Testbeam results of the CMS electromagnetic
calorimeter
Alessio Ghezzi
on behalf of CMS ECAL Collaboration
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
1
Outline
• Energy reconstruction technique and performances
• Impact point reconstruction
• Intercalibration
• Irradiation monitoring performances
• Cooling system
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
2
Experimental setup
Laser monitoring system and HV system
(for APDS) : final scheme
LV system : prototype
cooling system: final prototype
•moving table
•plastic scintillator for trigger
•Hodoscopes (s~145 mm)
•Laser monitoring system
Hodoscopes
Beam
INFN Milano,
Universita` degli Studi Milano Bicocca
Movable
Table
Siena IPRD04
23-26 May 2004
Supermodule
3
Test beams data
2002 : 100 channels with “old” electronic (FPPA) detailed study of:
• Laser monitoring
• intercalibration
• cooling system
2003: 2 test periods
SM0
# gains
SM1
4
SM (# equip. crys.)
period
3
FPPA (100 chan.)
long
1.5 months
MGPA (50 chan.)
short 10 days
Electron energies (GeV) 20, 35, 50, 80, 120, 150, 180, 200
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
25, 50, 70, 100
4
Energy reconstruction
3 pedestal samples and 11 signal samples 40 MHz
n
A   Si  wi
Amplitude
i 1
Wi determined minimizing
 2  ( S  A  F  P)T Cov 1 ( S  A  F  P)

Under the constraints
 wi  0
w  f
i
i
 t 
f (t )  

 Tpeak 

1
e
f i  f (ti )
Tpea
k
INFN Milano,
Tmax
Universita` degli Studi Milano Bicocca
SM0/FPPA
Siena IPRD04
Time
23-26(*25
Mayns)
2004
5
 t -Tpeak
- 
 Tpeak



Energy resolution
sE
a
b

 c
E
E E
Electrons incident on a 4x4 mm2 central region
sE
E

(2.9  0.2)% (129  2 ) MeV

 (0.4  0.03)%
E
E / GeV
Pedestal run
Sum over
3x3 matrix
s: 129 MeV
Amplitude (MeV)
INFN Milano,
Universita` degli Studi Milano Bicocca
sE/E (%)
Noise term determined from pedestal runs
Ebeam (GeV)
Siena IPRD04
23-26 May 2004
6
Position reconstruction
Impact point reconstructed by hodoscopes (s ~ 150 mm)
Deposited
energy
Measure impact position
from calorimetric
information
x
Two methods:
w x


w
i
i
i
i
i
Xi: position of the i-th crystal
INFN Milano,
Universita` degli Studi Milano Bicocca
•
wi  Ei
 Ei 
• wi  w0  log   Ej  wi  0
 j 
Siena IPRD04
23-26 May 2004
7
Y (reco.–true) mm
Position reconstruction
wi  Ei
S curve is E,h,F dependent
Resolution varies with impact
position (better resolution
close to crystal edges)
Y (reco.–true) mm
Logarithmic weights
s Y (mm) 
1mm
s=700mm
Y (reco.–true) mm
INFN Milano,
Universita` degli Studi Milano Bicocca
G. Daskalakis
I. Van Vulpen
Siena IPRD04
23-26 May 2004
8
5040
 430
E / GeV
Intercalibration Procedure
• Cancel out the dependence of
reconstructed energy on impact
position by equalizing to the maximum
response: IV order polynomial fit
Channel response:
position of peak M,
fitted by a Gaussian
+ exp left tail
selections: e- impacting within a 7 x 7 mm2
central region ( retains ~25% of events )
Relative calibration:
Mi
i 
M Ref
INFN Milano,
Universita` degli Studi Milano Bicocca
M
Siena IPRD04
23-26 May 2004
9
Intercalibration
Comparison of intercalibration
from different data set
Statistical accuracy: compare
the intercalibration obtained using
only a reduced sample of data w.r.t. to
the one with the whole statistic
RMS :~0.3%
~1000 triggered
events
RMS:~0.09%
intercalib.
Same accuracy as 2002 results
intercalib.
An accuracy of ~ 0.1% can be achieved
with 1000 triggered events
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
10
Intercalibration from
laboratory measurements
Only few modules will be calibrated on a beam
Precalibration starting from Light Yield
measurements in laboratory : 60Co source 1.2 MeV
M
LYTestBeam 
 cont
Containment:
~0.8 @ 120 GeV
Signal
Ebeam M APD Ael
s = 4.05%
Electronic gain
APD Gain
F. Cavallari
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
11
Irradiation Monitoring
Irradiation affects only the light transmission
Monitoring and correct for the loss in
response by the injection of laser light as
reference
Electron signal

 = 1.55

~5%

S  R
 
S0  R0 
INFN Milano,
Universita` degli Studi Milano Bicocca
A. Van Lysebetten
P. Verrecchia
Laser signal
Siena IPRD04
23-26 May 2004
12
Irradiation Monitoring
s/m = 6.3%
2002
A. Van Lysebetten
P. Verrecchia

After the correction for loss
in transparency
signal amplitude (ADC counts)
2002 and 2003 data: it is possible to
use the same  for all the crystal
PRELIMINARY
Time (hours)
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
13
Thermal step
The APD gain (M) depends on the temperature :
Also the LY depends on the temperature
T (% / 0C ) 
The two effects sum up in the overall response (R):
1 dM
M dT
bT (% / 0C ) 
 and b measured in a thermal step
Laser runs
Electrons runs
1 dR
R dT
T = - 2.44 % / °C
Average thermistor temperature
1 ºC
bT = - 4.1 % / °C
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
14
Cooling system
Cooling bars
PRELIMINARY
0.1 C
7 days
PRELIMINARY
1 C
Cooling system with cooling bar
~1.5 month
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
15
Summary
• The new Very Front End cards equipped with MGPA satisfy the target
specifications .
• The impact point reconstruction shows a resolution better than 1mm for
Energy > 35 GeV
• A robust intercalibration procedure on e- beam has been developed, and
an initial intercalibration at ~4% level is reachable for all the crystals
from laboratory measurements of the light yield
• The laser monitoring system and the cooling system satisfy the
performances required for CMS
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
16
Back up
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
17
Energy reconstruction
pure signal
A
f(t)
n
A   Si  wi
i 1
w  0
i
wi   fi  
  i ( fi ) 


fi

n i
1
2
 f / n
2
i
i

 t 
f (t )  

 Tpeak 
INFN Milano,
Universita` degli Studi Milano Bicocca
e
 t -Tpeak
- 
 Tpeak



Siena IPRD04
23-26 May 2004
fi
wi 
2
(
f
i
i )
18
Energy reconstruction
SM0/FPPA
Number of events
Spread in Time of
maximum response
SM0/FPPA
s(E)/E
(%)
Resolution versus mismatch
s(E)/E
(%)
E resolution VS
# of pulse samples
25 ns
Tmax mismatch (ns)
Normalised Tmax
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
19
Y (reco.–true) mm
Position reconstruction
uncorrected S-curve
corrected S-curve
E = 120 GeV
wi  Ei
Reconstructed (Y) mm
Best resolution:
close to crystal edge
Resolution
versus impact
position
s=620mm
Y (reco.–true) mm
Worst resolution: max. energy fraction in central crystal
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
20
Laboratory measurements
Precalibration starting from LY measurements in
laboratory : 60Co source 1.2 MeV
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
21
Test beam 2002 LY
0.5 %
 intercalibration coeff.
INFN Milano,
Universita` degli Studi Milano Bicocca
LY
Siena IPRD04
23-26 May 2004
22
Test beam 2002 Cooling
average thermistors temperature
Uniformity of temperature
within a module
2002
6 days
0.06 ºC
2 months
0.04 ºC
Stability over a long period
INFN Milano,
Universita` degli Studi Milano Bicocca
Siena IPRD04
23-26 May 2004
23