1. 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
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2. Compact Muon Solenoid CMS Weight 12,500t HCAL Muon chambers Tracker
Diameter m
Length m
Magnetic field T
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
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3. 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 nm 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
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4. 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) crystals Total crystal mass 67.4t || < 1.48
 x  = x
Endcaps 4 Dees (2 per endcap) crystals Total crystal mass 22.9t 1.48< || < 3
 x  = ↔ 0.052
Endcap Preshower Pb (2Xo,1Xo) / Si 4 Dees (2 per endcap) 4300 Si strips 1.8mm x 63mm 1.65< || < 2.6
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5. Photodetectors Barrel Avalanche photodiodes(APD)
Two 5x5 mm2 APDs/crystal
Gain 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 (B=4T) - Q.E. ~20% at 420nm
 = 26.5 mm
MESH ANODE
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6. 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
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7. 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)
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8. 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 channels, 27 July 2007
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9. 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
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10. 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
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11. 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
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12. 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
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13. Preshower detector
Motivation: Improved 0/ discrimination Rapidity coverage: < || < 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
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14. 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%
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15. 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: 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)
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16. 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= cm-2s-1)
Exploit EB precalibration for validation and tuning
Quickly improve EE intercalibration accuracy
0 resonance, Barrel ECAL 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
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17. 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
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18. Spares
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19. 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% %
p.e. stat, shower fluct, photo-detector, lateral leakage
b constant term % %
non-uniformities, inter-calibration, longitudinal leakage
c noise low L MeV MeV
high L MeV 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 fb-1
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20. 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)
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21. 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.
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22. 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 hours to calibrate 95% of barrel.
Exploit immediately after the startup!
First Resonance Observed
by CMS! (2006 Test beams)
ICHEP D J A Cockerill - RAL 22

23. 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 cm-2s-2 Red - after ~ 1 day of data taking Limit on precision due to tracker material etc
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24. 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%
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