Performance of a silicon photomultiplier module for the ACME III electron EDM search*

A measurement of the electron electric dipole moment (eEDM) is a powerful probe for the existence of physics beyond the Standard Model of particle physics. The ACME experiment searched for the eEDM with the world's highest sensitivity using cold ThO polar molecules (Nature, 562 (2018) 355-360). One of the improvements for the next generation of the ACME experiment is using silicon photomultipliers (SiPMs) as laser-induced fluorescence photon detectors instead of PMTs. We have developed a dedicated SiPM module and evaluated its performance. The SiPM module shows about 2.5 times higher detection efficiency than the PMTs used in the previous ACME measurement. Here we report on the design and performance of the SiPM module.