Double side read-out technique for mitigation of radiation damage effects in PbWO₄crystals

Abstract

Test beam results of a calorimetric module based on 3×3×22 cm3 PbWO4 crystals, identical to those used in the CMS ECAL Endcaps, read out by a pair of photodetectors coupled to the two opposite sides (front and rear) of each crystal are presented. Nine crystals with different level of induced absorption, from 0 to 20 m−1, have been tested using electrons in the 50–200 GeV energy range. Photomultiplier tubes have been chosen as photodetectors to allow for a precise measurement of highly damaged crystals. The information provided by this double side read-out configuration allows to correct for event-by-event fluctuations of the longitudinal development of electromagnetic showers. By strongly mitigating the effect of non-uniform light collection efficiency induced by radiation damage, the double side read-out technique significantly improves the energy resolution with respect to a single side read-out configuration. The non-linearity of the response arising in damaged crystals is also corrected by a double side read-out configuration and the response linearity of irradiated crystals is restored. In high radiation environments at future colliders, as it will be the case for detectors operating during the High Luminosity phase of the Large Hadron Collider, defects can be created inside the scintillator volume leading to a non-uniform response of the calorimetric cell. The double side read-out technique presented in this study provides a valuable way to improve the performance of calorimeters based on scintillators whose active volumes are characterized by high aspect ratio cells similar to those used in this study.

Dual Cherenkov and Scintillation Response to High-Energy Electrons of Rare-Earth-Doped Silica Fibers

“…The energy resolution σ E /E of the reconstructed amplitude is found to decrease with increasing incident energy, thus following the expected trend [39]: at 200 GeV it is estimated to be around 15%, which mainly accounts for contributions from the partial transverse shower containment within a single fiber bundle and from the nonuniformity of the fibers themselves.…”

“…Nonuniformity along the fiber length in the efficiency of the light extraction at the fiber ends, if not corrected for (e g., by means of a double-sided readout [39]), can affect the response and the performance with high-energy particles. length of Ce-doped silica fibers was previously conducted with a 370-nm pulsed LED as the excitation source: the experimental procedure and results are described in Ref.…”

Predicting the Performance of the CMS Precision PbWO4 Electromagnetic Calorimeter in the HL-LHC Era From Test Beam Results on Irradiated Crystals

“…This permits a detailed examination of the mechanisms responsible for the degradation of signal linearity and energy resolution to electrons as well as the detailed validation of the simulation predictions, which are based on the modelling of light propagation inside the crystal volume [15].…”