The Vacuum Phototriodes for the CMS Electromagnetic Calorimeter P R Hobson, D C Imrie, O Sharif
The CMS Electromagnetic Calorimeter
description
Transcript of The CMS Electromagnetic Calorimeter
The CMS Electromagnetic Calorimeter
Roger Rusack
The University of Minnesota
On behalf of the CMS ECAL collaboration
ICHEP Beijing 2004 – R. Rusack
Detector Overview
MUON BARREL
CALORIMETERS
Silicon MicrostripsPixels
ECAL Scintillating PbWO4 crystals
Cathode Strip Chambers ( )CSCResistive Plate Chambers ( )RPC
Drift Tube Chambers ( ) DT
Resistive Plate Chambers ( )RPC
SUPERCONDUCTINGCOIL
IRON YOKE
TRACKER
MUONENDCAPS
HCAL
Plastic scintillator/brasssandwich
ICHEP Beijing 2004 – R. Rusack
Goals
High Resolution calorimetry:
– Stochastic term 2.7%, Constant term 0.5%, Noise term 150 – 220 MeV. Large volume:
– 75,848 crystals covering || < 2.6.
– 90.8 tons of crystals or 10.9 m3. Operated inside a 4T magnetic field. In a radiation environment with an integrated dose of:
– 1013 neutrons/cm2 and 1 kGy at = 0 to 2×1014 neutrons/cm2 and 50 kGy for 2.6.
40 MHz bunch crossing rate.
ICHEP Beijing 2004 – R. Rusack
Lead Tungstate Crystals
Operate at 18o C – Temp dependence = -2.2%/OC.
•Radiation length – 0.83 cm•Molière radius – 2.2 cm.•Fast light output – 80% in 25 nsec.•Relative Light Yield – 1.3% NaI
No long-lived radiation damage.
But short-lived metastable color centers created by radiation – careful monitoring
Transmission
Emission
350 nm
ICHEP Beijing 2004 – R. Rusack
Construction Overview
10 crystals
Submodule
Dee
138 Supercrystals
36 Supermodules
4 Dees
Module
Barrel61,200 PbWO4
crystalsReadout with 122,400 APD’s
Endcap14684 crystals
readout with VPT’s.
ICHEP Beijing 2004 – R. Rusack
PreshowerTwo-layer silicon preshower detector placed in front of the endcap calorimeters
2 Xo absorber 1 Xo absorber
2mm silicon strips to separate ’s from ’s and for vertex identification.
ICHEP Beijing 2004 – R. Rusack
Crystals and crystal production.
Transmission at 420nm Light Yield
All crystals are tested for:• Radiation Hardness,• Light Yield,• Physical Dimensions.• Light yield uniformity.
Projection is 3o off interaction point - 34 different crystal types.
Barrel Crystals are tapered – variation of reponse with origin of the shower.
Correct by roughening one surface of the crystal.
ICHEP Beijing 2004 – R. Rusack
Photodetection4T B-field precludes use of PMT’s..
Avalanche photodiodes in barrel.
Vacuum Phototriodes in Endcap
Two 5× 5 mm2 APD’s/crystal.Gain – 50.QE – 80% @ 420 nm.Temp sensitivity – -2.4%/ OC.
Gain – 10.QE – 15% @ 420 nm.Rad tolerance - <10% at 20 kGy.Operates in high B – field.
ICHEP Beijing 2004 – R. Rusack
Readout Overview• Each crystal has a low-noise, large dynamic range pre-amplifier with three gain outputs each coupled to a separate 40 MHz ADC, to cover the full 50 MeV to 1 TeV range.
• Level 1 trigger sums are sent every bunch crossing.
• Data from each crossing is stored until level 1 trigger accept.
•All data are sent on fiber optic links.
Supercrystal
Front-end board
Data
Trigger sums
Very Front End board
GOH
APD MGPA 3 ADC’s
ICHEP Beijing 2004 – R. Rusack
Front-End Electronics
Barrel – Grouped into a 5 × 5 crystal array.Endcap – Grouped to match
Crystal APD
Amplifier*1
Amplifier*6
Amplifier*12
ADCChannel2 (12bit)
ADCChannel1 (12 bit)
ADCChannel0 (12 bit)
14 bitChannel
Data
Single channel architecture
FE Board
25Trigger Link
Data Link
Creation of trigger primitives.Storage of data to level 1 accept.
Signal from APD’s
~100 W per trigger tower.Total power on detector ~ 50kA, 300 kW.
All front-end electronics in 0.25process.
ICHEP Beijing 2004 – R. Rusack
Optical Data Links
All data is sent off detector electronics via 1 GHz Optical links.
12Rx moduleRx module
12
1GOHGOH1212
1
96
DistributeDistributed Patch d Patch PanelPanel
Back-end Back-end Patch Patch PanelPanel
Off DetectorOff DetectorFront EndFront End Pigtail Pigtail
fiberfiber
RuggedizeRuggedized ribbond ribbon
Dense Dense multi-multi-ribbon ribbon cablecable
GOLGOL Laser Laser diodediode In-Line In-Line
Patch Patch PanelPanel
CMCMSS
PIN photo-PIN photo-diode diode arrayarray
Digital Digital amp. amp. ASICASIC
1212
10,500 links for whole calorimeter – Data flow: 10 Tb/sec.
Radiation hardOff detector
ICHEP Beijing 2004 – R. Rusack
Cooling
All 0.25 electronics runs at 2.5V.
0.45 A/channel1 A/board
Radiation hard regulator has a drop out voltage of 1.5V
Total power in whole calorimeter ~300 kW
Crystal light yield decreases by 2.2%/oC & APD gain decreases by 2.3%/OC.
Removing all excess heat is critical for the stable operation of the detector.
ICHEP Beijing 2004 – R. Rusack
Cooling
Trigger tower on the cooling bars
0.04°C
2 months
Approach: isolate crystals and APD’s from electronics.Remove heat from electronics by close coupling with water cooled bars.
Crystals and APD’s kept to 0.05oC & uniform to 0.2oC.
Temperature stability with a 100-channel system last year.
ICHEP Beijing 2004 – R. Rusack
Test beam : precalibrationWe cannot test calibrate every crystal with an electron beam.
Obtain a first calibration point from component data: crystal light yield, APD & pre-amplifer gain.
In situ: In situ: Fast intercalibration based on Fast intercalibration based on symmetry in minimum bias events symmetry in minimum bias events 2%2% in few hours in few hours Energy/momentum of isolated electron from WEnergy/momentum of isolated electron from W→→ e ein 2 in 2
monthsmonthsAbsolute energy scale from Z Absolute energy scale from Z → ee+ee-
Test Beam LY
Lab
o L
Y c
orr
= 4.05%
Test Beam LY – Labo LY corr
Relative channel calibration can be obtained from lab with a precision of 4 %4 %
ICHEP Beijing 2004 – R. Rusack
Monitor Laser SystemThree laser system. ND:YLF laser that pumps a Q-switched Ti-Saphire laser to monitor short term variations in the crystal transmission.
Pulse with same time structure as the scintillator at a frequency of 440 nm.
APD
F1 F2
PIN FE
LaserS
PWO
440 nm796 nm
Laser light injected at the front side of the crystals.
ICHEP Beijing 2004 – R. Rusack
Monitoring
Resolution before and after an induced large change in light output.
ICHEP Beijing 2004 – R. Rusack
Results from Test beam with final electronics.
% 0.44 MeV 142
% 2.4 )(
EEE
E430
5040)
Em(Y
Reso
luti
on
(mm
)
Energy (GeV)
1 mm
Energy (GeV)
Energy Position
0.6% at 50 GeV. 0.85 mm at 50 GeV.
Reso
luti
on
(%)