the cms electromagnetic calorimeter

The CMS Electromagnetic Calorimeter

Roger Rusack

The University of Minnesota

On behalf of the CMS ECAL collaboration

ICHEP Beijing 2004 – R. Rusack

Detector Overview

MUON BARREL

CALORIMETERS

Silicon MicrostripsPixels

ECAL Scintillating PbWO4 crystals

Cathode Strip Chambers ( )CSCResistive Plate Chambers ( )RPC

Drift Tube Chambers ( ) DT

Resistive Plate Chambers ( )RPC

SUPERCONDUCTINGCOIL

IRON YOKE

TRACKER

MUONENDCAPS

HCAL

Plastic scintillator/brasssandwich


Goals

High Resolution calorimetry:

– Stochastic term 2.7%, Constant term 0.5%, Noise term 150 – 220 MeV. Large volume:

– 75,848 crystals covering || < 2.6.

– 90.8 tons of crystals or 10.9 m3. Operated inside a 4T magnetic field. In a radiation environment with an integrated dose of:

– 1013 neutrons/cm2 and 1 kGy at = 0 to 2×1014 neutrons/cm2 and 50 kGy for 2.6.

40 MHz bunch crossing rate.


Lead Tungstate Crystals

Operate at 18o C – Temp dependence = -2.2%/OC.

•Radiation length – 0.83 cm•Molière radius – 2.2 cm.•Fast light output – 80% in 25 nsec.•Relative Light Yield – 1.3% NaI

No long-lived radiation damage.

But short-lived metastable color centers created by radiation – careful monitoring

Transmission

Emission

350 nm


Construction Overview

10 crystals

Submodule

Dee

138 Supercrystals

36 Supermodules

4 Dees

Module

Barrel61,200 PbWO4

crystalsReadout with 122,400 APD’s

Endcap14684 crystals

readout with VPT’s.


PreshowerTwo-layer silicon preshower detector placed in front of the endcap calorimeters

2 Xo absorber 1 Xo absorber

2mm silicon strips to separate ’s from ’s and for vertex identification.


Crystals and crystal production.

Transmission at 420nm Light Yield

All crystals are tested for:• Radiation Hardness,• Light Yield,• Physical Dimensions.• Light yield uniformity.

Projection is 3o off interaction point - 34 different crystal types.

Barrel Crystals are tapered – variation of reponse with origin of the shower.

Correct by roughening one surface of the crystal.


Photodetection4T B-field precludes use of PMT’s..

Avalanche photodiodes in barrel.

Vacuum Phototriodes in Endcap

Two 5× 5 mm2 APD’s/crystal.Gain – 50.QE – 80% @ 420 nm.Temp sensitivity – -2.4%/ OC.

Gain – 10.QE – 15% @ 420 nm.Rad tolerance - <10% at 20 kGy.Operates in high B – field.


Readout Overview• Each crystal has a low-noise, large dynamic range pre-amplifier with three gain outputs each coupled to a separate 40 MHz ADC, to cover the full 50 MeV to 1 TeV range.

• Level 1 trigger sums are sent every bunch crossing.

• Data from each crossing is stored until level 1 trigger accept.

•All data are sent on fiber optic links.

Supercrystal

Front-end board

Data

Trigger sums

Very Front End board

GOH

APD MGPA 3 ADC’s


Front-End Electronics

Barrel – Grouped into a 5 × 5 crystal array.Endcap – Grouped to match

Crystal APD

Amplifier*1

Amplifier*6

Amplifier*12

ADCChannel2 (12bit)

ADCChannel1 (12 bit)

ADCChannel0 (12 bit)

14 bitChannel

Data

Single channel architecture

FE Board

25Trigger Link

Data Link

Creation of trigger primitives.Storage of data to level 1 accept.

Signal from APD’s

~100 W per trigger tower.Total power on detector ~ 50kA, 300 kW.

All front-end electronics in 0.25process.


Optical Data Links

All data is sent off detector electronics via 1 GHz Optical links.

12Rx moduleRx module

12

1GOHGOH1212

1

96

DistributeDistributed Patch d Patch PanelPanel

Back-end Back-end Patch Patch PanelPanel

Off DetectorOff DetectorFront EndFront End Pigtail Pigtail

fiberfiber

RuggedizeRuggedized ribbond ribbon

Dense Dense multi-multi-ribbon ribbon cablecable

GOLGOL Laser Laser diodediode In-Line In-Line

Patch Patch PanelPanel

CMCMSS

PIN photo-PIN photo-diode diode arrayarray

Digital Digital amp. amp. ASICASIC

1212

10,500 links for whole calorimeter – Data flow: 10 Tb/sec.

Radiation hardOff detector


Cooling

All 0.25 electronics runs at 2.5V.

0.45 A/channel1 A/board

Radiation hard regulator has a drop out voltage of 1.5V

Total power in whole calorimeter ~300 kW

Crystal light yield decreases by 2.2%/oC & APD gain decreases by 2.3%/OC.

Removing all excess heat is critical for the stable operation of the detector.


Cooling

Trigger tower on the cooling bars

0.04°C

2 months

Approach: isolate crystals and APD’s from electronics.Remove heat from electronics by close coupling with water cooled bars.

Crystals and APD’s kept to 0.05oC & uniform to 0.2oC.

Temperature stability with a 100-channel system last year.


Test beam : precalibrationWe cannot test calibrate every crystal with an electron beam.

Obtain a first calibration point from component data: crystal light yield, APD & pre-amplifer gain.

In situ: In situ: Fast intercalibration based on Fast intercalibration based on symmetry in minimum bias events symmetry in minimum bias events 2%2% in few hours in few hours Energy/momentum of isolated electron from WEnergy/momentum of isolated electron from W→→ e ein 2 in 2

monthsmonthsAbsolute energy scale from Z Absolute energy scale from Z → ee+ee-

Test Beam LY

Lab

o L

Y c

orr

= 4.05%

Test Beam LY – Labo LY corr

Relative channel calibration can be obtained from lab with a precision of 4 %4 %


Monitor Laser SystemThree laser system. ND:YLF laser that pumps a Q-switched Ti-Saphire laser to monitor short term variations in the crystal transmission.

Pulse with same time structure as the scintillator at a frequency of 440 nm.

APD

F1 F2

PIN FE

LaserS

PWO

440 nm796 nm

Laser light injected at the front side of the crystals.


Monitoring

Resolution before and after an induced large change in light output.


Results from Test beam with final electronics.

% 0.44 MeV 142

% 2.4 )(

EEE

E430

5040)

Em(Y

Reso

luti

on

(mm

)

Energy (GeV)

1 mm

Energy (GeV)

Energy Position

0.6% at 50 GeV. 0.85 mm at 50 GeV.

Reso

luti

on

(%)

the cms electromagnetic calorimeter

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