Speaker
Dr
Maria Margherita Obertino
(Universita' del Piemonte Orientale)
Description
The CMS ECAL is one of the highest resolution electromagnetic calorimeters ever constructed, but relies upon precision calibration in order to achieve and maintain its design performance. Variations in light collected from the lead tungstate crystals, due to intrinsic differences in crystals/photodetectors, as well as variations with time due to radiation damage for example, need to be taken into account. Sophisticated and effective methods of inter-crystal and absolute calibration have been devised, using collision data from the 2011 LHC run and a dedicated light injection system. For inter-calibration, low mass particle decays (pi0 and eta) to two photons are exploited, as well as the azimuthal symmetry of the average energy deposition at a given pseudorapidity. Absolute calibration has been performed using Z0 decays into electron-positron pairs. The light injection system monitors the transparency of the crystals in real-time and enables the re-calibration of the measured energies over time. This is cross-checked by the comparison of E/p measurements of electrons from W decays (where the momentum is measured in the CMS tracker) with/without these re-calibrations applied. The calibration procedures will be discussed in detail and we show the results obtained from the entire 2011 dataset.
for the collaboration
CMS
Primary author
Mr
Olivier Bondu
(IPN Lyon - UCB Lyon 1)
