Measurement of time resolution of the Mu2e LYSO calorimeter prototype

In this paper we present the time resolution measurements of the Lutetium-Yttrium Oxyorthosilicate (LYSO) calorimeter prototype for the Mu2e experiment. The measurements have been performed using the $e^{-}$ beam of the Beam Test Facility (BTF) in Frascati, Italy in the energy range from 100 to 400 MeV. The calorimeter prototype consisted of twenty five 30x30x130 mm${}^3$, LYSO crystals read out by 10x10 mm${}^2$ Hamamatsu Avalanche Photodiodes (APDs). The energy dependence of the measured time resolution can be parametrized as ${\sigma }_t(E)=a\mathrm{/}\sqrt{E\mathrm{/}\mathrm{G}\mathrm{e}\mathrm{V}}\oplus b$, with the stochastic and constant terms $a=(51\pm 1)$ ps and $b=(10\pm 4)$ ps, respectively. This corresponds to the time resolution of ($162\pm 4$) ps at 100 MeV.