Beam test evaluation of electromagnetic calorimeter modules made from proton-damaged PbWO_4 crystals
The performance of electromagnetic calorimeter modules made of proton-irradiated PbWO_4 crystals has been studied in beam tests. The modules, similar to those used in the Endcaps of the CMS electromagnetic calorimeter (ECAL), were formed from 5×5 matrices of PbWO_4 crystals, which had previously been exposed to 24 GeV protons up to integrated fluences between 2.1× 10^(13) and 1.3× 10^(14) cm^(−2). These correspond to the predicted charged-hadron fluences in the ECAL Endcaps at pseudorapidity η = 2.6 after about 500 fb^(−1) and 3000 fb^(−1) respectively, corresponding to the end of the LHC and High Luminosity LHC operation periods. The irradiated crystals have a lower light transmission for wavelengths corresponding to the scintillation light, and a correspondingly reduced light output. A comparison with four crystals irradiated in situ in CMS showed no significant rate dependence of hadron-induced damage. A degradation of the energy resolution and a non-linear response to electron showers are observed in damaged crystals. Direct measurements of the light output from the crystals show the amplitude decreasing and pulse becoming faster as the fluence increases. The latter is interpreted, through comparison with simulation, as a side-effect of the degradation in light transmission. The experimental results obtained can be used to estimate the long term performance of the CMS ECAL.
Additional Information© 2016 CERN published under the terms of the Creative Commons Attribution 3.0 License by IOP Publishing Ltd and Sissa Medialab srl. Any further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation and DOI. Received 25 January 2016. Accepted 21 March 2016. Published 11 April 2016. We would like to acknowledge our colleagues of the CERN SPS facility and all engineers and technicians whose work on the preparation of the test beam modules, their operation and data-taking, made these results possible. We also thank Maurice Glaser and Federico Ravotti who have been responsible for the proton irradiation at the CERN PS IRRAD facility. We are also grateful to the CMS Technical Coordination team who helped setting up the crystal exposure inside the CMS cavern.
Published - jinst16_04_p04012.pdf