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The Lead Tungstate Electromagnetic Calorimeter of CMS

The Lead Tungstate Electromagnetic Calorimeter of CMS. Q. Ingram on behalf of the CMS Electromagnetic Calorimeter Group

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The Lead Tungstate Electromagnetic Calorimeter of CMS

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  1. The Lead TungstateElectromagnetic Calorimeterof CMS • Q. Ingram • on behalf of the CMS Electromagnetic Calorimeter Group • Annecy, Demokritos, Belgrade, Bhabha, Bristol, Brunel, Caltech, CERN, Cyprus, Delhi, Dubna, Ecole Polytechnique, ETHZ, Imperial College, Ioannina, Lisbon, Lyons, Milan-Bicocca, Minnesota, Minsk, INR-Moscow, Lebedev Institute, Northeastern, Protvino, PSI, RAL, ENEA-Rome, La Sapienza U, Saclay, Split, Taiwan Central U, Taiwan U, Turin, Yale, Yerevan • CMS, Goals, ECAL • Lead Tungstate • Photo-detectors & Electronics • Assembly • Calibration & monitoring • Test beam results Q. Ingram, PSI

  2. Muon Chambers Hadron Calorimeter Silicon Tracker Electro- Magnetic Calorimeter (ECAL) 7 TeV protons 7 TeV protons Superconducting Solenoid (4T) Return Yoke Compact Muon Solenoid (CMS) 7 TeV protons 7 TeV protons 21.6 m long x 15 m diameter; 12.5 k tonnes; 4 Tesla solenoid Q. Ingram, PSI

  3. Recent Photos of CMS Assembly Muon drift chambers mounted in barrel part of the yoke End-cap Muon cathode strip proportional chambers Q. Ingram, PSI

  4. Inserting superconducting coil into vacuum tank Magnetic Pressure (4 Tesla): 60 bar Coil is 12.5 m long 6 m Ø Magnet inserted into the outer tank September 2005 Inner vacuum tank inserted October Q. Ingram, PSI

  5. Discovery of Higgs is major goal of CMS. For MHnear minimum allowed by LEP (114 GeV) H →γγis good discovery channel (also for lightest SUSY Higgs) Standard Model Higgs (9/05) MH < 186 GeV, 95% C.L. Exclusion plot from LEP working group: http://lepewwg.web.cern.ch/LEPEWWG/plots/summer2005/ Q. Ingram, PSI

  6. H  1 year at High Luminosity (1.1034 cm-2.s-2 ) Background subtracted Background irreducible – need good energy resolution Q. Ingram, PSI

  7. Resolution Goal E/E = a/E  b/E  c Aim: Barrel End cap Stochastic term (a) 2.7% 5.7% (p.e. statistics, shower fluctuations, leakage, …) Noise (b)155 MeV 770 MeV Low L 210 MeV 915MeV High L Constant term (c) 0.55% 0.55% (gain stability, non-uniformities, inter-calibration,…) Q. Ingram, PSI

  8. LHC/ECAL Conditions Every 25 nsec: 20 events, 1000 tracks in detector (high luminosity)  fast, high granularity, triggering capability High radiation levels: direct from collisions. In ECAL Barrel ≤ 4 kGy 1 MeV neutron “soup” ≤ 2.1013 n cm-2 (x 10 - 50 in End-caps)  high radiation tolerance ECAL detector is barely or practically unserviceable  very high reliability Q. Ingram, PSI

  9. Compact, homogeneous, within magnet, precise Barrel: 36 Supermodules (18 per half-barrel) 61200 Crystals (34 types) ~ 24 x 24 x 230 mm3 (25.8 X0) Avalanche photo-diodes Fast, high granularity Radiation “hard” 4 Modules per Supermodule 90 tonnes Endcaps: 14648 Crystals (1 type) 30 x 30 x 220 mm3 (24.7 X0) Vacuum photo-triodes Pb/Silicon pre-shower for π°/γ discrimination (3 X0) 3.6 m 7.9 m All channels’ gains monitored with laser Crystals point 3º off vertex ECAL Q. Ingram, PSI

  10. Lead Tungstate (PbWO4) High density 8.28 g/cm3 Short radiation length 0.89 cm Small Moliere radius 2.19 cm Short decay time 10 nsec Cost (was) 1.6 $ /cm3 Peak light emission 430 nm Temperature Coeff - 2%/ ºC Refractive Index ca 2.2 Light yield ~ 5% of BGO Radiation“hard”: scintillation and emission not affected, but transmission reduced by formation of colour centres constant monitoring Compact calorimeter: CMS more compact, cheaper Homogeneous calorimeter: excellent energy resolution Q. Ingram, PSI

  11. 8 0 7 0 6 0 T(%) 5 0 4 0 i n i t i a l 3 0 a f t e r i r r a d i a t i o n 2 0 1 0 0 3 0 0 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 w a v e l e n g t h ( n m ) PbWO4 Quality Control Sharpness of transmission edge indicator of radiation resistance (Crystals from Bogoroditsk, Russia) Automatic testing of dimensions, transmission, light yield, longitudinal uniformity Crystals from Shanghai all tested after irradiation Q. Ingram, PSI

  12. Photo-Detectors (APDs, VPTs) • Requirements: • Gain (low light yield of PbWO4) • Operation in 4 Tesla field • Radiation hard (10 yrs: 2 1013 n/cm2 in Barrel, • > 5 1014 n/cm2in End-caps) • - High reliability (99.9%) over 10 years - unserviceable • Solutions: • Avalanche Photo-diodes (APDs) in Barrel: gain 50 • Vacuum Photo-triodes (VPTs) in End-caps (axial field): gain 8 - 10 • Both specially developed for CMS • APDs: Hamamatsu • VPTs: RIE St Petersburg Q. Ingram, PSI

  13. APD Structure Photo-electrons from THIN 6 μm p-layer induce avalanche at p-n junction Electrons from ionising particles traversing the bulk NOT amplified (insensitive to shower leakage) 2 APDs (each 5 x 5 mm) mounted in capsule for gluing to crystal Q. Ingram, PSI

  14. Some APD Properties (Gain=50) • Active area 5 x 5 mm • Charge collection within 20 nsec 99 ± 1% • Capacitance 80 pF (fully depleted) • Dark Current (Id) before irradiation < 50 nA(~ 5 nA typical) • Voltage sensitivity (1/M*dM/dV) 3.15 % / V • Temperature sensitivity (1/T*dM/dT) - 2.4 % / C • Excess noise factor 2.1 Radiation Hardness:After 10 years LHC equivalent hadron irradiation, ONLY change is the dark current,  5 μA Aging:No effect seen after ca 10 years’ equivalent in an oven. Acceptance tests:to ensure 99.9% reliability, all APDs screened by 5 kGy 60Co irradiation + 4 weeks cooking at 80C and tested to gain 300 (few % rejected) Q. Ingram, PSI

  15. =26.5 mm MESH ANODE Vacuum Photo-Triodes (VPTS) • B-field orientation favourable • Gain 8 -10 at B = 4 T • Radiation hard (UV glass window) • Active area of ~ 280 mm2/crystal • Q.E. ~ 20% at 420 nm Single stage photomultiplier tube with fine metal gridanode All tested at 1.8 T (10% at 4T) Q. Ingram, PSI

  16. Pipeline Upper Level Readout ADC To ULR Crystal APD/VPT To Trigger S Digital Trigger Sum 25 channels 50 ns few ns On-detector Electronics Build, send trigger primitives; store data (3 s latency) multi-gain shaping amplifier. Gain 1, 6 & 12 for dynamic range of 20000 25 ns sampling 12-bit ADC with base-line detection. Selects gain Fast Xtal and photo- detector 800 Mb/soptical links to upper-level Custom designed ASICS in IBM 0.25m technology Q. Ingram, PSI

  17. 9 Crystals 2004 data 25 Crystals Electronics Performance Resolution 120 GeV electrons Sum over 3 x 3 matrix. Only electrons entering centre of central crystal – minimises containment and cross-calibration errors Noise 2003 data obsolete obsolete obsolete - 44 MeV noise in single channel (40 MeV in 2004 data) - Negligible correlated noise Excellent intrinsic resolution Q. Ingram, PSI

  18. ECAL BarrelAssembly 40- 50 submodules in a module 0.5 ton 2 APDs in capsule Capsule mounted on Xtal 10 Xtals in submodule alveolar (0.1 mm walls glass-fibre/epoxy with Al lining) 10 kg 4 modules in each of 36 “Supermodules” (1700 Xtals, 2 tons) Q. Ingram, PSI

  19. Adding the Electronics Testing Tidying Q. Ingram, PSI

  20. 25 Xtals in a “Supercrystal” ca 40 kg 2 half-Dees per End-cap Pre-shower Detector 1.4 x105 ch of 1.9 mm Si strips behind Pb layers - 10oC for rad hardness 3662 Xtals in a half-Dee 6 tons ECAL End-Caps and Pre-Shower Q. Ingram, PSI

  21. Calibration Pre-(inter)calibrationrms Initial channel-to-channel variation: 8% Apply crystal light yield lab data & APD gain 4% Calibrate in high energy electron beam < 2% no beam till 6/06 Calibrate with cosmic rays 2-3% in 1 week In situ calibration Intercalibrate over Φusing jet energy deposit with high (>120 GeV) ET triggers 2-3% in 2 hours Calibrate over Φ and cross-calibrate over η with Z → e+e- 1% in 1 day Final calibration with W → e  (E/p comparison – needs Tracker) 0.5% in few months Q. Ingram, PSI

  22. b) With cosmic rays • Cosmic muons deposit 250 MeVOK • over full length • - use adjacent crystals as • veto counters • - Electronics noise 40 MeV rms: • raise APD gain from 50 to 200 • - 2% statistical precision in 1 week on • full 1700 Supermodule channels. • ca 3% agreement (preliminary, short run) • with beam results • Also vitally important full system debugger a) Get intercalibration coeffs. from lab light-yield and APD gain data. Compare to beam result: From beam From lab Agree to 4% Pre-Intercalibration Q. Ingram, PSI

  23. Laser Monitoring Radiationdamage  reduced crystal light transmission Self-annealing  (partially) restored light transmission Net effect: light reduction saturates depending on dose rate light output varies with LHC beam conditions Monitor transmission with laser Light injected through fibres into each crystal Laser stability monitored by PN diode (< 0.1%) Q. Ingram, PSI

  24. Low beam rate (recovery) High beam rate (damage) Laser Monitoring Electron/laser pulse comparison Electron (S) / laser (R) correlation: S/S0 = (R/R0)1.6 Power ≠ 1 because laser path shorter Q. Ingram, PSI

  25. E/E = 3.0 /E  166 (MeV) /E  0.35 Energy (GeV) Performance in 2004 Test Beam Resolution 120 GeV electrons Sum over 3 x 3 matrix. Uniform illumination of crystal front obsolete obsolete Xtal 704 obsolete 9 Crystals Q. Ingram, PSI

  26. Schedule • Schedule is very tight, driven by crystal production • But we expect that • Barrel will be installed for pilot run in late 2007 • End-caps will be installed for first physics run in 2008 • Dates are subject to the LHC schedule which is also very tight Q. Ingram, PSI

  27. Summary • CMS Electromagnetic Calorimeter is • compact, precise, fast, highly granular, radiation tolerant • Major components • specially developed for ECAL • new technologies (PbWO4, APDs) • - now being used in other detectors • Test with beam and monitoring system show that • performance should meet design goals • H   discovery possible in 2-3 years at low luminosity • Installation in CMS “just-in-time” Q. Ingram, PSI

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