Development of a silicon photomultiplier module for ACME III*

A search for the eEDM is one of the powerful ways to probe for the existence of physics beyond the standard model. The current upper limit of $1.1\times10^{-29}\,e\cdot$cm has been achieved by the ACME experiment II which used cold ThO polar molecules. One of the upgrade plans for the next generation ACME experiment is a new fluorescence detection system based on a silicon photomultiplier (SiPM). SiPMs have higher quantum efficiency, $\sim 50\%$ at 512 nm, than the normal PMTs used in ACME II. To use SiPMs for ACME III, we are designing a cooling system to reduce the dark count rate and a preamplifier and shaper to overcome the relatively slow bandwidth of SiPMs. We developed a prototype module and characterized its performance. We will present the current status of SiPM development including prototype tests.