Precision timing measurements for high energy photons

Abstract

Particle colliders operating at high luminosities present challenging environments for high energy physics event reconstruction and analysis. We discuss how timing information, with a precision on the order of 10ps, can aid in the reconstruction of physics events under such conditions. We present calorimeter based timing measurements from test beam experiments in which we explore the ultimate timing precision achievable for high energy photons or electrons of 10GeV and above. Using a prototype calorimeter consisting of a 1.7×1.7×1.7cm3 lutetium–yttrium oxyortho-silicate (LYSO) crystal cube, read out by micro-channel plate photomultipliers, we demonstrate a time resolution of 33.5±2.1ps for an incoming beam energy of 32GeV. In a second measurement, using a 2.5×2.5×20cm3 LYSO crystal placed perpendicularly to the electron beam, we achieve a time resolution of 59±11ps using a beam energy of 4GeV. We also present timing measurements made using a shashlik-style calorimeter cell made of LYSO and tungsten plates, and demonstrate that the apparatus achieves a time resolution of 54±5ps for an incoming beam energy of 32GeV.