The Mu2e Calorimeter Photosensors

A “custom” modular SiPM layout has been chosen to enlarge the active sensor area and maximize the number of collected photoelectrons from the crystal. To well match the wavelength of the emitted light produced by the CsI crystals the SiPMs have to be extended in the UV region. A configuration in series has been chosen to overcome the issues related to the parallel connection which might affect the energy and time measurements, as due to the very large capacitance that may result in an increased noise, signal rise time and width. The design, production and tests on these SiPMs will be shown.