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CMS
A Compact Solenoidal Detector for LHC
One of the four
pp detectors at
the 14 TeV LHC
Main physics
goal:
Higgs, SUSY
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
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Experimental conditions at LHC
Machine luminosity 1034 cm-2 s-2
inel = 100 mb  109 events/s
higgs = 1 pb
 10-2 events/s
20 events/crossing  1000 tracks
1 crossing/25ns
Neutrons: 2 •1013 n/cm2
Gammas: 5 •103 Gy
in 10 years
Extreme conditions for detectors
•Granularity (105 107 channels)
•Speed of response
•DAQ + trigger (109 102 ev/s)
•High radiation resistance
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
2
CMS ECAL parameters
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
3
CMS ECAL
The choice of PWO
• Fast scintillation
• Small X0, RM
• Intrinsic radiation hardness
• Relatively easy to grow
• Massive production capability
M. Diemoz, E. Longo
• Low light yield
• High refractive index
• LY dependance on T
INFN and La Sapienza University - Roma
4
CMS ECAL
Main problems faced during R&D
•
•
•
•
•
•
Low level of light yield of crystals
Decay kinetics of radiative centers in PWO
Radiation resistance
Light read-out in strong magnetic field
Design of low-Z mechanical structure
Production, test and assembly of  8104 crystals
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
5
unit cell of PbWO4
120
PWO2145
PWO3503
PWO3660
Emission spectra
100
80
Pb2+
60
40
20
0
300
350
400
450
Wavelength (nm)
500
550
600
(WO4)2-
10
pulse
1
400 nm
500 nm
intensity (a.u.)
0.1
0.01
0.001
(WO4)2-regular center
emitting @ 420 nm
0.0001
-5
10
Photoluminescence decay
-6
10
-10
-9
M. Diemoz,
E.10
Longo
10
M. Diemoz - INFN Rome/CMS-ECAL
-8
10
time (s)
-7
10
-6
-5
INFN
University - Roma
10 and La Sapienza
10
WO3 defect center
emitting @ 480-520 nm
6
PWO emitting centers
Slow component induced by
Impurities and defects in
the structure
Few years of R&D to reduce it
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
7
PWO as grown
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
8
PWO as grown ENDCAP size
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
9
Almost final
barrel crystals
98
95
Crystals R&D
100
90
The oretical transmission from Fre snel losses
80
Transmission (%)
70
60
98 crystal
50
95 crystal
40
30
20
10
0
300
M. Diemoz, E. Longo
350
400
INFN and La Sapienza University - Roma
450
500
W avelength (nm)
550
600
650
700
10
[cm]
Facts on crystal’s radiation damage

No damage by neutrons
An effect observed with g
EB
 No damage to scintillation
mechanism
EE
 Only transmission properties
affected through formation
[Gy]
of color centers due to defects
5
-1
Total dose after 10 years of running (5x10 pb )
changes can be tracked through
light injection monitoring system
EB
 Equilibrium (“saturation”) observed
 Recovery observed
EE
 Loss in extracted light of few %
tolerable

Dose rates [Gy/h] in the ECAL luminosity L=1034cm-2 s-1
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
11
g induced radiation damage
creation of hot electrons and holes e/h
e/h separation, thermalization, diffusion
e/h separate localization at suitable lattice sites
defects (e.g. O vacancies)
color centers
s
t
r
a
t
e
g
y
reduce defects
M. Diemoz, E. Longo
absorption
of light!
•Optimize stoechiometry
•Doping
INFN and La Sapienza University - Roma
12
g induced radiation damage
80
0.5
70
0.4
50
m (m-1)
T(%)
60
40
30
initial
20
after irradiation
0.3
0.2
0.1
10
0
0
300
350
400
450
500
550
600
650
700
300
350
wavelength (nm)
400
450
500
550
600
650
700
wavelength (nm)
Radiation damage results in a decrease of transmission Trad () < T0 ()
Is quantified by:
 T0 ( )  -1
1
m ( ) 
ln 
m
L xtl  Trad ( ) 
LYloss = LYrad/LY0
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
13
Combined result
100
95
90
85
g
80
0.15 Gy/h front irradiation
Non optimized raw material Mid 96
Stoechiometry optimization End 96
75
Doping tests April97
Optimized doping & stoechiometry July97
Source TIS
Setup PPE-TA2
70
0
M. Diemoz, E. Longo
M. Diemoz - INFN Rome/CMS-ECAL
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2
3
Dose (Gy)
INFN and La Sapienza University - Roma
4
5
14
Effect of trivalent doping La3+
M. Diemoz, E. Longo
INFN and La Sapienza University - Roma
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