INFN Milano,Universita` degli Studi Milano Bicocca 1
Siena IPRD0423-26 May 2004
Testbeam results of the CMS electromagnetic calorimeter
Alessio Ghezzi
on behalf of CMS ECAL Collaboration
INFN Milano,Universita` degli Studi Milano Bicocca 2
Siena IPRD0423-26 May 2004
Outline
• Energy reconstruction technique and performances
• Impact point reconstruction
• Intercalibration
• Irradiation monitoring performances
• Cooling system
INFN Milano,Universita` degli Studi Milano Bicocca 3
Siena IPRD0423-26 May 2004
Experimental setup
SupermoduleMovable Table
Beam
Hodoscopes
Laser monitoring system and HV system(for APDS) : final scheme LV system : prototype cooling system: final prototype
•moving table•plastic scintillator for trigger•Hodoscopes (~145 m)•Laser monitoring system
INFN Milano,Universita` degli Studi Milano Bicocca 4
Siena IPRD0423-26 May 2004
Test beams data
2002 : 100 channels with “old” electronic (FPPA) detailed study of:• Laser monitoring • intercalibration • cooling system
2003: 2 test periods
Electron energies (GeV) 20, 35, 50, 80, 120, 150, 180, 200 25, 50, 70, 100
SM (# equip. crys.) FPPA (100 chan.) MGPA (50 chan.)
SM0 SM1
# gains 4 3
period long 1.5 months short 10 days
INFN Milano,Universita` degli Studi Milano Bicocca 5
Siena IPRD0423-26 May 2004
Energy reconstruction
3 pedestal samples and 11 signal samples 40 MHz
Amplitude 1
n
i ii
A S w
Tmax
Tpea
k Time (*25 ns)
SM0/FPPA
0iw Under the constraints
Wi determined minimizing
peak
peak
-T-
T
peak( ) e
T
tt
f t
2 1( ) TS A F P Cov ( S A F P)
1i iw f )( ii tff
INFN Milano,Universita` degli Studi Milano Bicocca 6
Siena IPRD0423-26 May 2004
Energy resolution
E a bc
E EE
Electrons incident on a 4x4 mm2 central region
Pedestal run
Amplitude (MeV)
: 129 MeVSum over 3x3 matrix
Noise term determined from pedestal runs
E/E
(%
)
Ebeam (GeV)
)%03.04.0() 2129(
/
)%2.09.2(
E
MeV
GeVEEE
INFN Milano,Universita` degli Studi Milano Bicocca 7
Siena IPRD0423-26 May 2004
Position reconstruction
Deposited energy
Impact point reconstructed by hodoscopes ( ~ 150 m)
Measure impact position from calorimetric information
ii
iii
w
xwx
Xi: position of the i-th crystal
Two methods:
0 log 0 i
i ij
j
Ew w w
E
i iw E
•
•
INFN Milano,Universita` degli Studi Milano Bicocca 8
Siena IPRD0423-26 May 2004
Position reconstruction
Y (
reco
.–tr
ue)
m
m
ii Ew S curve is E,dependent
Resolution varies with impact position (better resolution close to crystal edges)
=700m
Y (reco.–true) mm
Y (reco.–true) mm
Logarithmic weights
G. DaskalakisI. Van Vulpen
430/
5040)
GeVEm(Y
1mm
INFN Milano,Universita` degli Studi Milano Bicocca 9
Siena IPRD0423-26 May 2004
Intercalibration Procedure
selections: e- impacting within a 7 x 7 mm2 central region ( retains ~25% of events )
• Cancel out the dependence of reconstructed energy on impact position by equalizing to the maximum response: IV order
polynomial fit
MRef
ii
M
M Relative calibration:
Channel response:position of peak M, fitted by a Gaussian+ exp left tail
INFN Milano,Universita` degli Studi Milano Bicocca 10
Siena IPRD0423-26 May 2004
Intercalibration
Comparison of intercalibration from different data set
Same accuracy as 2002 results
Statistical accuracy: comparethe intercalibration obtained using only a reduced sample of data w.r.t. tothe one with the whole statistic
An accuracy of ~ 0.1% can be achievedwith 1000 triggered events
RMS :~0.3%
intercalib.
~1000 triggered events
RMS:~0.09%
intercalib.
INFN Milano,Universita` degli Studi Milano Bicocca 11
Siena IPRD0423-26 May 2004
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
cont beam APD elTestBeam
Signal
E MLY
A
Containment:~0.8 @ 120 GeV
APD Gain
Electronic gain
M
= 4.05%
F. Cavallari
INFN Milano,Universita` degli Studi Milano Bicocca 12
Siena IPRD0423-26 May 2004
Irradiation Monitoring
Laser signal
Ele
ctro
n s
ign
al
= 1.55
0 0
S
S
R
R
~5%
Irradiation affects only the light transmission
Monitoring and correct for the loss in response by the injection of laser light as reference
A. Van LysebettenP. Verrecchia
INFN Milano,Universita` degli Studi Milano Bicocca 13
Siena IPRD0423-26 May 2004
Irradiation Monitoring
// = 6.3% = 6.3%// = 6.3% = 6.3%
2002 and 2003 data: it is possible to use the same for all the crystal
After the correction for loss
in transparency
2002A. Van LysebettenP. Verrecchia
Time (hours)
sign
al a
mpl
itud
e (A
DC
cou
nts) PRELIMINARY
INFN Milano,Universita` degli Studi Milano Bicocca 14
Siena IPRD0423-26 May 2004
Thermal step
0 1 (% / )T
dMC
M dT The APD gain (M) depends on the temperature :
Also the LY depends on the temperature
Average thermistor temperature
T = - 4.1 % / °C
The two effects sum up in the overall response (R): 0 1 (% / )T
dRC
R dT
and measured in a thermal step
Laser runs Electrons runs T = - 2.44 % / °C
1 ºC
INFN Milano,Universita` degli Studi Milano Bicocca 15
Siena IPRD0423-26 May 2004
Cooling system
1 C
0.1 C
7 days
Cooling system with cooling bar
~1.5 month
Cooling bars
PRELIMINARY
PRELIMINARY
INFN Milano,Universita` degli Studi Milano Bicocca 16
Siena IPRD0423-26 May 2004
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 17
Siena IPRD0423-26 May 2004
Back up
INFN Milano,Universita` degli Studi Milano Bicocca 18
Siena IPRD0423-26 May 2004
Energy reconstruction
peak
peak
-T-
T
peak( ) e
T
tt
f t
i iw f
1
n
i ii
A S w
/)(221 nff
ii
ii
0iw
i
ifn
A
pure signal
f(t)
ii
ii
f
fw
)( 2
INFN Milano,Universita` degli Studi Milano Bicocca 19
Siena IPRD0423-26 May 2004
Energy reconstruction
(E)/
E
(%)
SM0/FPPA
E resolution VS # of pulse samples
Normalised Tmax
25 ns
Num
ber
of
events
Spread in Time of maximum response
Resolution versus mismatch
Tmax mismatch (ns)
(E)/
E
(%)
SM0/FPPA
INFN Milano,Universita` degli Studi Milano Bicocca 20
Siena IPRD0423-26 May 2004
Position reconstruction
=620m
ii Ew Y (
reco
.–tr
ue)
mm uncorrected S-curve
Worst resolution: max. energy fraction in central crystal
Best resolution:
corrected S-curve
Reconstructed (Y) mm
close to crystal edge
Resolution versus impact position Y (reco.–true) mm
E = 120 GeV
INFN Milano,Universita` degli Studi Milano Bicocca 21
Siena IPRD0423-26 May 2004
Laboratory measurements
Precalibration starting from LY measurements in laboratory : 60Co source 1.2 MeV
INFN Milano,Universita` degli Studi Milano Bicocca 22
Siena IPRD0423-26 May 2004
Test beam 2002 LY
0.5 %
LY intercalibration coeff.
INFN Milano,Universita` degli Studi Milano Bicocca 23
Siena IPRD0423-26 May 2004
Test beam 2002 Cooling
average thermistors temperature
2 months
0.06 ºC
2002
Stability over a long period
Uniformity of temperaturewithin a module
6 days
0.04 ºC