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The Vacuum Phototriodes for the CMS Electromagnetic Calorimeter P R Hobson, D C Imrie, O Sharif

This paper discusses the design and performance of vacuum phototriodes (VPTs) used in the CMS Electromagnetic Calorimeter (ECAL) for the Compact Muon Solenoid (CMS) experiment. It covers the properties of lead tungstate, radiation levels, VPT performance in the end cap, and APD performance in the barrel. The paper also provides a status summary of the ECAL.

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The Vacuum Phototriodes for the CMS Electromagnetic Calorimeter P R Hobson, D C Imrie, O Sharif

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  1. The Vacuum Phototriodes for the CMS Electromagnetic Calorimeter P R Hobson, D C Imrie, O Sharif Brunel University, UK K W Bell, R M Brown, D J A Cockerill, P S Flower, B W Kennedy, A L Lintern, M Sproston, J H Williams CLRC - Rutherford Appleton Laboratory, UK (With acknowledgements to H F Heath and colleagues at Bristol University, UK and D Seliverstov and colleagues at PNPI, Russia) HEP2001 Budapest - Hungary July 2001 HEP2001, Budapest, July 2001 R M Brown - RAL 1

  2. Outline of Talk • Overview of CMS • The Electromagnetic Calorimeter (ECAL) • Properties of Lead Tungstate • Radiation levels • VPT Performance (End cap) • APD Performance (Barrel) • Status summary HEP2001, Budapest, July 2001 R M Brown - RAL 2

  3. Compact Muon Solenoid ECAL HCAL Superconducting coil Total mass : 12,500t Overall Diameter: 15.0m Overall Length: 21.6m Magnetic field: 4T HEP2001, Budapest, July 2001 R M Brown - RAL 3

  4. ECAL design objectives Benchmark physics process: Search for ~130 GeV Higgs via H    (Sensitivity depends critically on mass resoln) m /m = 0.5[E1/E1  E2/E2  / tan(/2)] WhereE/E = a/E  b  c/E Performance Aims: BarrelEnd cap Stochastic term, a: (p.e. statistics/shower fluctuation) 2.7% 5.7% Constant term, b: (non-uniformities, shower leakage) 0.55% 0.55% Noise term, c: (Electronic noise, event pile-up) Low L 155MeV 205MeV High L210MeV 245MeV (Angular resolution limited by uncertainty in position of interaction vertex) HEP2001, Budapest, July 2001 R M Brown - RAL 4

  5. Lead Tungstate Properties • Advantages: • Fast • Dense • Radiation hard • Emission in visible • Disadvantages: • Temperature dependence • Low light yield •  Photodetector with gain • (in a strong magnetic field) HEP2001, Budapest, July 2001 R M Brown - RAL 5

  6. CMS ECAL Layout Full projective geometry (‘Off-pointing’ by 3o) Barrel: 17x2 Crystal types End cap: 1 Crystal type 1290 mm 3170 mm HEP2001, Budapest, July 2001 R M Brown - RAL 6

  7. HCAL Barrel ECAL Endcap 0.2 1.2 0.35 0.5 2 ECAL Barrel 5 3 70 20 50 Doses and neutron fluences Integrated dose (kGy) and neutron fluence (x1013 cm-2) for  L = 5x105 pb-1 (~10 yrs) Black: Dose in the Crystals at the position of the shower maximum Blue: Dose behind the crystals at the position of the photodetectors Red: Neutron fluences behind the crystals HEP2001, Budapest, July 2001 R M Brown - RAL 7

  8. =26.5 mm MESH ANODE Photodetectors: end caps • B-field orientation favourable for VPTs • (Axes: 8.5o < || < 25.5o wrt to field) • More radiation hard than Si diodes • (with UV glass window) • Gain 8 -10 at B = 4 T • Active area of ~ 280 mm2/crystal • Q.E. ~ 20% at 420 nm • Vacuum Phototriode (VPT): • Single stage photomultiplier tube with fine metal gridanode HEP2001, Budapest, July 2001 R M Brown - RAL 8

  9. VPT Gain vs Dynode Voltage HEP2001, Budapest, July 2001 R M Brown - RAL 9

  10. VACUUM PHOTOTRIODE HV FILTERING ELECTRONICS CRYSTAL ‘Supercrystal’ Layout ‘Supercrystal’: carbon-fibre alveola containing 5x5 tapered crystals + VPTs + passive HV filter (160 Identical Supercrystals per Dee) Signals fed via 600 mm cable to Preamplifier + Front End electronics behind Dee Backplate HEP2001, Budapest, July 2001 R M Brown - RAL 10

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