(select SM/2)
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LASER
14
Electron versus light signal
Recovery of damage in
absence of beam
NB moderately rad hard crystals
most suitable for monitoring studies
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INFN and La Sapienza University - Roma
15
Test beam results
280 GeV electrons:
• no sign of rear leakage,
which could cause direct
signal in APD
Resolution as a function of
energy:
• on 1999 prototype, matrix
with 30 preproduction
crystals and APDs
s 2.74%
142MeV

 0.40% 

E
E
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INFN and La Sapienza University - Roma
16
Assembly and test in Rome and CERN
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INFN and La Sapienza University - Roma
17