The CMS Electromagnetic Calorimeter at the LHC Introduction Calorimeter design Construction and installation Calibration Conclusions D J A Cockerill on behalf of the CMS ECAL Group ICHEP 2008 D J A Cockerill - RAL 1

Compact Muon Solenoid CMS Weight 12,500t HCAL Muon chambers Tracker Diameter 15m Length 21.6m Magnetic field 3.8T HCAL Muon chambers Tracker ECAL Located inside solenoid Design benchmark H    (MH < 140 GeV/c2) Target resolution E/E ~0.5% for E>100GeV 3.8T solenoid Iron yoke ICHEP 2008 D J A Cockerill - RAL 2

Lead tungstate crystals 70% 425nm350nm 23cm 25.8Xo 22cm 24.7Xo 300nm 700nm Barrel crystal, tapered 34 types, ~2.6x2.6 cm2 at rear Endcap crystal, tapered 1 type, 3x3 cm2 at rear Emission spectrum (blue) and transmission curve Reasons for choice Homogeneous medium Fast light emission ~80% in 25 ns Short radiation length X0 = 0.89 cm Small Molière radius RM = 2.10 cm Emission peak 425nm Reasonable radiation resistance to very high doses Caveats LY temperature dependence -2.2%/OC Stabilise to  0.1OC Formation/decay of colour centres Need precise light monitoring system Low light yield (1.3% NaI) Need photodetectors with gain in magnetic field ICHEP 2008 D J A Cockerill - RAL 3

ECAL Layout Tapered crystals to provide off-pointing of ~ 3o from vertex Barrel crystals Pb/Si Endcap Preshower Endcap ‘Dee’ with ‘Supercrystals’ Barrel 36 Supermodules (18 per half barrel) 61200 crystals Total crystal mass 67.4t || < 1.48  x  = 0.0175 x 0.0175 Endcaps 4 Dees (2 per endcap) 14648 crystals Total crystal mass 22.9t 1.48< || < 3  x  = 0.01752 ↔ 0.052 Endcap Preshower Pb (2Xo,1Xo) / Si 4 Dees (2 per endcap) 4300 Si strips 1.8mm x 63mm 1.65< || < 2.6 ICHEP 2008 D J A Cockerill - RAL 4

Photodetectors Barrel Avalanche photodiodes(APD) Two 5x5 mm2 APDs/crystal Gain 50 QE ~75% Temperature dependence -2.4%/OC 40mm Endcaps Vacuum phototriodes(VPT) More radiation resistant than Si diodes - UV glass window - Active area ~ 280 mm2/crystal Gain 8 -10 (B=4T) - Q.E. ~20% at 420nm  = 26.5 mm MESH ANODE ICHEP 2008 D J A Cockerill - RAL 5

Barrel mean noise 41.5 MeV per channel Electronics Front End card (FE) Barrel Fibre optic readout at 800MHz to off detector electronics Very Front End cards (VFE) On detector readout Organised around units of 25 (5x5) crystals Electronics in radiation tolerant 0.25 m CMOS Barrel mean noise 41.5 MeV per channel Off detector Trigger Concentrator Cards (TCCs) receive FE card trigger primitives TCCs send trigger tower energy sums to Regional Calorimeter Trigger (RCT) at 40MHz Data Concentrator Card (DCC) reads FE data and TCC information upon L1 accept Performs data reduction and transfers to DAQ Multi Gain Preamp (MGPA) with 3 gain ranges Digitisation by 12 bit ADC AD41240 at 40MHz FE card sends ‘trigger primitive’ transverse energy sums at 40MHz to the counting room FE card sends data upon L1 accept ICHEP 2008 D J A Cockerill - RAL 6

Laser light monitoring system Colour centres These form in PbWO4 under irradiation Partial recovery occurs in a few hours Damage and recovery during LHC cycles tracked with a laser monitoring system 2 wavelengths: 440 nm and 796 nm 0.15% 1% Light injected into each crystal using quartz fibres, via the front (Barrel) or rear (Endcap) Laser pulse to pulse variations followed with pn diodes to 0.1% Normalise calorimeter data to the measured changes in transparency Black: during irradiation Red: after normalisation Electron signal in crystal versus time (h) ICHEP 2008 D J A Cockerill - RAL 7

CMS Barrel ECAL Submodule10 crystals Module 400/500 crystals A “naked” Supermodule with 1700 crystals Laser monitoring fibres inserted to front of each xtal Electronics and cooling installed Installation of the last SM into the first half of EB EB installation in CMS complete 61200 channels, 27 July 2007 ICHEP 2008 D J A Cockerill - RAL 8

Barrel - commissioning EB- EB+ Commissioning The 36 Supermodules of the Barrel ECAL have been fully integrated into the trigger and readout chain of CMS The detector has participated in several months of CMS cosmic runs and has recorded millions of cosmic ray events The commissioning has been extremely important for debugging the trigger and data paths and for timing in the trigger primitives CMS is now able to trigger with the full Barrel ECAL Presence of the main shaft Top SMs Bottom SMs A plot of over 3.2 million hits in the Barrel ECAL from cosmic ray triggered events in CMS ICHEP 2008 D J A Cockerill - RAL 9

Barrel - commissioning Energy 250 – 300 GeV A cosmic ray event in CMS involving the Barrel ECAL and Muon Drift Tubes A dramatic cosmic ray muon bremstrahlung in the Barrel ECAL ICHEP 2008 D J A Cockerill - RAL 10

CMS Endcap ECAL Supercrystal (SC) 25 crystals/VPTs SC assy jig EE crystals SC assy jig VPT HV cards Supercrystal mounting on a Dee backplate Cooling, electronics & optical readout mounted A completed Dee with all Supercrystals ICHEP 2008 D J A Cockerill - RAL 11

Dee1 lowering and rotation 19 July 08 CMS Endcap ECAL Dee1 lowering and rotation 19 July 08 Dee1 mounting on HE 22 July 08 Dee2 mounting on HE 24 July 08 ICHEP 2008 D J A Cockerill - RAL 12

Preshower detector Motivation: Improved 0/ discrimination Rapidity coverage: 1.65 < || < 2.6 (End caps) 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 x105channels) High radiation levels, dose after 10 yrs: 2 x 1014 n/cm2, 60 kGy => operate at -10oC A micromodule with its silicon sensor (32 channels) 90% of micromodules have been produced The first full Dee absorber with a complete complement of sensors 63mm Preshower installation expected during winter shutdown 2008/9 ICHEP 2008 D J A Cockerill - RAL 13

Energy resolution Stochastic term Constant term Noise term Barrel Barrel Energy resolution for electrons as a function of energy Data folded in from 25 3x3 arrays from a trigger tower of 25 crystals, using common intercalibration constants Electrons centrally (4mmx4mm) incident on the crystals LH plot CMS DN-2007/020 Seez et al page 10 Fig 12 RH plot NOTE2006_148 Adzic et al page 15 Fig 16 Energy resolution at 120 GeV Incident electrons from a 20x20mm2 trigger. Energy sum over 5x5 array centred on the hit crystal. Universal position correction function for the reconstructed energy applied Resolution 0.44% ICHEP 2008 D J A Cockerill - RAL 14

Beam and Cosmic Muon pre-calibration All 36 SM exposed to cosmic ray muons for ~1 week 7 SM also exposed to electrons at test beam Compare intercalibration results at test beam with those from cosmic ray muons σ = 1.55% Event: 4161 Cry: 168 Calibration coefficients from cosmic muons versus those from the test beam for 7 supermodules Muon and test beam data will provide initial intercalibration coefficients in CMS to better than ~2% with muons for 28 SM and to ~0.3% with beam for 8 SM for the Barrel ECAL Mip deposits ~250MeV (increase APD gain from 50 to 200) ICHEP 2008 D J A Cockerill - RAL 15

0 resonance, Barrel ECAL 2006 test beam In-situ Calibration Intercalibration precision at startup: Barrel ECAL <2% (0.3% in ¼ of EB) Endcap ECAL 15% Startup (inter)calibrations Rely on “fast” intercalibration procedures “Daily” -symmetry and 0 calibrations (L=2.1033 cm-2s-1) Exploit EB precalibration for validation and tuning Quickly improve EE intercalibration accuracy 0 resonance, Barrel ECAL 2006 test beam (Inter)calibrations in the long term Exploit isolated electrons Zee useful at startup after O(10 pb-1) Calibration of electron scale with Zee Calibration of photon scale with Z ICHEP 2008 D J A Cockerill - RAL 16

CMS ECAL conclusions The high resolution CMS ECAL is near to completion Barrel ECAL fully installed and commissioned Endcap ECAL Dees 1, 2 and 3 installed, Dee 4 installed by end this week Pre-shower detector installation in winter shutdown Test beam studies with 9 SMs have demonstrated excellent performance All barrel channels intercalibrated to better than 2% The Barrel ECAL has been commissioned and integrated into CMS The Barrel ECAL participates in CMS global trigger and data taking ECAL calibration strategies in place for LHC startup ICHEP 2008 D J A Cockerill - RAL 17

Spares ICHEP 2008 D J A Cockerill - RAL 18

ECAL design objectives High resolution electromagnetic calorimetry central to CMS design Benchmark process: H    m / m = 0.5 [E1/ E1  E2/ E2   / tan( / 2 )] with  resolution E / E = a /  E  b  c/ E Aims (TDR) Barrel End cap a stochastic term 2.7% 5.7% p.e. stat, shower fluct, photo-detector, lateral leakage b constant term 0.55% 0.55% non-uniformities, inter-calibration, longitudinal leakage c noise low L 155 MeV 770 MeV high L 210 MeV 915 MeV Fig 2.1 Physics TDR Results from Fig 2.10 Physics TDR A H    event in CMS with MH=120GeV Electronics, pileup Monte Carlo analyses: 5σ discovery potential for 115<MH<140GeV with 8 -16 fb-1 ICHEP 2008 D J A Cockerill - RAL 19

Off-Detector electronics TTC Trigger and Timing Card TTS Trigger Throttling System mFEC mezzanine Front End Controller card (connects to FE card via token ring) SLB Synchronisation and Link Board mezzanine Clock & Control System Card (CCS) Selective Readout Processor (SRP) Trigger Concentrator Card (TCC) Data Concentrator Card (DCC) ICHEP 2008 D J A Cockerill - RAL 20

π0 Calibration Concept p0 Calibration Data after L1 Trigger Online Farm p0 Calibration >10 kHz ~1 kHz Level 1 trigger rate dominated by QCD: several π0s/event Useful π0γγ decays selected online from such events Main advantage: high π0 rate (nominal L1 rate is 100kHz !) “Design” calibration precision  better than 0.5% Achieving it would be crucial for the Hγγ detection Studies performed with about four million fully simulated QCD events. Results given for the scenario of L=2x1033cm-2s-1 and L1 rate of 10 kHz. ICHEP 2008 D J A Cockerill - RAL 21

Calibration of CMS ECAL using π0γγ Decays Barrel study at L=2x1033cm-2s-1 π0γγ rate of 1.5 kHz 2,100 π0/crystal/day, signal-to-background ≈ 2.0. Only 20 - 80 hours to calibrate 95% of barrel. Exploit immediately after the startup! First Resonance Observed by CMS! (2006 Test beams) ICHEP 2008 D J A Cockerill - RAL 22 22

In-situ Calibration Strategy at startup – Phi symmetry Rapid achievement of ~2% intercalibration  symmetry of energy deposition ( intercalibration) in rings of crystals L1 triggers – single crystals, 1-6 GeV transverse energy (barrel) Precision (%) 2% 4% ****** NOT FINAL ****** Monte Carlo results using notional tracker material budget estimates only Barrel Eta Endcap Eta Blue – after a few hours of data taking, luminosity 2.1033 cm-2s-2 Red - after ~ 1 day of data taking Limit on precision due to tracker material etc ICHEP 2008 D J A Cockerill - RAL 23

Intercalibration from Laboratory Measurements During assembly, all detector components are characterised Thus the relative calibration ci of each channel may be estimated: Where: LY is crystal light yield, M and eQ are gain and quantum efficiency of the photo-detectors cele is the calibration of the electronics chain Ratio: Test beam/Lab Test beam vs Lab Intercalibration s = 4.2% ICHEP 2008 D J A Cockerill - RAL 24