The CMS Electromagnetic Calorimeter

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

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

3. High Resolution calorimetry: Stochastic term 2.7%, Constant term 0.5%, Noise term 150 – 220 MeV. Large volume: 75,848 crystals covering |h| < 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 h = 0 to 2×1014 neutrons/cm2 and 50 kGy for h = 2.6. 40 MHz bunch crossing rate. Goals ICHEP Beijing 2004 – R. Rusack

4. Lead Tungstate Crystals Transmission • Radiation length – 0.83 cm • Molière radius – 2.2 cm. • Fast light output – 80% in 25 nsec. • Relative Light Yield – 1.3% NaI Emission Operate at 18o C – Temp dependence = -2.2%/OC. 350 nm No long-lived radiation damage. But short-lived metastable color centers created by radiation – careful monitoring ICHEP Beijing 2004 – R. Rusack

5. 36 Supermodules Dee 4 Dees 138 Supercrystals Construction Overview Module Submodule 10 crystals Barrel 61,200 PbWO4 crystals Readout with 122,400 APD’s Endcap 14684 crystals readout with VPT’s. ICHEP Beijing 2004 – R. Rusack

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

7. Crystals and crystal production. Light Yield Transmission at 420nm Projection is 3o off interaction point - 34 different crystal types. • All crystals are tested for: • Radiation Hardness, • Light Yield, • Physical Dimensions. • Light yield uniformity. 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

8. Photodetection 4T B-field precludes use of PMT’s.. Avalanche photodiodes in barrel. Two 5× 5 mm2 APD’s/crystal. Gain – 50. QE – 80% @ 420 nm. Temp sensitivity – -2.4%/ OC. Vacuum Phototriodes in Endcap Gain – 10. QE – 15% @ 420 nm. Rad tolerance - <10% at 20 kGy. Operates in high B – field. ICHEP Beijing 2004 – R. Rusack

9. 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. APD MGPA 3 ADC’s Front-end board GOH Trigger sums Data Supercrystal Very Front End board ICHEP Beijing 2004 – R. Rusack

10. Front-End Electronics Single channel architecture Creation of trigger primitives. Storage of data to level 1 accept. Amplifier *1 ADC Channel 2 (12bit) Trigger Link 25 FE Board Amplifier *6 ADC Channel 1 (12 bit) 14 bit Channel Data APD Crystal Data Link Amplifier *12 ADC Channel 0 (12 bit) All front-end electronics in 0.25m process. Barrel – Grouped into a 5 × 5 crystal array. Endcap – Grouped to match h - f ~100 W per trigger tower. Total power on detector ~ 50kA, 300 kW. Signal from APD’s ICHEP Beijing 2004 – R. Rusack

11. Dense multi-ribbon cable Ruggedized ribbon Off Detector Pigtail fiber Front End 12 96 12 Rx module GOH 1 1 12 12 Laser diode GOL Digital amp. ASIC PIN photo-diode array In-Line Patch Panel Distributed Patch Panel Back-end Patch Panel CMS Optical Data Links All data is sent off detector electronics via 1 GHz Optical links. Radiationhard Off detector 10,500 links for whole calorimeter – Data flow: 10 Tb/sec. ICHEP Beijing 2004 – R. Rusack

12. Cooling Radiation hard regulator has a drop out voltage of 1.5V All 0.25 m electronics runs at 2.5V. 0.45 A/channel 1 A/board 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

13. Cooling Approach: isolate crystals and APD’s from electronics. Remove heat from electronics by close coupling with water cooled bars. Trigger tower on the cooling bars Temperature stability with a 100-channel system last year. 0.04°C 2 months Crystals and APD’s dT kept to  0.05oC & uniform to 0.2oC. ICHEP Beijing 2004 – R. Rusack

14. 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. Labo LY corr s = 4.05% Test Beam LY Test Beam LY – Labo LY corr Relative channel calibration can be obtained fromlabwith a precision of4 % In situ: Fast intercalibration based on f symmetry in minimum bias events 2% in few hours Energy/momentum of isolated electron from W→ en 0.5%in 2 months Absolute energy scale from Z → e+e- ICHEP Beijing 2004 – R. Rusack

15. 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. Laser light injected at the front side of the crystals. APD PWO PIN FE 440 nm 796 nm S Laser F1 F2 ICHEP Beijing 2004 – R. Rusack

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

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