Characterization of a 5 <tex-math notation='LaTeX'>$5 \times 5$</tex-math> LYSO Matrix Calorimeter Prototype

In this paper, we present measurements of the energy and the time resolution of the Lutetium–Yttrium Oxyorthosilicate (LYSO) calorimeter prototype for the Mu2e experiment. The prototype calorimeter matrix consisted of 25, $\hbox{3}\,\hbox{$\times$}\, \hbox{3}\,\hbox{$\times$}\, \hbox{130\ mm}^3$ , LYSO crystals readout by $10\ \times 10\ \hbox{mm}^2$ Hamamatsu APDs. The prototype has been tested both with the tagged photon beam at MAMI, Mainz, Germany, and with the ${e^ -}$ beam of BTF, Frascati. The energy of particles used ranges between 61.3 and 187.1 MeV (80–130 MeV) for photon (electron) beams. While the MAMI data shows a negligible beam energy spread, we observe a 3%–5% contribution related to the beam in BTF sample. After correcting this effect, we obtain a global energy dependence of the energy resolution described by the formula ${\sigma _{E}}/{{E}_{{\rm {dep}}}}= {a}/\sqrt {{{E}_{{\rm {dep}}}}/{\hbox{GeV}}} \oplus {b}$ , with ${a} = ({0.59} \pm {0.12})\%$ and ${b} = ({3.63} \pm {0.21})\% $ . The simulation is in good agreement with data if we add an additional contribution due to the intrinsic LYSO fluctuation of 2.6%. We present also the measurements of the time resolution. The measurements have been performed using the ${e^ -}$ beam BTF in the energy range from 100 to 400 MeV. A resolution of ( ${161} \pm {3}$ ) ps at 100 MeV has been achieved. The energy dependence of the resolution has been fitted with following parametrization: ${\sigma _{\rm t}}{\rm (E)} = {a}/\sqrt {{E}/{\hbox{GeV}}} \oplus {b}$ , where the stochastic term and the constant term are determined to be ${a} = ({50} \pm {1})$ ps and ${b} = ({40} \pm {3})$ ps, respectively.