Panic 05, 27th Oct 2005 Q. Ingram, PSI 1

The Lead TungstateElectromagnetic Calorimeter

of CMS

Q. Ingram

on behalf of the CMS Electromagnetic Calorimeter GroupAnnecy, Demokritos, Belgrade, Bhabha, Bristol, Brunel, Caltech, CERN, Cyprus, Delhi, Dubna,

Ecole Polytechnique, ETHZ, Imperial College, Ioannina, Lisbon, Lyons, Milan-Bicocca, Minnesota, Minsk, INR-Moscow, Lebedev Institute, Northeastern, Protvino, PSI, RAL, ENEA-

Rome, La Sapienza U, Saclay, Split, Taiwan Central U, Taiwan U, Turin, Yale, Yerevan

CMS, Goals, ECAL

Lead Tungstate

Photo-detectors & Electronics

Assembly

Calibration & monitoring

Test beam results

Panic 05, 27th Oct 2005 Q. Ingram, PSI 2

Compact Muon Solenoid (CMS)

21.6 m long x 15 m diameter; 12.5 k tonnes; 4 Tesla solenoid

7 TeV protons7 TeV protons

Electro-Magnetic

Calorimeter

(ECAL)

Superconducting

Solenoid (4T)

Muon Chambers Silicon Tracker Hadron Calorimeter

Return Yoke

7 TeV protons

7 TeV protons

Panic 05, 27th Oct 2005 Q. Ingram, PSI 3

Recent Photos of CMS Assembly

Muon drift chambers mountedin barrel part of the yoke

End-cap Muon cathode strip proportional chambers

Panic 05, 27th Oct 2005 Q. Ingram, PSI 4

Inserting superconducting coil into vacuum tank

Magnet inserted into the outer tank September 2005Inner vacuum tank inserted October

Coil is12.5 m long

6 m Ø

MagneticPressure(4 Tesla):

60 bar

Panic 05, 27th Oct 2005 Q. Ingram, PSI 5

Standard Model Higgs (9/05)

MH < 186 GeV, 95% C.L.

Exclusion plot from LEP working group:http://lepewwg.web.cern.ch/LEPEWWG/plots/summer2005/

H → γγ is good discovery channel

(also for lightest SUSY Higgs)

Discovery of Higgs ismajor goal of CMS.

For MH near minimumallowed by LEP (114 GeV)

Panic 05, 27th Oct 2005 Q. Ingram, PSI 6

H

1 year at High Luminosity (1.1034 cm-2.s-2 )

Background subtracted

Background irreducible – need good energy resolution

Panic 05, 27th Oct 2005 Q. Ingram, PSI 7

Resolution Goal

E/E = a /E b/E c

Aim: Barrel End cap

Stochastic term (a) 2.7% 5.7% (p.e. statistics, shower fluctuations, leakage, …)

Noise (b) 155 MeV 770 MeV Low L 210 MeV 915 MeV High L

Constant term (c) 0.55% 0.55% (gain stability, non-uniformities, inter-calibration,…)

Panic 05, 27th Oct 2005 Q. Ingram, PSI 8

LHC/ECAL Conditions

Every 25 nsec: 20 events, 1000 tracks in detector (high luminosity)

fast, high granularity, triggering capability

High radiation levels: direct from collisions. In ECAL Barrel ≤ 4 kGy 1 MeV neutron “soup” ≤ 2.1013 n cm-2

(x 10 - 50 in End-caps)

high radiation tolerance

ECAL detector is barely or practically unserviceable

very high reliability

Panic 05, 27th Oct 2005 Q. Ingram, PSI 9

ECAL

Endcaps:

14648 Crystals (1 type)

30 x 30 x 220 mm3 (24.7 X0)

Vacuum photo-triodes

Barrel: 36 Supermodules (18 per half-barrel)

61200 Crystals (34 types)

~ 24 x 24 x 230 mm3 (25.8 X0)

Avalanche photo-diodes

All channels’ gainsmonitored with laserCrystals point 3º off vertex

Pb/Silicon pre-shower for π°/γ discrimination (3 X0)

7.9 m

3.6 m

Compact, homogeneous,within magnet, precise

90 tonnes

4 Modules per Supermodule

Fast, high granularityRadiation “hard”

Panic 05, 27th Oct 2005 Q. Ingram, PSI 10

Lead Tungstate (PbWO4)

Compact calorimeter: CMS more compact, cheaper

Homogeneous calorimeter: excellent energy resolution

High density 8.28 g/cm3

Short radiation length 0.89 cm

Small Moliere radius 2.19 cm

Short decay time 10 nsec

Cost (was) 1.6 $ /cm3

Peak light emission 430 nm

Temperature Coeff - 2%/ ºC

Refractive Index ca 2.2

Light yield ~ 5% of BGO

Radiation “hard”: scintillation and emission not affected, but transmission reduced by formation of colour centres constant monitoring

Panic 05, 27th Oct 2005 Q. Ingram, PSI 11

PbWO4 Quality Control

Automatic testing of dimensions, transmission, light yield, longitudinal uniformity

Sharpness of transmission edge indicator of radiation

resistance(Crystals from Bogoroditsk,

Russia)

0

10

20

30

40

50

60

70

80

300 350 400 450 500 550 600 650 700

initialafter irradiation

wavelength (nm)

T(%

)Crystals from Shanghai all

tested after irradiation

Panic 05, 27th Oct 2005 Q. Ingram, PSI 12

Photo-Detectors (APDs, VPTs)

Requirements:

- Gain (low light yield of PbWO4)

- Operation in 4 Tesla field- Radiation hard (10 yrs: 2 1013 n/cm2 in Barrel,

> 5 1014 n/cm2 in End-caps)

- High reliability (99.9%) over 10 years - unserviceable

Solutions:-Avalanche Photo-diodes (APDs) in Barrel: gain 50 -Vacuum Photo-triodes (VPTs) in End-caps (axial field): gain 8 - 10

Both specially developed for CMS

APDs: Hamamatsu

VPTs: RIE St Petersburg

Panic 05, 27th Oct 2005 Q. Ingram, PSI 13

APD Structure

20

Photo-electrons from THIN 6 μmp-layer induce avalanche

at p-n junction

Electrons from ionising particlestraversing the bulk NOT amplified

(insensitive to shower leakage)

2 APDs (each 5 x 5 mm)mounted in capsule for gluing to crystal

Panic 05, 27th Oct 2005 Q. Ingram, PSI 14

Some APD Properties (Gain=50)

Active area 5 x 5 mmCharge collection within 20 nsec 99 ± 1%Capacitance 80 pF (fully depleted)Dark Current (Id) before irradiation < 50 nA (~ 5 nA typical)Voltage sensitivity (1/M*dM/dV) 3.15 % / VTemperature sensitivity (1/T*dM/dT) - 2.4 % / C Excess noise factor 2.1

Radiation Hardness: After 10 years LHC equivalent hadron irradiation, ONLY change is the dark current, 5 μA

Aging: No effect seen after ca 10 years’ equivalent in an oven.

Acceptance tests: to ensure 99.9% reliability, all APDs screened by 5 kGy 60Co irradiation + 4 weeks cooking at 80C

and tested to gain 300 (few % rejected)

Panic 05, 27th Oct 2005 Q. Ingram, PSI 15

Vacuum Photo-Triodes (VPTS)

• B-field orientation favourable • Gain 8 -10 at B = 4 T

• Radiation hard (UV glass window)• Active area of ~ 280 mm2/crystal• Q.E. ~ 20% at 420 nm

= 26.5 mm

MESH ANODE

Single stage photomultiplier tube with fine metal grid anode

All tested at 1.8 T (10% at 4T)

Panic 05, 27th Oct 2005 Q. Ingram, PSI 16

On-detector Electronics

800 Mb/soptical links to

upper-levelCustom designed ASICS in IBM 0.25 m technology

multi-gain shapingamplifier.

Gain 1, 6 & 12 fordynamic range

of 20000

25 ns sampling12-bit ADC with

base-line detection.

Selects gain

Build, sendtrigger

primitives;store data

(3 s latency)

Fast Xtal and

photo-detector

Crystal APD/VPT

ADCUpperLevelReadout

few ns 50 ns

Digital Trigger Sum25 channels

To ULR

To Trigger

Pipeline

Panic 05, 27th Oct 2005 Q. Ingram, PSI 17

Electronics Performance

Noise 2003 data

- 44 MeV noise in single channel (40 MeV in 2004 data)

- Negligible correlated noise

9 Crystals

25 Crystals

Resolution 120 GeV electrons Sum over 3 x 3 matrix. Only electrons entering

centre of central crystal – minimises containment and cross-calibration errors

Excellent intrinsic resolution

2004 data

Panic 05, 27th Oct 2005 Q. Ingram, PSI 18

ECAL Barrel Assembly

2 APDs in

capsule

Capsule mounted

on Xtal

10 Xtals in submodule alveolar (0.1 mm walls

glass-fibre/epoxy with Al lining) 10 kg

4 modules in each of

36 “Supermodules”

(1700 Xtals, 2 tons)

40- 50

submodules

in a module

0.5 ton

Panic 05, 27th Oct 2005 Q. Ingram, PSI 19

Adding the Electronics

Testing Tidying

Panic 05, 27th Oct 2005 Q. Ingram, PSI 20

ECAL End-Caps and Pre-Shower

25 Xtals in a “Supercrystal”

ca 40 kg

3662 Xtals in

a half-Dee

6 tons

Pre-shower Detector

1.4 x105 ch of 1.9 mm

Si strips behind Pb layers

- 10oC for rad hardness

2 half-Dees

per End-cap

Panic 05, 27th Oct 2005 Q. Ingram, PSI 21

Calibration

Pre-(inter)calibration rms

Initial channel-to-channel variation: 8%

Apply crystal light yield lab data & APD gain 4%

Calibrate in high energy electron beam < 2% no beam till 6/06

Calibrate with cosmic rays 2-3% in 1 week

In situ calibration

Intercalibrate over Φ using jet energy deposit with high (>120 GeV) ET triggers 2-3% in 2 hours

Calibrate over Φ and cross-calibrate over η with Z → e+e- 1% in 1 day

Final calibration with W → e (E/p comparison – needs Tracker) 0.5% in few months

Panic 05, 27th Oct 2005 Q. Ingram, PSI 22

Pre-Intercalibration

a) Get intercalibration coeffs. from lab light-yield

and APD gain data. Compare to beam result:

From beam

From lab

Agree to 4%

b) With cosmic rays

- Cosmic muons deposit 250 MeV OK over full length

- use adjacent crystals as veto counters

- Electronics noise 40 MeV rms: raise APD gain from 50 to 200

- 2% statistical precision in 1 week on full 1700 Supermodule channels.

ca 3% agreement (preliminary, short run) with beam results

Also vitally important full system debugger

Panic 05, 27th Oct 2005 Q. Ingram, PSI 23

Laser Monitoring

Radiation damage reduced crystal light transmission

Self-annealing (partially) restored light transmission

Net effect: light reduction saturates depending on dose rate light output varies with LHC beam conditions

Monitor transmission with laser

Light injected through fibres into each crystal

Laser stability monitored by PN diode (< 0.1%)

Panic 05, 27th Oct 2005 Q. Ingram, PSI 24

Laser Monitoring

Electron/laser pulse comparison

High beam rate(damage)

Low beam rate(recovery)

Electron (S) / laser (R) correlation:

S/S0 = (R/R0)1.6

Power ≠ 1 because laser path shorter

Panic 05, 27th Oct 2005 Q. Ingram, PSI 25

Performance in 2004 Test Beam

Resolution 120 GeV electrons Sum over 3 x 3 matrix. Uniform illumination of crystal front

Xtal 704

Energy (GeV)

E/E = 3.0 /E 166 (MeV) /E 0.35

9 Crystals

Panic 05, 27th Oct 2005 Q. Ingram, PSI 26

Schedule

Schedule is very tight, driven by crystal production

But we expect that

Barrel will be installed for pilot run in late 2007

End-caps will be installed for first physics run in 2008

Dates are subject to the LHC schedule which is also very tight

Panic 05, 27th Oct 2005 Q. Ingram, PSI 27

Summary

CMS Electromagnetic Calorimeter is

compact, precise, fast, highly granular, radiation tolerant

Major components

specially developed for ECALnew technologies (PbWO4, APDs)

- now being used in other detectors

Test with beam and monitoring system show that

performance should meet design goalsH discovery possible in 2-3 years at low luminosity

Installation in CMS “just-in-time”