1. The CMS Electromagnetic Calorimeter Roger Rusack The University of Minnesota On behalf of the CMS ECAL collaboration

2. ICHEP Beijing 2004 – R. Rusack Detector Overview MUON BARREL CALORIMETERS Silicon Microstrips Pixels ECAL Scintillating PbWO4 crystals Cathode Strip Chambers ( ) CSC Resistive Plate Chambers ( ) RPC Drift Tube Chambers ( ) DT Resistive Plate Chambers ( ) RPC SUPERCONDUCTING COIL IRON YOKE TRACKER MUON ENDCAPS HCAL Plastic scintillator/brass sandwich

3. 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 m 3.  Operated inside a 4T magnetic field.  In a radiation environment with an integrated dose of: –10 13 neutrons/cm 2 and 1 kGy at  = 0 to 2×10 14 neutrons/cm 2 and 50 kGy for  2.6.  40 MHz bunch crossing rate.

4. ICHEP Beijing 2004 – R. Rusack Lead Tungstate Crystals Operate at 18 o C – Temp dependence = -2.2%/ O C. 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

5. ICHEP Beijing 2004 – R. Rusack Construction Overview 10 crystals Submodule Dee 138 Supercrystals 36 Supermodules 4 Dees Module Barrel 61,200 PbWO 4 crystals Readout with 122,400 APD’s Endcap 14684 crystals readout with VPT’s.

6. ICHEP Beijing 2004 – R. Rusack Preshower Two-layer silicon preshower detector placed in front of the endcap calorimeters 2 X o absorber 1 X o absorber 2mm silicon strips to separate  ’s from   ’s and for vertex identification.

7. 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 3 o 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.

8. ICHEP Beijing 2004 – R. Rusack Photodetection 4T B-field precludes use of PMT’s.. Avalanche photodiodes in barrel. Vacuum Phototriodes in Endcap Two 5× 5 mm 2 APD’s/crystal. Gain – 50. QE – 80% @ 420 nm. Temp sensitivity – -2.4%/ O C. Gain – 10. QE – 15% @ 420 nm. Rad tolerance - <10% at 20 kGy. Operates in high B – field.

9. 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 APDMGPA3 ADC’s

10. 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 ADC Channel 2 (12bit) ADC Channel 1 (12 bit) ADC Channel 0 (12 bit) 14 bit Channel Data Single channel architecture FE Board 25 Trigger 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 0.25  process.

11. ICHEP Beijing 2004 – R. Rusack Optical Data Links All data is sent off detector electronics via 1 GHz Optical links. 10,500 links for whole calorimeter – Data flow: 10 Tb/sec. Radiation hard Off detector

12. ICHEP Beijing 2004 – R. Rusack Cooling All 0.25  electronics runs at 2.5V. 0.45 A/channel 1 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%/ o C & APD gain decreases by 2.3%/ O C. Removing all excess heat is critical for the stable operation of the detector.

13. 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  0.05 o C & uniform to 0.2 o C. Temperature stability with a 100-channel system last year.

14. ICHEP Beijing 2004 – R. Rusack Test beam : precalibration We 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: Fast intercalibration based on  symmetry in minimum bias events 2% in few hours Energy/momentum of isolated electron from W→ e  in 2 months Absolute energy scale from Z ee Absolute energy scale from Z → e + e - Test Beam LY Labo LY corr  = 4.05% Test Beam LY – Labo LY corr 4 % Relative channel calibration can be obtained from lab with a precision of 4 %

15. ICHEP Beijing 2004 – R. Rusack Monitor Laser System Three 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 F1F2 PINFE Laser S PWO 440 nm 796 nm Laser light injected at the front side of the crystals.

16. ICHEP Beijing 2004 – R. Rusack Monitoring Resolution before and after an induced large change in light output.

17. ICHEP Beijing 2004 – R. Rusack Results from Test beam with final electronics. Resolution(mm) Energy (GeV) 1 mm Energy (GeV) Energy Position 0.6% at 50 GeV. 0.85 mm at 50 GeV. Resolution(%)