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Testbeam results of the CMS electromagnetic calorimeter Alessio Ghezzi on behalf of CMS ECAL Collaboration
Outline • Energy reconstruction technique and performances • Impact point reconstruction • Intercalibration • Irradiation monitoring performances • Cooling system
Hodoscopes Beam Movable Table Supermodule 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
2003: 2 test periods SM0SM1 # gains 4 3 SM (# equip. crys.) FPPA (100 chan.) MGPA (50 chan.) period long 1.5 months short 10 days Electron energies(GeV)20, 35, 50, 80, 120, 150, 180, 200 25, 50, 70, 100 Test beams data • 2002 : 100 channels with “old” electronic (FPPA) detailed study of: • Laser monitoring • intercalibration • cooling system
Amplitude SM0/FPPA Tpeak Tmax Time (*25 ns) Energy reconstruction 3 pedestal samples and 11 signal samples 40 MHz Wi determined minimizing Under the constraints
Pedestal run Sum over 3x3 matrix s: 129 MeV Amplitude (MeV) Energy resolution Electrons incident on a 4x4 mm2 central region Noise term determined from pedestal runs sE/E (%) Ebeam (GeV)
Deposited energy Two methods: • • Position reconstruction Impact point reconstructed by hodoscopes (s ~ 150 mm) Measure impact position from calorimetric information Xi: position of the i-th crystal
Position reconstruction S curve is E,h,F dependent Resolution varies with impact position (better resolution close to crystal edges) Y (reco.–true) mm Y (reco.–true) mm Logarithmic weights 1mm =700m G. Daskalakis I. Van Vulpen Y (reco.–true) mm
M Intercalibration Procedure • Cancel out the dependence of reconstructed energy on impact position by equalizing to the maximum response: IV order polynomial fit selections: e- impacting within a 7 x 7 mm2 central region ( retains ~25% of events ) Channel response: position of peak M, fitted by a Gaussian + exp left tail Relative calibration:
RMS :~0.3% ~1000 triggered events RMS:~0.09% Dintercalib. Dintercalib. Intercalibration Statistical accuracy: compare the intercalibration obtained using only a reduced sample of data w.r.t. to the one with the whole statistic Comparison of intercalibration from different data set Same accuracy as 2002 results An accuracy of ~ 0.1% can be achieved with 1000 triggered events
M s = 4.05% Containment: ~0.8 @ 120 GeV Electronic gain APD Gain F. Cavallari 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
a a = 1.55 a Electron signal ~5% Laser signal Irradiation Monitoring Irradiation affects only the light transmission Monitoring and correct for the loss in response by the injection of laser light as reference A. Van Lysebetten P. Verrecchia
s/m = 6.3% a Irradiation Monitoring 2002 and 2003 data: it is possible to use the same a for all the crystal PRELIMINARY 2002 A. Van Lysebetten P. Verrecchia signal amplitude (ADC counts) After the correction for loss in transparency Time (hours)
Thermal step The APD gain (M) depends on the temperature : Also the LY depends on the temperature The two effects sum up in the overall response (R): a and b measured in a thermal step aT = - 2.44 % / °C Laser runs Electrons runs Average thermistor temperature 1 ºC bT = - 4.1 % / °C
0.1 C 7 days Cooling system Cooling bars PRELIMINARY 1 C PRELIMINARY Cooling system with cooling bar ~1.5 month
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
pure signal A f(t) Energy reconstruction
Spread in Time of maximum response Resolution versus mismatch SM0/FPPA (E)/E (%) Number of events 25 ns Normalised Tmax Tmax mismatch (ns) Energy reconstruction E resolution VS # of pulse samples SM0/FPPA (E)/E (%)
Position reconstruction uncorrected S-curve corrected S-curve Y (reco.–true) mm E = 120 GeV Reconstructed (Y) mm =620m Resolution versus impact position Y (reco.–true) mm Best resolution: close to crystal edge Worst resolution: max. energy fraction in central crystal
Laboratory measurements Precalibration starting from LY measurements in laboratory : 60Co source 1.2 MeV
0.5 % Test beam 2002 LY LY D intercalibration coeff.
6 days average thermistors temperature 2002 0.06 ºC 2 months Test beam 2002 Cooling Uniformity of temperature within a module 0.04 ºC Stability over a long period