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
(%)