STUDY OF $\mathrm{PbWO}_4$ CRYSTAL FOR ePIC EmCal PROTOTYPE

Abstract

The study presents the characterization of $\mathrm{PbWO}_4$ crystals intended for the prototype of the EmCal electromagnetic calorimeter of the ePIC detector, which is being constructed at the Electron-Ion Collider in the Brookhaven National Laboratory at the USA.  Measurements were performed on 20 crystals produced by "Crytur" company, each of which was then thoroughly examined under a microscope. Transversal transparency measurements were made at the center of the crystals, as well as at several fixed points equidistant from the center to the right and left sides to study uniformity. The average transparency of the crystals is 21.3%, 65.6%, and 71.7% for wavelengths of 360 nm, 440 nm, and 600 nm, respectively. The transmittance measurements repeated 10 times in the center of each crystal show that accuracy of our measurement is better than 10%. The light yield of $\mathrm{PbWO}_4$  was estimated to be an average 16 pe/MeV. The optical characteristics of Crytur crystals meet the requirements of the EIC electromagnetic calorimeter. After performing all the necessary measurements, 16 crystals in good condition were selected for the calorimeter prototype. A 4$\times$4 prototype of EmCal was designed, constructed and tested with cosmic muons.