Performance, Calibration
and Alignment of CMS
Preshower Detector
Rong-Shyang Lu
National Taiwan University
On behalf of CMS Collaboration
12th Topical Seminar on Innovative Particle and Radiation Detectors
(IPRD10) 7 - 10 June 2010 Siena, Italy
Outline
• Introduction
•
Why, what and where is Preshower
• Detector Performance with LHC beam
• Calibration and Alignment of Preshower
• Summary
IRPD10, Siena
Rong-Shyang Lu / NTU
June 8, 2010
2
Introduction
•
•
•
•
Preshower is designed as a
pre-sampling detector of
CMS Endcap Calorimeter
Measure “shower shape” in
front of Endcap crystal
calorimeter.
Identify single or multiple
photons
Physics requirement :
•
•
Energy resolution within 5%
Position resolution at submm for 60 GeV e/γ
IRPD10, Siena
Single incident photon
Two closely-spaced
incident photons
Low mass SM Higgs
But large reducible
decays to two isolated background from π0
faking single photon
photons
Rong-Shyang Lu / NTU
June 4, 2010
3
Preshower in CMS
•
2 layers of
•
•
•
lead absorbers (2X0, 1X0)
Silicon strip detectors +
front-end electronics
mechanical support and
service (cooling, power)
20cm
Preshower
(ES)
Barrel ECAL (EB)
2.5 m
y
η
.47
=1
653
.
1
η =
9
Preshower (ES)
η = 2.6
z
IRPD10, Siena
Endcap
ECAL (EE)
η : pseudo-rapidity = -ln(tan(θ/2))
Rong-Shyang Lu / NTU
η = 3.0
Endcap
ECAL (EE)
June 4, 2010
4
Preshower Detector
•
•
•
A detector module
Total of 4288 Silicon strip
detectors with custommade chips and hybrids
Detector thickness of
310μm with strip area of
1.9mm x 61mm and 32
strips per detector.
A ladder contains
7~10 modules
17m2 of detector surface
with detector strips
arranged in X-Y grid.
•
•
front plane, closer to IP,
has strip segmented in X
rear plane has strips
segmented in Y.
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Rong-Shyang Lu / NTU
June 4, 2010
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Front-end Readout Electronics
Signal Pulse Shape
Total of 137,216 channels
Amplified and shaped as
shown
Read out every 25ns (LHC
clock) for 3 samples (S1-3)
Digitized by 12-bit ADCs
Two switchable gains
•
•
High Gain : with S/N~10
for a MIP for calibration and
LHC low energy run
Low Gain : with S/N~3 for a
MIP, for high luminosity LHC
run
S3
S1
Number of sensors
•
•
•
•
•
S2
MIP S/N in
collision data.
Agree with
expectation
250 CMS Preliminary 2010
s = 7 TeV
200
150
100
50
MIP : an approximate term for a charged
00
hadron or muon leaving dE/dx on silicon
Rong-Shyang Lu / NTU
IRPD10, Siena
2
4
6
8
10
12
14
16
18
20
Signal-to-Noise
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Detector Performance
Detector Commissioning
The noise performance agrees with earlier test beam
results and meets with requirement
Strips
•
Detector is installed on Apr. 2009
More than 99.8% of channels functioning.
(64 strips are not biased and around 100 channels have
intrinsic noise > 15 ADC in high gain. Therefore, they are
masked in readout)
105
High Gain
104
1 MIP : ~50 ADC
Strips
•
•
105
103
103
102
102
10
10
1
0
2
4
6
8
10 12 14 16 18 20
Intrinsic noise per strip (ADC counts)
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Low Gain
104
1
0
1 MIP : ~9 ADC
2
4
6
8
10 12 14 16 18 20
Intrinsic noise per strip (ADC counts)
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Performance - Beam Splash 2009
•
•
Average flux is about 5 muons/cm2 for the event
•
•
consistent with other detectors
Isolated hot spots due to muon bremsstrahlung
First time seeing LHC beams. Data used to tune ES timing
/sensor
•
Beam was deliberately dumped on collimators 150m upstream of
CMS producing secondary particles
Muons
Muons
EB/EE
(in red)
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Preshower (in green)
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Performance - LHC Collisions
•
Observing clusters linked between
Preshower and EE
•
•
•
Start from EE clusters with significant
energy deposit
Extrapolate back to IP and find the
intercept points on Preshower planes
Look for preshower signal in the
search window
Barrel ECAL (EB)
y
η
9
.47
1
=
η
z
η
653
.
1
=
Preshower (ES)
= 2.6
η
= 3.0
η : pseudo-rapidity = -ln(tan(θ/2))
IRPD10, Siena
EE cluster
Rong-Shyang Lu / NTU
Endcap
ECAL (EE)
Preshower
search window
June 4, 2010
10
Performance - LHC Collisions
•
Observed clusters linked
between Preshower and EE
3 EE clusters found in an
example event
Linked ES clusters were found
on both planes.
•
•
1
2
1
2
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3
1
3
Rong-Shyang Lu / NTU
2
3
June 4, 2010
11
Energy deposits in Preshower planes show consistent
results as expected.
•
More energy deposits in rear plane due to the more
material in front.
3
CMS Preliminary 2010
s = 7 TeV
60
Data
50
MC
40
front plane
30
20
10
0
20
40
60
80 100 120 140
ES Clus 1(X)
E
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(MIPs)
70
! 10
3
3
CMS Preliminary 2010
s = 7 TeV
60
Data
50
MC
40
rear plane
30
20
10
0
20
40
60
80 100 120 140
ES Clus 2(Y)
E
(MIPs)
Rong-Shyang Lu / NTU
of ES clusters
Num. Number
of superclusters
/ 0.25
70
! 10
•
of ES /clusters
Num. ofNumber
superclusters
5 MIPs
Num. of Number
superclusters
5 MIPs
of ES /clusters
Performance - LHC Collisions
40 !10
CMS Preliminary 2010
35
s = 7 TeV
30
Data
25
MC
rear / front plane
20
15
10
5
0
1
2
3
4
5
6
ES Clus 2(Y)
E
7
8
ES Clus 1(X)
/E
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12
Occupancy in Collision events
•
•
•
The occupancy is defined as number of strips with energy
greater than 4 times the noise
Occupancy increases as function of η and collision energy.
Expect to have a few % of occupancy at high η with 14TeV
and 1034 LHC luminosity
Occupancy (%)
0.5
CMS Preliminary 2010
0.45
s = 900 GeV
0.4
s = 2.36 TeV
0.35
s = 7 TeV
0.3
0.25
0.2
0.15
0.1
0.05
0 1.6
1.8
2
2.2
√s = center of mass energy of LHC collisions
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2.4
2.6
|!|
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Calibration and
Alignment
Energy Pre-Calibration
•
•
•
•
All sensors went through burn-in,
thermal cycles and cosmic-ray precalibration
Pre-calibration using MIPs with
correction applied on sensor
thickness, temperature, and
crossing angle.
Accuracy at 2.5% with 24 hours of
data taking.
Energy deposit
on Preshower
in Cosmic data
5% of resolution is needed.
Pulse shape from Cosmic data
IRPD10, Siena
Rong-Shyang Lu / NTU
MIP (ADC count)
June 4, 2010
15
•
90
80
70
60
CMS Preliminary 2010
s = 7 TeV
MIP = 45.1± 0.4
50
40
30
20
10
00
20
40
60
80
100
120
140
Reconstructed hit energy (ADC counts)
65
60
CMS Preliminary 2010
s = 7 TeV
120
100
55
80
50
60
45
40
40
20
3535
40
45
50
55
60
65
Number of sensor
•
In-situ calibration looks at
the energy deposit from
charged hadrons passing
through Preshower.
Results from first in-situ
calibration is within 3.3% of
pre-calibration value.
5 % of energy resolution is
needed
MIP from Collision (ADC)
•
Number of reco. hits
In-situ Energy Calibration
0
MIP from Cosmic Ray (ADC)
IRPD10, Siena
Rong-Shyang Lu / NTU
June 4, 2010
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Alignment with EE
•
•
•
•
Look for Preshower (ES) signal in front of EE cluster
Event display shows correlation between EE and ES clusters.
Residual distribution shows alignment better than 2mm.
With early data and lack of high energy e/γ, the width is
dominated by low energy particles. Will decrease to less than
1mm with high energy electrons/photons.
10
5
CMS Preliminary 2009
s = 900 GeV
EE Basic Cluster
E 7.0 GeV
" 2.4; ! 0.1
X 59.3; Y 4.6
1 ES X cluster
3 ES Y cluster
Combine (ESX1, EXSY1)
0
E1
Entries / 0.2cm
Y (cm)
3
!10
CMS Preliminary 2010
s = 7 TeV
2
1.5
E1
E2
E3
1
ES+
front
ES+F
data on 1(X)
data on 2(Y)
MC dist.
Width is not
resolution
-5
0.5
-10
-10
-5
0
5
10
0
-10
X (cm)
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-5
0
5
10
residual (cm)
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17
Alignment w.r.t. Tracker
•
Extrapolate track
trajectory from Tracker to
Preshower.
•
Select high purity track
and match with
Preshower signal
•
Minimizing residuals
between track trajectory
and Preshower hits while
floating Preshower in 3-D
space.
IRPD10, Siena
Ecal Endcap
Preshower
ECAL Barrel
Tracker
A Simulation event showing inner geometry
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June 4, 2010
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•
•
After alignment, residual
is narrower with mean
at zero ± 70μm
A few mm misalignment
can be accounted by
software
IRPD10, Siena
Entries
Aligned
ES+F
CMS Preliminary 2010
s = 7 TeV
Mean
0.002
Width
0.261
3000
Aligned
ES-F
CMS Preliminary 2010
s = 7 TeV
Mean
0.005
Width
0.263
2000
un-Aligned
Mean
0.498
Width
0.308
un-Aligned
2000
Mean
-0.022
Width
0.317
1000
1000
0
-3
-2
-1
0
1
2
0
-3
3
-2
-1
0
X-Residual (cm)
4000
Aligned
ES+R
CMS Preliminary 2010
s = 7 TeV
Mean
-0.000
Width
0.261
2000
1
-0.793
Width
0.333
3
Aligned
ES-R
CMS Preliminary 2010
s = 7 TeV
un-Aligned
Mean
2
X-Residual (cm)
Entries
•
Consistent alignment
constants between 2
planes in same endcap.
Plots show only the
measurement with
good resolution in X or
Y for each plane.
Entries
•
Entries
Alignment Results
Mean
-0.007
Width
0.242
un-Aligned
2000
Mean
-0.807
Width
0.331
1000
0
-3
-2
-1
0
Rong-Shyang Lu / NTU
1
2
3
Y-Residual (cm)
0
-3
-2
-1
0
1
2
3
Y-Residual (cm)
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19
•
•
Inefficiency due to fake
track, fake ES signal or
multiple scattering.
Agree with prediction
from simulation.
1.04
1.02
1
CMS Preliminary 2010
s = 7 TeV
Data
MC
0.98
0.96
0.94
0.92
0.9
data/MC
•
Measure the matching
efficiency between track
trajectory and Preshower
measurement.
Efficiency
Preshower-Tracker matching efficiency
1.04
1.02
1
0.98
0.96
2
4
6
8
10
Track p (GeV/c)
T
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Summary
•
CMS ECAL-Preshower detector has been
commissioned and fully operational taking LHC
collision data.
•
The performance agrees with expectation from
earlier test beam studies and Monte-Carlo
simulation matching with requirement.
•
The calibration and alignment procedures were
performed.
•
•
First in-situ calibration achieves required accuracy
Alignment with EE and Tracker improves the position
measurements.
IRPD10, Siena
Rong-Shyang Lu / NTU
June 8, 2010
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Backup Slide
Preshower
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Preshower Timing
• The Timing of Preshower was adjusted
Number of Ladders
using cosmic-ray, beam-splash and later by
Collision data.
120
CMS Preliminary 2010
100
Calibrated Time
Mean : 0.0, RMS : 0.3 (ns)
80
Uncalibrated Time
Mean : 1.4, RMS : 2.8 (ns)
60
40
20
0
-8
-6
-4
-2
0
2
4
6
8
Ladder Mean Timing (ns)
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Energy resolution - beam test
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Spatial Resolution - beam test
Front plane
0 degree incident angle
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rear plane
0 degree incident angle
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26