The CMS Electromagnetic Calorimeter R M Brown on behalf of the CMS ECAL Group Overview Detector details Crystals Photo-detectors On-detector electronics Off-detector electronics Laser monitoring system Mechanical assembly & installation Pre-shower Inter-calibration with electrons & cosmic muons Test beam results Summary STFC RAL HEP2007 July 2007 Manchester R M Brown - RAL 1

Compact Muon Solenoid Objectives: Higgs discovery Physics beyond the Standard Model Current data suggest a light Higgs Favoured discovery channel H  gg Intrinsic width very small  Measured width, hence S/B given by experimental resolution High resolution electromagnetic calorimetry is a hallmark of CMS Target ECAL energy resolution: ≤ 0.5% above 100 GeV  120 GeV SM Higgs discovery (5s) with 10 fb-1 (100 d at 1033 cm-2s-1) Length ~ 22 m Diameter ~ 15 m Weight ~ 14.5 kt HEP2007 July 2007 Manchester R M Brown - RAL 2

ECAL: Challenges & Choices Fast response (25ns between bunch crossings) High radiation doses & neutron fluences (10 year doses: 1013 n/cm2, 1kGy (=0) 2x1014 n/cm2, 50kGy ( =2.6)) Strong magnetic field (4 Tesla) On-detector signal processing 0/ discrimination Long term reproducibility Choices: Lead tungstate crystals Avalanche photodiodes (Barrel), Vacuum phototriodes (Endcaps) Electronics in 0.25 mm CMOS Pb/Si Preshower in Endcap region Laser light monitoring system HEP2007 July 2007 Manchester R M Brown - RAL 3

ECAL layout Lead tungstate ~ 11 m3, 90 t (PbWO4) ~ 11 m3, 90 t Endcap ‘Supercystals’ (5x5 crystals) Endcap ‘Dee’ (3662 crystals) Endcaps: 1.48 < || < 3.0 4 Dees 14648 crystals (3 x 3 x 22 cm3) Barrel crystals Pb/Si Preshower Barrel ‘Supermodule’ (1700 crystals) Barrel: || < 1.48 36 Super Modules 61200 crystals (2 x 2 x 23 cm3) HEP2007 July 2007 Manchester R M Brown - RAL 4

Lead tungstate properties Radiation resistant to very high doses Light loss is characterised by ‘induced absorption’ Dynamic equilibrium between formation/annealing of colour centres under irradiation at room temp  Light loss depends on dose-rate CMS specification requires: μ420 < 1.5 m-1 (Under uniform (lateral) 60Co irradiation at > 30 Gy/hr) Under LHC-like conditions for the Barrel (~ 0.15 Gy/hr)  Light yield loss ≾ 6% 1 2 3 4 5 6 7 8 i n t a l f e r d o w v g h ( m ) T(%) - emission Fast light emission: ~80% in 25 ns Peak emission ~425 nm (visible region) Short radiation length: X0 = 0.89 cm Small Molière radius: RM = 2.10 cm 0 5 Light Yield Loss (%) Temp dependence ~2.2%/OC Stabilise to  0.05OC Low light yield (1.3% NaI) Photodetectors with gain in magnetic field DT Power-on/ Power-off HEP2007 July 2007 Manchester R M Brown - RAL 5

Photodetectors Barrel: Avalanche photodiodes (APD) 40mm deff ~6mm Barrel: Avalanche photodiodes (APD) Two 5 x 5 mm2 APDs/crystal Gain: 50 QE: ~75% @ lpeak= 420 nm Temperature dependence: - 2.4 %/oC Gain dependence on bias: 3 %/V  = 26.5 mm MESH ANODE Endcaps: Vacuum phototriodes (VPT) More radiation resistant than Si diodes (with UV glass window) - Active area ~ 280 mm2 Gain ~10 (B=4T) Q.E.~ 20% (420 nm) HEP2007 July 2007 Manchester R M Brown - RAL 6

On-detector electronics Trigger Tower (TT) Very Front End card (VFE) Front End card (FE) Trigger Sums Data MB VFE x 5 FE LVR Σ 3x3 Mean = 127 MeV Energy Equivalence (MeV) Σ 5x5 Mean = 213 MeV Σ1x1 Mean = 41.5 MeV Noise measured in Test Beam With dynamic pedestal sampling: Cluster noise scales as n for clusters summed over n channels Trigger primitives computed on the detector Command & control via token ring Modularity: Trigger Tower (25 channels in Barrel) 5 VFE Boards (5 channels each) / 1 FE Board 1 Fibre sends trig primitives (every bunch Xing) 1 Fibre sends data (on Level1 accept) x12 x6 x1 MGPA Logic 12 bit ADC 2 1 12 bits 2 bits HV APD/VPT VFE architecture for single channel HEP2007 July 2007 Manchester R M Brown - RAL 7

Laser light monitoring During LHC cycles the ECAL response will vary, depending on irradiation conditions Laser signal Electron signal (test beam) Changes in crystal transparency will be monitored with a laser allowing the ECAL response to be corrected Simulation of crystal transparency evolution at LHC (L = 2 x 1033cm-2s-1) - based on test beam irradiation results 440 nm 796 nm Laser light is injected into each crystal through optical fibres (normalised with PN diodes to 0.1 %) Blue light tracks response, infrared provides a check The laser is pulsed during the LHC ‘abort gap’ An optical switch directs light to one half-supermodule or one quarter-Dee in turn A complete monitoring cycle takes ~ 20 minutes Corrected response Raw response Time (hours) ADC 2/ndf =73.9/68 Test beam data HEP2007 July 2007 Manchester R M Brown - RAL 8

Construction & Installation: Barrel Sub-module: 10 crystals Module: 400/500 crystals Super-module: 1700 crystals Bare SM Instrumented SM HEP2007 July 2007 Manchester R M Brown - RAL 9

Barrel ECAL Installation HEP2007 July 2007 Manchester R M Brown - RAL 10

Construction & Status: Endcaps Supercrystal: 25 crystals Dee (½ endcap): 3662 crystals Front view with first 20 supercrystals mounted Rear view with laser fibre harnesses mounted Backplates successfully test mounted on HCAL Schedule 1 Endcap (2 Dees, 1 PS) ready Feb 08 inserted before CMS closes 1 Endcap early summer 08 33% HEP2007 July 2007 Manchester R M Brown - RAL 11

Rapidity coverage: 1.65 < || < 2.6 (End caps) 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: 1.9 mm (63 mm long) Area: 16.5 m2 (4300 detectors, 1.4 x105 channels) High radiation levels - Dose after 10 yrs: ~ 2 x1014 n/cm2 ~ 60 kGy  Operate at -10o C HEP2007 July 2007 Manchester R M Brown - RAL 12

Inter-calibration  2 = 0.2% s = 1.5% s = 4.5% electron beam calibration reproducibility (Aug - Sept) 9 Supermodules (25%) inter-calibrated with e-  2 = 0.2% electron beam – cosmic muon comparison s = 1.5% 36 Supermodules (100%) inter-calibrated with cosmics Cosmic muon intercalibration precision versus  ‘index’ 2.0% 1.0% electron beam - construction database comparison s = 4.5% HEP2007 July 2007 Manchester R M Brown - RAL 13

Correction for impact position 120 GeV E (GeV) Central impact (4x4 mm2) 0.5% 120 GeV ‘Uniform’ impact (20x20 mm2) after impact-position correction E (GeV) 0.5% Response for S(3x3) varies by ~3% with impact position in central crystal Correction made using information from crystals alone (works for g) Does not depend on E,, position ( ) (3 x 3) around Crystal 184 (3 x 3) around Crystal 204 (3 x 3) around Crystal 224 4x4 mm2 central region HEP2007 July 2007 Manchester R M Brown - RAL 14

Energy resolution: random impact 22 mm Series of runs at 120 GeV centred on many points within S(3x3) Results averaged to simulate the effect of random impact positions Resolution goal of 0.5% at high energy achieved HEP2007 July 2007 Manchester R M Brown - RAL 15

Summary A hallmark feature of CMS is the high resolution crystal ECAL The ECAL Barrel is complete, pre-commissioned and (almost) fully installed Crystal production has switched to the Endcaps (1/3 of crystals now delivered) The first Endcap (crystals + Preshower) to be installed at the start of 2008, the second to be ready in early summer 2008) Extensive test beam studies demonstrate the CMS ECAL will meet its ambitious design goals STFC RAL HEP2007 July 2007 Manchester R M Brown - RAL 16

Spares HEP2007 July 2007 Manchester R M Brown - RAL 17

ECAL design objectives High resolution electromagnetic calorimetry is central to the CMS design Benchmark process: H    m / m = 0.5 [E1/ E1  E2/ E2   / tan( / 2 )] Where: E / E = a /  E  b  c/ E Aim (TDR): Barrel End cap Stochastic term: a = 2.7% 5.7% (p.e. stat, shower fluct, photo-detector, lateral leakage) Constant term: b = 0.55% 0.55% (non-uniformities, inter-calibration, longitudinal leakage) Noise: Low L c = 155 MeV 770 MeV High L 210 MeV 915 MeV (dq relies on interaction vertex measurement) Coloured histograms are separate contributing backgrounds for 1fb-1 (electronic, pile-up) Optimised analysis HEP2007 July 2007 Manchester R M Brown - RAL 18

Calibration strategy Lab measurements Test Beam LY Lab LY Test Beam LY – Lab LY  = 4.0% Initial pre-calibration by ‘dead reckoning’ based on lab measurements (~4%) In-situ calibration Precision with 11M events Limit on precision 0 0.5 1.0  Inter-calibration precision % -symmetry w/jet trigger (ET > 120 GeV) Fast in-situ calibration based on principle that mean energy deposited by jet triggers is independent of  at fixed  (after correction for Tracker material) (~2-3% in few hours) Reference pre-calibration of 9 SM with 50/120 GeV electrons in test beam (<2%) Pre-calibration -ring inter-calibration and Z  e + e cross-calibration (~1% in 1 day) 70 80 90 100 GeV Z  e + e Barrel Finally: calibration to < 0.5% with W   + e in ~2 months HEP2007 July 2007 Manchester R M Brown - RAL 19

Off-Detector electronics Clock & Control System (CCS) Trigger Concentrator Card (TCC) Data Concentrator Card (DCC) HEP2007 July 2007 Manchester R M Brown - RAL 20