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The Lead Tungstate Calorimeter for CMS R M Brown RAL - UK CALOR 2000 Annecy - France October 2000

The Lead Tungstate Calorimeter for CMS R M Brown RAL - UK CALOR 2000 Annecy - France October 2000. Outline of Talk. Overview of CMS Parameters of the ECAL Properties of Lead Tungstate Radiation levels Crystal production Photodetectors: APD, VPT Mechanical design

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The Lead Tungstate Calorimeter for CMS R M Brown RAL - UK CALOR 2000 Annecy - France October 2000

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  1. The Lead Tungstate Calorimeter for CMS R M Brown RAL - UK CALOR 2000 Annecy - France October 2000 CALOR 2000, Annecy, October 2000 R M Brown - RAL 1

  2. Outline of Talk • Overview of CMS • Parameters of the ECAL • Properties of Lead Tungstate • Radiation levels • Crystal production • Photodetectors: APD, VPT • Mechanical design • Preshower detector • Prototype performance • Monitoring system • Electronic readout system • Status summary CALOR 2000, Annecy, October 2000 R M Brown - RAL 2

  3. The Compact Muon Solenoid Detector for LHC Physics goals: SUSY, Higgs, Heavy flavours, heavy ions ECAL 1880 Scientists 150 Institutes 32 Countries Total mass : 12,500t Overall Diameter: 15.0m Overall Length: 21.6m Magnetic field: 4T CALOR 2000, Annecy, October 2000 R M Brown - RAL 3

  4. ECAL design objectives High resolution electromagnetic calorimetry is a basic design objective of CMS Benchmark physics process: Sensitivity to a low mass Higgs via H    m /m = 0.5[E1/E1  E2/E2  / tan(/2)] WhereE/E = a/E  b  c/E Aim: Barrel End cap Stochastic term: a= 2.7% 5.7%(photoelectron statistics/shower fluctuations) Constant term: b= 0.55% 0.55% (non-uniformities, shower leakage) Noise term: Low Lc= 155MeV 205MeV High L210MeV 245MeV (Angular resolution limited by uncertainty in position of interaction vertex) L=1034cm2s-1 Vertex by track finding mH=100GeV CALOR 2000, Annecy, October 2000 R M Brown - RAL 4

  5. ECAL design choices ECAL (and HCAL) within magnetic vol  Homogenous active medium (PbWO4)  Magnetic field-tolerant photodetectors with gain: - Avalanche photodiode (APD) for barrel - Vacuum phototriode (VPT) for end caps  Pb/Si Preshower detector in end caps Properties of dense inorganic scintillators CALOR 2000, Annecy, October 2000 R M Brown - RAL 5

  6. ECAL Parameters CALOR 2000, Annecy, October 2000 R M Brown - RAL 6

  7. RadiationlevelsinECAL 225 HB Relative light yield vs dose Absorbed dose after 10 years EB cm HE EE 0 0 400 cm 1.4x106 105 104 103 102 101 Gy Dose and neutron fluence • Effect of radiation on PbWO4 • (after intense R&D) • No change in scintillation properties • Small loss in transmission through • formation of colour centres • Damage saturates • Slow self-annealing occurs • Loss in light yield of a few percent • corrected with monitoring system • No damage observed with neutrons Neutron fluence (1013cm-2) Dose (kGy)  = 1.48 CALOR 2000, Annecy, October 2000 R M Brown - RAL 7

  8. Crystal production Russia (Czochralski) Preproduction (6000): 5000 delivered so far Production (30000): Order placed Delivery starts this year China (modified Bridgman-Stockbarger) R&D phase advanced Preproduction: Planned start at end of 2000 Production: Planned start in 2001 Preproduction order (Russia) Rejection rate (%) 199819992000 CALOR 2000, Annecy, October 2000 R M Brown - RAL 8

  9. Decay Time (% LY in 100ns) 500 Light Yield (p.e./MeV) 150 3500 Xtals Spec: >90% 500 Xtals Spec:>8p.e. Barrel Barrel 90 92 94 96 98 100% 0 2 4 6 8 10 12 14 16 p.e. Transmission 420 nm (%) 800 40 Light Yield (p.e./MeV) 3500 Xtals Spec: >55% 100 Xtals Barrel 6 7 8 9 10 11 12 13 p.e. 30 40 50 60 70 80% Distributions of Crystal properties End cap CALOR 2000, Annecy, October 2000 R M Brown - RAL 9

  10. Photodetectors: barrel • Avalanche photodiodes (APD) • Operated at a gain of 50 • Active area of 2x25mm2/crystal • Q.E.80% for PbWO4 emission • Excess noise factor is F=2.2 • Insensitive to shower leakage particles (deff6m) • Irradiation causes bulk leakage current to increase  electronic noise doubles after 10 yrs - acceptable Delivery from Hamamatsu starts this year CALOR 2000, Annecy, October 2000 R M Brown - RAL 10

  11. =26.5 mm MESH ANODE Photodetectors: end caps • Vacuum Phototriodes (VPT) • B-field orientation in end caps favourable for VPTs • (Tube axes 8.5o<||<25.5o with respect to field) • Vacuum devices offer greater radiation hardness than Si diodes • Gain 8-10 at B = 4T • Active area of ~280mm2/crystal • Q.E.~20% at 420nm • Excess noise factor is F~3 • Insensitive to shower leakage particles • UV glass window - less expensive than ‘quartz’ • - more radiation resistant than borosilicate glass • Irradiation causes darkening of window •  Loss in response <20% after 10 yrs-acceptable Pilot order placed with RIE (St Petersburg): 100 devices delivered so far and under test CALOR 2000, Annecy, October 2000 R M Brown - RAL 11

  12. VPT Characteristics Response vs Angle 12 10 8 6 4 2 0 Gain vs Bias Gain VA = 1000V VA = 800V 0 200 400 600 800 1000 VD (Volts) Response vs B-Field 100 90 80 60 40 20 0 Window transmission vs Dose % 300 400 500 600 700 nm CALOR 2000, Annecy, October 2000 R M Brown - RAL 12

  13. Construction: barrel Submodule: 2x5 Xtals with APD and FE electronics in 200m glass fibre alveola Module: 10x4 or 10x5 submodules mounted on a ‘Grid’, inside a ‘basket’ Supermodule: 4 Modules (1700 Xtals) Barrel= 36Supermodules Assembled Submodules CALOR 2000, Annecy, October 2000 R M Brown - RAL 13

  14. Construction: end caps • ‘Supercrystal’: carbon-fibre alveola containing • 5x5 tapered crystals + VPTs + HV filter • 160 Supercrystals per Dee • All crystals have identical dimensions • All Supercrystals are identical • (apart from inner and outer circumference) CALOR 2000, Annecy, October 2000 R M Brown - RAL 14

  15. Preshower detector • Rapidity coverage: 1.65< ||< 2.6 (End caps) • Motivation: Improved 0/ discrimination • 2 orthogonal planes of Si strip detectors behind • 2 X0 and 1 X0 Pb respectively • Strip pitch: 1.9mm (60mm long) • Area: 16.5m2 • (4300 detectors, 1.4x105 channels) Incident Direction • High radiation levels - Dose after 10 years: • ~2x1014n/cm2 • ~60kGy •  Operate at -10oC CALOR 2000, Annecy, October 2000 R M Brown - RAL 15

  16. 0/Discrimination (-jet) is potentially the most serious background to H  Track isolation cut reduces (-jet) to  50% of the intrinsic (-) background (pTcut=2GeV/c) Use 0/ discrimination in the ECAL to gain an extra margin of safety Barrel: Lateral shower shape in crystals (limited by crystal size at high E0) End cap: Cluster separation in preshower (limited by shower fluctuations at 3X0) CALOR 2000, Annecy, October 2000 R M Brown - RAL 16

  17. Test beam:Energy Resolution No preshower detector CALOR 2000, Annecy, October 2000 R M Brown - RAL 17

  18. Energyresolution with preshower Energy resolution degraded by Pb absorber - partially restored using Si p.h. information Excellent agreement between MC and data TDR performance achieved for E > 80 GeV (ET>30 GeV - OK for H  ) (even though Pb 10% too thick in this test!) CALOR 2000, Annecy, October 2000 R M Brown - RAL 18

  19. DATA LINK ADC & OPTO PREAMP APD CRYSTAL (1700/SM) DATA LINK OPTO CTRL SERIALISER CMS-ECAL MONITORING SYTEM ADC (x12) MEM 440nm/500nm 1 mJ (2x1015g) ~1.3TeV PN FE (200 Channels) LEVEL-1 LEVEL-2 SWITCH LASER FANOUT FANOUT (select SM/2) Laser Monitoring System CALOR 2000, Annecy, October 2000 R M Brown - RAL 19

  20. 1.02 1.0 0.98 0.96 0.94 1.02 1.0 0.98 0.96 0.94 0.92 Relative Response vs Time Laser-Beam Correlation Laser Resp Rel. Resp Laser  Electrons (laser corrected)  Electrons (laserandtempcorrected) 0.92 0.94 0.96 0.98 1.0 1.02 Beam Response 0 20 40 60 80 100 Time (Hours) Laser Correction for Effect of Radiation Damage CALOR 2000, Annecy, October 2000 R M Brown - RAL 20

  21. Readout architecture Upper-level VME readout (in Counting Room) Trigger Pipeline control InterfaceDAQ InterfaceTrigger PbWO4 APD Preamp Gain ADC Serialiser Optical Crystal VPT select +VCSEL link On-detector light-to-light readout • 40 MHz Clock • 12 bit precision • 4 different gains  >17 bit dynamic range CALOR 2000, Annecy, October 2000 R M Brown - RAL 21

  22. Status summary CrystalsRussia: Preproduction of 6000 Xtals on schedule Order for placed 30000 Xtals placed, delivery starts in 2001 China: Preproduction in 2000/1, full production in 2002 PhotodetectorsAPD: Preproduction completed, main production imminent VPT: Pilot order placed, delivery started MechanicsBarrel: Submodule parts in production Module: some design changes to achieve cost/performance target End cap:Procurement of supercrystal parts starts after EDR in November ElectronicsFull readout chain tested in beam in 2000 - performance OK Some problems with manufacturing yields MonitoringComponents ordered and delivery on schedule PreshowerPreproduction of Si detectors started Preamplifier prototype tested: radiation harness + performance OK Mechanics progressing well. Summary Some delays in mechanics/electronics/APD  Absorb by rescheduling Critical path defined by crystal delivery and precalibration in an electron beam CALOR 2000, Annecy, October 2000 R M Brown - RAL 22

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