2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 1

The ECAL Endcap Calorimeter for CMS

D J A CockerillRAL - UK

2002 LHC Days at SplitSplit - CroatiaOctober 2002

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 2

Outline of Talk

The CMS ECAL Endcaps Performance targets Layout Radiation Environment

Crystal Endcap Calorimeter Lead Tungstate Crystals Vacuum Phototriode

Photodetectors Design and construction

Endcap Preshower detector Silicon detectors Design & construction

Prototype performance Status summary

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 3

CMS ECAL Endcap Performance targets

High resolution electromagnetic calorimetry basic design objective of CMS

Benchmark physics process sensitivity to a low mass Higgs via H

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 4

CMS ECAL Endcap Performance targets

Higgs mass resolution, H 1 2 , target ~0.5%

m / m = 0.5 [E1/ E1 E2

/ E2 / tan( / 2 )]

where E / E = a / E b c/ E for each photon

TargetBarrel Endcap

Stochastic term a = 2.7% 5.7% Constant term b = 0.55% 0.55%

Noise term, Low L c = 155 MeV 205 MeV

High L c = 210 MeV 245

MeV

~40% of H events involve the ECAL Endcaps, MH 90-150 GeV Width of Higgs peak limited by experimental resolution

high resolution electromagnetic calorimetry homogeneous scintillating medium PbWO4 crystals – fast, dense, moderately rad hard

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 5

0/ Discrimination

( - jet) is potentially the most serious background to H Track isolation cut reduces ( - jet) to 50% of the intrinsic ( - ) background (pT cut =

2GeV/c)

Use 0/ discrimination in the ECAL to gain an extra margin of safetyBarrel: Lateral shower shape in crystals (limited by crystal size at high E0)

End cap: Cluster separation in preshower (limited by shower fluctuations at 3X0)

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 6

CMS ECAL Endcaps - Layout

EndcapElectromagneticCalorimeters

Scale

Muon chambers

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 7

Endcap Preshower1.65 < < 2.6Pb/Si detectors

ECAL Crystal Endcap1.48 < < 3.0PbWO4 crystals

HCAL Endcap

CMS ECAL Endcaps - Layout

Forward muon chambers

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 8

CMS ECAL Endcaps - Layout

Crystal ECAL Barrel

Preshower2 planes of Si2 Xo and 1 Xo Pb

4288 sensors

Crystal ECAL Endcaps14648 crystalsVol 2.7 m3

Mass 22 t

3° off-pointing,pseudo-projective geometry 3.5m

Tracker volume

3m

4T field

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 9

Radiation levels, CMS ECAL Endcaps

cm

225

00 400 cm

1.4x106 105 104 103 102 101 Gy

Dose (kGy)Neutron fluence (1013cm-2)

= 1.48

Absorbed dose

10 years, = 3 (inner edge)

200 kGy at shower max

50 kGy behind crystals

Dose rate, = 3.0

15 Gy/h, high luminosity, shower max

Dose and neutron fluence

HB

EB

EEHE

Neutron fluence

10 years, = 2.6

1.5.1014 cm-2, preshower

7.1014 cm-2 behind crystals

0.8.1014 cm-2 for electronics behind neutron moderator

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 10

Endcap PbWO4 crystals

Properties of dense inorganic scintillators

• All identical size/shape• 30 x 30 x 220 mm3

• 24.7 Xo in depth

• 2 mm taper, back to front • 25.6 mm photo-detector at rear

1” Photodetector

200 Endcap R&D xtals produced to date.

30mm

220mm

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 11

Endcap PbWO4 crystalsPbWO4 crystals produced at BTCP – Russia. 138 ovens.

Successful production of larger boules - crucial for the larger ECAL Endcap crystals 30x30 mm2 vs ~26x26 mm2 in Barrel.Larger size to reduce channel count, increased cost effectiveness

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 12

Endcap PbWO4 crystalsAt present, plant dedicated to Barrel crystal production – on CMS critical path2 Barrel crystals per boule of 65 mm diameterBarrel crystal yield 86%, productivity increase 160%

Start Endcap crystal mass production, 2 crystals per boule of 75 mm diameter, in 2003 (1000 crystals)On critical path to meet ECAL Endcap installation deadline of Jan 2007

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 13

Vacuum Phototriodes (VPTs)

ECAL Endcap within 4T magnetic volume of CMS

Require magnetic field tolerant and radiation tolerant photodetectors with gain

Vacuum phototriode (VPT) photodetectors

chosen for the ECAL Endcaps

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 14

Vacuum Phototriodes (VPTs)

B-field orientation in end caps favourable for VPTs(Tube axes 8.5o

< || < 25.5o with respect to field)

Vacuum devices offer greater radiation hardness than Si diodes

• Gain 8 - 10 at B = 4 T• Active area of ~ 280 mm2/crystal• Q.E. ~ 20% at 420 nm• Excess noise factor is F ~ 3• Insensitive to shower leakage particles

• UV glass window - less expensive than ‘quartz’ - more radiation resistant than borosilicate glass • Irradiation causes darkening of window Loss in response < 10% after 10 yrs – acceptable

Split – photocathode efficiency scans across faceplate

= 26.7 mm

MESH ANODE

26.7 mm

40 mm

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 15

VPT operation

LightCs-SbPhotocathode

10 µm pitch mesh anode (+1000V)

Dynode (+800V)

Primaryphotoelectron

Dynode gain is ~ 20 but collectionefficiency is about 50%Typical tube gain is ~10

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 16

VPT Characteristics

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0 100 200 300 400 500 600 700 800 900 1000

VD (Volts)

GA

IN

0 200 400 600 800 1000 VD (Volts)

12

10

8

6

4

2

0

Gai

n

VA = 1000V

VA = 800V

Gain vs Bias

0.5

0.6

0.7

0.8

0.9

1

300 350 400 450 500 550 600 650 700

WAVELENGTH /nm

OP

TIC

AL

TR

AN

SM

ISS

ION

0 kGy10 kGy20 kGy30 kGY20 kGy+24d Anneal

Window transmission vs Dose100

90

80

60

40

20

0

%

300 400 500 600 700 nm

Gain vs Dynode voltage for VA = 1000V and 800V

VPT Faceplate transmission

• Losses <10%, 20kGy(10 years LHC at = 2.6 over PbWO4 emission spectrum, 430 nm)

• Gains typically 8 -10• Require HT stability to ~2V

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 17

VPT Characteristics

All VPTs are measured at 0 B 1.8T and -30o 30o at RAL

1.8T Dipole Magnet at RAL 24 VPT test containers

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 18

VPT Characteristics

0 - 1.8T field

VPT angle to field, - 30o 30o

VPTs pulsed with a blue LED system at 470 nm

0.0

0.2

0.4

0.6

0.8

1.0

1.2

-90 -60 -30 0 30 60 90VPT angle (deg.)

Rel

. Ano

de R

espo

nse

Typical magnetic response

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 0.5 1 1.5 2

Magnetic Field (Tesla)

Re

l. A

no

de

Re

sp

on

se

15o

1.8T

Arrows indicate angular regions of end caps

Response vs AngleResponse vs field

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 19

VPT Characteristics

Yield, 1.8T vs P*G, 0T Yield (e/MeV), 1.8T4

70

VPT electron yield in e/MeV - normalised using test beam data

P*GP, photocathode eff.

G, Gain

VPT yields meet Endcap performance requirements

70

Yield (e/MeV)

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 20

VPT Characteristics

Production tubes

0

5

10

15

20

25

30

35

40

45

0.8 0.85 0.9 0.95 1 1.05 1.1 >1.1

Relative 4T/0T pulsed gain (upper bin edge)

Nu

mb

er

in b

in

Passed

4T batch sampling tests Relative response of VPTs at 4T at 15o to field in comparison to 0T

120 tubes OK 1 (just) outside cut

0.8

4.0T through bore Superconducting solenoid

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 21

VPT Production status

On schedule

Contract placed with Research Institute Electron (RIE), Russia

2000 – 500 pre-production devices

2001 – Mass production contract for 15,000 devices

Oct 2002 - 2600 devices delivered >1600 tested

Delivery rate 4000 per annum

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 22

Crystal Endcap Calorimeter Design and construction

 

Crystals and VPTs held in modular units called supercrystals• 5x5 array of PbWO4 crystals/VPTs• Thin walled (400m) carbon fibre alveolar unit – 330 (60%) made • HT filter cards• Optical fibres for monitoring crystal transparency

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 23

Crystal Endcap Calorimeter Design and construction

Prototype construction for Crystal Endcap beam tests in 2003

Front end electronics readout volume

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 24

14 cantilevered ‘part supercrystals’ per Dee

3662 crystals per Dee14648 crystals for the 4 DeesCrystal mass: 5.4 tonnes per Dee

138 5x5 cantilevered supercrystals per Dee

Crystal Endcap Calorimeter Design and construction

An Endcap ‘Dee’

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 25

CMS Endcap preshower detector

2 orthogonal planes of Si strip detectors behind 2 X0 and 1 X0 Pb respectively

Silicon area 16.5 m2

Incident

beam direction

Crucial to keep Si as close as possible to Pb for optimal performance

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 26

CMS Endcap preshower detector Performance targets

o→ : photon separation usually a few mm in Endcaps

For o/ discrimination: require x-y spatial reconstruction of shower to ~300 m. Achieved with Si strip detectors.

Two photons (~1cm spacing) from a 30 GeV PT

o incident on the SE/EE

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 27

CMS Endcap preshower detector

The preshower silicon micromodule4288 total, 1.4 x105 channels600 (14%) have been built and tested

63 mm

63 mm

32 Strips1.8 mm widthpitch 1.9 mm320 m p+ on n4k.cm, 300V

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 28

CMS Endcap preshower detector

Arrangement of the micromodules

Ladder for 8 micromodules

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 29

CMS Endcap preshower detector

C6F14 cooling at –15o for –5o on strips

A completed compact Endcap preshower detector2.6m , 0.2m thick

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 30

Crystal Endcap Calorimeter Design and construction

Thermal shield

Preshower

Completed Endcap

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 31

Prototype PerformanceEnergy Resolution without preshower

No preshower detector

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 32

Prototype Performance Energy resolution with preshower

Energy resolution degraded by Pb absorber

- substantially restored using Si p.h. information

Excellent agreement between MC and data

Required performance achieved for

E > 60 GeV, ET > 20 GeV OK for H

(Pb 10% thicker than final CMS, in this test)

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 33

Prototype Performance Preshower spatial resolution

Target spatial resolution of 300m achieved above 60 GeV

Spatial resolution for electrons

Excellent agreement with Monte Carlo

2002 LHC Days at Split, Split, October 2002 D J A Cockerill - RAL 34

CMS ECAL Endcaps Status summary

Crystals Mass production to start in 2003

VPTs Mass production 2600 of 14,648 (18%) Preshower Sensors mass production 600 of 4288 (14%) Mechanics Supercrystal alveolar units 330 of 560 (60%)

Monitoring system Components ordered and delivery on schedule

Dee Electronics Analogue front end, fibre optic digital readout• substantial redesign and cost optimisation in 2002• first prototypes expected in 2003

Milestones Dee1 complete 2005

Dee 2,3,4 2006

Preshower 2006

ECAL Endcaps installed in CMS Jan 2007

Mass production of ECAL Endcap components has startedMechanical design complete. A challenging schedule ahead.