CMS ELECTROMAGNETIC CALORIMETER Jean-Pierre Ernenwein OVERVIEW 6th international conference on advanced technology and particle physics Villa Olmo, Como, 5 october 1998 IPN Lyon

CMS (Compact Muon Solenoid) is a general purpose detector. It will be one of the 4 experiments on the LHC : pp and heavy ions collider with E cm =14 TeV/charge CMS PHYSICS First run in 2005, for 10 years Luminosity : 30 fb -1 for 3 years Physics : Particles searches : Higgs, SUSY B physics Heavy ions

CMS ECAL PERFORMANCE Higgs physics : Needs high resolution : magnetic field of 4 T crossing at 40 MHz radiations : Gy/h in the barrel, up to 15 Gy in the endcaps AND Choice of lead tungstate crystals (fast, rad hard, density) + Avalanche PhotoDiodes (APD) in barrel (B not sensitive, gain) + Vacuum PhotoTriodes (VPT) in endcaps (rad hard, gain) Benchmark for low luminosity :

PHYSICS 130 GeV Higgs in 2 photons 130 GeV Higgs in 2 photons

LEAD TUNGSTATE : PbWO 4 26 radiation lengths in 23 cm of material (barrel), endcaps : 22 cm moliere radius of 21.9 mm, density of 8.2 g/cm 3 BUT LOW Light Yield : about 60 photons/MeV for a crystal readout with APDs (gain 50) and VPTs (gain 6-8 in 4T) low run temperature : o C to maximise LY Temperature sensitivity of crystals and APDs (~ -2%/ o C) requires a 0.1 o C temperature stabilisation. ADVANTAGES 85% of the light in 20 ns, ~ 480 nm radiation hardness : saturated loss < 5% for 0.15 Gy/h COMPACT CALORIMETER

PHOTODETECTORS APD gain curve

PHOTO DETECTORS : APDs and VPTs APDs at present time (Hamamatsu): no magnetic field sensitivity gain 50, with a voltage sensitivity of 7%/V temperature sensitivity of -2.3%/ o C quantum efficiency of 80% area of 25 mm 2 2 APDs 50 mm 2 and 4 pe/MeV radiations increase bulk current electronic noise 2 after 10 years : keep good resolution. Capacitance ~ 120 pF VPTs (Hamamatsu, RIE St. Petersbourg, Electron Tubes Ltd) : more resistant to radiations than APDs, 250 mm 2 drop of gain by a factor 2 in axial 4 T magnetic field Forseen : C ~ 100 pF, 1/M.dM/dV ~ 4-5%/V Forseen : C ~ 100 pF, 1/M.dM/dV ~ 4-5%/V

PHOTODETECTORS READOUT : P.A. + Sample ADC + optic link Transimpedance P.A. FPU : Switches of gains (1,4,8,32) to have better resolution Sampling ADC : 40 MHz, 4096 channels (A.D. 9042) One serialiser per channel (800 Mbit/s) to bring out the SADC samples with digital optic link RAD HARD ELECTRONIC (DMILL, HARRIS) with low power dissipation:

ECAL STRUCTURE GRANULARITY OF 360 (  ) x 170 (  ) crystals A submodule = 2 x 5 crystals in reflective alveola, + tablet A module = 10 x 4 (5) submodules = 400 (500) crystals, + grid + basket A supermodule = 4 modules 36 supermodules = crystals BARREL ENDCAPS 7810 x 2 crystals grouped in supercrystals (5 x 5 alveolar unit, or less) TOTAL : crystals

Calibration and Monitoring TEST BEAM CALIBRATION OF ALL CRYSTALS (CERN) in their modules, before detector installation LIGHT MONITORING TO KNOW CRYSTALS AND READOUT EVOLUTION CALIBRATION IN SITU WITH PHYSICS Within 35 days at low luminosity Mapping of all crystals Intercalibration better than 0.3 % E/p calibration with electrons measured by tracker

MONITORING

CONCLUSION PRODUCTION OF CRYSTALS HAS STARTED APDs CONSTRUCTOR HAS BEEN CHOOSEN, HIS R&D IS NEARLY COMPLETE RAD HARD ELECTRONIC READOUT WILL BE FULLY TESTED IN 1999 TECHNOLOGY OF V.F.E. IS NOT YET FIXED