Position resolution in crystal calorimeter

LYSO crystal, because of its major properties for instance, fast decay time, high light yield, small Molière radius and good radiation hardness, is proposed to be used for the electromagnetic calorimeter unit of Turkish Accelerator Center Particle Factory detector (TAC- PF ECAL). In this study, the center of gravity method was used to determine the position of the center of gravity of the electromagnetic shower initiated by an electron sent to a calorimeter consisting of a 3×3 LYSO matrix. The calorimeter consists of nine 200 mm long crystals, each with 25 mm × 25 mm front and backside faces. The performance of a calorimeter prototype consists of LYSO crystal scintillators has been measured at normal incidence by electron having energies between 0.1 GeV and 2 GeV. The position resolution of the TAC-PF electromagnetic calorimeter for an electron injected perpendicular to the central crystal is parameterized by means of GEANT4 Monte Carlo simulation as σ_x=(((2.77±0.07))⁄√E)⨁(1.46±0.10) mm in the x-axis direction, and σ_y=(((2.77±0.05))⁄√E)⨁(1.31±0.07) mm in the y-axis direction. Also, simulated position resolution in the two-dimensional prototype of ECAL is found to be σ_R=(((3.95±0.08))⁄√E)⨁(1.91±0.11) mm at the center of the central crystal. Finally, electrons are sent at various angles to the surface of the crystal matrix and the variation of position resolution depending on the electron incidence angle is investigated. It has been observed that the position resolution deteriorates as the incidence angle of the electron sent to the LYSO matrix increases and the best position resolution is obtained when the electron is sent perpendicular to the matrix surface.