Jelena Mijušković

Abstract The electromagnetic calorimeter (ECAL) of the CMS detector has played an important role in the physics program of the experiment, delivering outstanding performance throughout data taking. The high-luminosity LHC will pose new challenges. The four to five-fold increase of the number of interactions per bunch crossing will require superior time resolution and noise rejection capabilities. For these reasons the electronics readout has been completely redesigned. A dual gain trans-impedance amplifier and an ASIC providing two 160 MHz ADC channels, gain selection, and data compression will be used in the new readout electronics. The trigger decision will be moved off-detector and will be performed by powerful and flexible FPGA processors, allowing for more sophisticated trigger algorithms to be applied. The upgraded ECAL will be capable of high-precision energy measurements throughout HL-LHC and will greatly improve the time resolution for photons and electrons above 10 GeV.

Three NaI(Tl) detectors and two pairs of NaI(Tl) detectors at an angle of 90 -from the six-crystal spectrometer PRIPJAT-2M (Faculty of Natural Sciences and Mathematics, University of Montenegro, Podgorica), were used to determine registration efficiencies for the most intense gamma rays in de-excitation of 134 Ba, following beta minus decay of 134 Cs.The 134 Cs liquid calibration standard was used for acquiring spectra over 18 000 s real time in the energy range (200-3000) keV -in the integral, non-coincident and mode of double gamma-gamma coincidences.All the spectra from individual detectors and detector pairs in all the counting modes clearly showed peaks at the 605 and 796 keV.The experimental registration efficiency of the 605 keV gamma ray by individual detectors in different modes of counting was found to be with an average of 0.055 (integral), 0.032 (non-coincident) and 0.021 (double coincidences), whilst in the case of two detector pairs -0.112 (integral), 0.065 (non-coincident) and 0.042 (double coincidences).In regards to the 796 keV, average detection efficiencies were 0.04 (integral), 0.026 (non-coincident) and 0.013 (double coincidences) -in the case of individual detectors, and 0.076 (integral), 0.048 (non-coincident) and 0.026 (double coincidences) -for the detector pairs.Obtained results are baselines for the future development of the coincidence method for 134 Cs measurement -using multidetector systems with measuring geometry close to 4π, with the 796 keV photopeak in a coincidence mode as appropriate for 134 Cs detection in a sample containing 137 Cs and decay products of 226 Ra and 232 Th.