Transcript Document 7316966

The CMS Electromagnetic Calorimeter at
the LHC
CMS ECAL
Introduction
Construction and installation
Calorimeter design
Calibration
Conclusions
D J A Cockerill
on behalf of the CMS ECAL Group
ICHEP 2008
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Compact Muon Solenoid
CMS ECAL
CMS
HCAL
Weight
12,500t
Diameter
15m
Length
21.6m
Magnetic field 3.8T
Muon
chambers
Tracker
ECAL
Located inside solenoid
Design benchmark
H    (MH < 140 GeV/c2)
Target resolution
E/E ~0.5% for E>100GeV
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3.8T
solenoid
Iron yoke
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Lead tungstate crystals
CMS ECAL
70%
23cm
25.8Xo
22cm
24.7Xo
Barrel crystal, tapered
34 types, ~2.6x2.6 cm2 at rear
Reasons for choice
Homogeneous medium
Fast light emission
Short radiation length
Small Molière radius
Emission peak
Endcap crystal, tapered
1 type, 3x3 cm2 at rear
~80% in 25 ns
X0 = 0.89 cm
RM = 2.10 cm
425nm
Reasonable radiation resistance to very
high doses
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425nm
350nm
300nm
700nm
Emission spectrum (blue)
and transmission curve
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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ECAL Layout
CMS ECAL
Tapered crystals to
provide off-pointing
of ~ 3o from vertex
Barrel crystals
Pb/Si Endcap
Preshower
Endcap ‘Dee’ with
‘Supercrystals’
Barrel
Endcaps
Endcap Preshower
36 Supermodules (18 per half barrel)
61200 crystals
Total crystal mass 67.4t
|| < 1.48
 x  = 0.0175 x 0.0175
4 Dees (2 per endcap)
14648 crystals
Total crystal mass 22.9t
1.48< || < 3
 x  = 0.01752 ↔ 0.052
Pb (2Xo,1Xo) / Si
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4 Dees (2 per endcap)
4300 Si strips
1.8mm x 63mm
1.65< || < 2.6
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Photodetectors
Barrel
Avalanche photodiodes(APD)
CMS ECAL
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Two 5x5 mm2 APDs/crystal
Gain 50
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 8 -10 (B=4T)
- Q.E. ~20% at 420nm
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 = 26.5 mm
MESH ANODE
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Electronics
CMS ECAL
Front End
card (FE)
Barrel
Fibre optic readout at
800MHz to off detector
Very Front End
electronics
cards (VFE)
On detector readout
Organised around units of 25 (5x5) crystals
Electronics in radiation tolerant 0.25 mm CMOS
Barrel mean noise 41.5 MeV per channel
Off detector
Trigger Concentrator Cards (TCCs) receive FE
card trigger primitives
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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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
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Laser light monitoring system
CMS ECAL
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
PWO
PIN
F1
FE
0.15%
F2
S
Laser
Light injected into each crystal using quartz
fibres, via the front (Barrel) or rear (Endcap)
1%
Black: during irradiation
Red: after normalisation
Laser pulse to pulse variations followed
with pn diodes to 0.1%
Normalise calorimeter data to the measured
changes in transparency
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Electron signal in crystal
versus time (h)
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CMS Barrel ECAL
Submodule
10 crystals
Module
400/500 crystals
Electronics and
cooling installed
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CMS ECAL
A “naked” Supermodule Laser monitoring fibres
with 1700 crystals
inserted to front of each xtal
Installation of the last SM into
the first half of EB
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EB installation in CMS complete
61200 channels, 27 July 2007
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Barrel - commissioning
EB-
Commissioning
The 36 Supermodules of the Barrel ECAL
have been fully integrated into the trigger
and readout chain of CMS
CMS ECAL
EB+
Presence of
the main
shaft
Top SMs
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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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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Barrel - commissioning
CMS ECAL
Energy
250 – 300 GeV
A cosmic ray event in CMS involving the
Barrel ECAL and Muon Drift Tubes
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A dramatic cosmic ray muon
bremstrahlung in the Barrel ECAL
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CMS Endcap ECAL
CMS ECAL
Supercrystal (SC)
25 crystals/VPTs
SC assy jig
EE crystals
SC assy jig
VPT HV cards
Cooling, electronics & optical readout mounted
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Supercrystal mounting
on a Dee backplate
A completed Dee with all Supercrystals
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CMS Endcap ECAL
CMS ECAL
Dee1 lowering and
rotation 19 July 08
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Dee1 mounting on HE
22 July 08
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Dee2 mounting on HE
24 July 08
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Preshower detector
CMS ECAL
Motivation: Improved 0/ discrimination
Rapidity 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
63mm
The first full Dee absorber with a
complete complement of sensors
Preshower installation expected during winter shutdown 2008/9
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Energy resolution
CMS ECAL
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
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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
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Resolution 0.44%
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Beam and Cosmic Muon pre-calibration
CMS ECAL
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: 4161 Cry:
168
Calibration coefficients from cosmic
muons versus those from the test
beam for 7 supermodules
Mip deposits ~250MeV
(increase APD gain from 50 to 200)
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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
CMS ECAL
Intercalibration precision at startup:
– Barrel ECAL
– Endcap ECAL
<2% (0.3% in ¼ of EB)
15%
0 resonance, Barrel ECAL
2006 test beam
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
(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mm
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CMS ECAL conclusions
CMS ECAL
• 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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CMS ECAL
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ECAL design objectives
CMS ECAL
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)
a stochastic term
Barrel
2.7%
End cap
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
Electronics,
pileup
low L 155 MeV
high L 210 MeV
770 MeV
915 MeV
A H    event in CMS with
MH=120GeV
Monte Carlo analyses: 5σ discovery potential for 115<MH<140GeV with 8 -16 fb-1
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Off-Detector electronics
CMS ECAL
TTC
TTS
mFEC
SLB
Trigger and Timing Card
Trigger Throttling System
mezzanine Front End Controller card
(connects to FE card via token ring)
Synchronisation and Link Board mezzanine
Clock & Control
System Card
(CCS)
Trigger
Concentrator
Card (TCC)
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Selective Readout
Processor (SRP)
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Data
Concentrator
Card (DCC)
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0
π
Calibration Concept
CMS ECAL
Data after L1 Trigger
0 Calibration
Online Farm
~1 kHz
>10 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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Calibration of CMS ECAL using π0γγ Decays
CMS ECAL
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 20 - 80 hours to calibrate 95% of barrel.
Exploit immediately after the startup!
First Resonance Observed
by CMS! (2006 Test beams)
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In-situ Calibration
CMS ECAL
Strategy at startup – Phi symmetry
Precision (%)
Rapid achievement of ~2% intercalibration
 symmetry of energy deposition ( intercalibration) in rings of
crystals
L1 triggers – single crystals, 1-6 GeV transverse energy (barrel)
4%
2%
Barrel
Eta
Endcap
Eta
Blue – after a few hours of data taking, luminosity 2.1033 cm-2s-2
Red - after ~ 1 day of data taking
Limit on precision due to tracker material etc
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Intercalibration from Laboratory
Measurements
CMS ECAL
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
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 = 4.2%
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