CMS ECAL

ICHEP 2008 D J A Cockerill - RAL 1

The CMS Electromagnetic Calorimeter at the LHC

D J A Cockerillon behalf of the CMS ECAL Group

Introduction Calorimeter design Construction and installation Calibration Conclusions

CMS ECAL

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Compact Muon Solenoid

ECALLocated inside solenoid

Design benchmarkH (MH < 140 GeV/c2)

Target resolution E/E ~0.5% for E>100GeV

Tracker

Muon chamber

s

HCAL

Iron yoke

3.8T solenoi

d

CMSWeight 12,500tDiameter 15mLength 21.6mMagnetic field 3.8T

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Lead tungstate crystals

CaveatsLY 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

Reasons for choice Homogeneous mediumFast 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

23cm 25.8Xo 22cm

24.7Xo

Barrel crystal, tapered34 types, ~2.6x2.6 cm2 at rear

Endcap crystal, tapered1 type, 3x3 cm2 at rear

Emission spectrum (blue)and transmission curve

425nm350nm

70%

300nm 700nm

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ECAL Layout

Barrel36 Supermodules (18 per half barrel)61200 crystalsTotal crystal mass 67.4t|| < 1.48

x = 0.0175 x 0.0175

Tapered crystals to provide off-pointing of ~ 3o from vertex

Endcap PreshowerPb (2Xo,1Xo) / Si 4 Dees (2 per endcap)4300 Si strips1.8mm x 63mm1.65< || < 2.6

Endcaps4 Dees (2 per endcap)14648 crystals Total crystal mass 22.9t1.48< || < 3

x = 0.01752 ↔ 0.052

Barrel crystals

Pb/Si EndcapPreshower

Endcap ‘Dee’ with ‘Supercrystals’

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Photodetectors

BarrelAvalanche photodiodes(APD)Two 5x5 mm2 APDs/crystalGain 50 QE ~75%Temperature dependence -2.4%/OC

40m

EndcapsVacuum 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

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Electronics

On detector readoutOrganised around units of 25 (5x5) crystalsElectronics in radiation tolerant 0.25 m CMOS

Multi Gain Preamp (MGPA) with 3 gain rangesDigitisation 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

Barrel

Barrel mean noise 41.5 MeV per channel

Off detectorTrigger 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 dataand TCC information upon L1 acceptPerforms data reduction and transfers to DAQ

Very Front Endcards (VFE)

Front End card (FE)

Fibre optic readout at 800MHz to off detector electronics

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Laser light monitoring system

Light injected into each crystal using quartz fibres, via the front (Barrel) or rear (Endcap)

Laser pulse to pulse variations followedwith pn diodes to 0.1%

Normalise calorimeter data to the measured changes in transparency

F1 F2

PIN FE

LaserS

PWO

F1 F2

PIN FE

LaserS

PWO

Colour centresThese 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

Black: during irradiationRed: after normalisation

1%

0.15%

Electron signal in crystal versus time (h)

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CMS Barrel ECAL

Submodule10 crystals

A “naked” Supermodule

with 1700 crystals

Module 400/500 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 complete61200 channels, 27 July 2007

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Barrel - commissioning

A plot of over 3.2 million hits in the BarrelECAL from cosmic ray triggered events in CMS

Top SMs

Bottom SMs

EB- EB+

Presence of the main shaft

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

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Barrel - commissioning

A cosmic ray event in CMS involving the Barrel ECAL and Muon Drift Tubes

A dramatic cosmic ray muon bremstrahlung in the Barrel ECAL

Energy250 – 300 GeV

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CMS Endcap ECAL

Supercrystal mounting on a Dee backplate

Supercrystal (SC)25 crystals/VPTs

A completed Dee with all Supercrystals

SC assy jig VPT HV cards

SC assy jig EE crystals

Cooling, electronics & optical readout mounted

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CMS Endcap ECAL

Dee1 mounting on HE22 July 08

Dee2 mounting on HE24 July 08

Dee1 lowering and rotation 19 July 08

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Preshower detectorMotivation: Improved 0/ discriminationRapidity 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

63mmThe first full Dee absorber with a complete complement of sensors

Preshower installation expected during winter shutdown 2008/9

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Energy resolution

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

Stochastic term

Constant term

Noise term

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%

Barrel Barrel

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Mip deposits ~250MeV(increase APD gain from 50 to 200)

Beam and Cosmic Muon pre-calibration

Event: 4161 Cry: 168

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%

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

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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 termExploit isolated electronsZee useful at startup after O(10 pb-1)

Calibration of electron scale with Zee

Calibration of photon scale with Z

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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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Spares

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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

ECAL design objectives

A H event in CMS with MH=120GeV

High resolution electromagneticcalorimetry 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

Monte Carlo analyses: 5σ discovery potential for 115<MH<140GeV with 8 -16 fb-1

Electronics, pileup

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Off-Detector electronics

Clock & Control System Card (CCS)

Data Concentrator Card (DCC)

Trigger Concentrator Card (TCC)

Selective Readout Processor (SRP)

TTC Trigger and Timing CardTTS Trigger Throttling SystemmFEC mezzanine Front End Controller card (connects to FE card via token ring)SLB Synchronisation and Link Board mezzanine

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π0 Calibration Concept

• Level 1 trigger rate dominated by QCD: several π0s/event

• Useful π0γγ 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 Hγγ 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.

Data after L1 Trigger Online Farm 0 Calibration

>10 kHz~1 kHz

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22

Calibration of CMS ECAL using π0γγ Decays

Barrel study at L=2x10L=2x103333cmcm-2-2ss-1 -1 π0γγ rate of 1.5 kHzrate of 1.5 kHz 2,100 2,100 ππ00/crystal/day, signal-to-background /crystal/day, signal-to-background ≈ 2.0.≈ 2.0.Only 20 - 80 hours to calibrate 95% of barrel.Only 20 - 80 hours to calibrate 95% of barrel.Exploit immediately after the startup!Exploit immediately after the startup!

First Resonance Observed by CMS! (2006 Test beams)

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In-situ CalibrationStrategy at startup – Phi symmetry

Rapid achievement of ~2% intercalibration symmetry of energy deposition ( intercalibration) in rings of crystalsL1 triggers – single crystals, 1-6 GeV transverse energy (barrel)

Blue – after a few hours of data taking, luminosity 2.1033 cm-2s-2

Red - after ~ 1 day of data takingLimit on precision due to tracker material etc

Pre

cisi

on

(%

)

2%

4%

Barrel Eta Endcap Eta

****** NOT FINAL ******

Monte Carlo results using

notional tracker material

budget estimates only

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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 Q are gain and quantum efficiency of the photo-detectors

cele is the calibration of the electronics chain

Intercalibration from Laboratory Measurements

= 4.2%Test beam vs Lab IntercalibrationRatio:Test beam/Lab