  The light yield of a small undoped cesium iodide (CsI) crystal directly
coupled with two silicon photomultipliers (SiPMs) at about 77~Kelvin was
measured to be $43.0 \pm 1.1$~photoelectrons (PE) per keV electron-equivalent
(keV$_\text{ee}$) using $X$ and $\gamma$-ray peaks from an $^{241}$Am
radioactive source from 18 to 60 keV. The high light yield together with some
other technical advantages illustrate the great potential of this novel
combination for neutrino and low-mass dark matter detection, particularly at
accelerator-based neutrino sources, where random background can be highly
suppressed by requiring coincident triggers between SiPMs and beam pulse timing
signals. Some potential drawbacks of using cryogenic SiPMs instead of
photomultiplier tubes (PMTs) were identified, such as worse energy resolution
and optical cross-talks between SiPMs. Their influence to rare-event detection
was discussed and possible solutions were provided.
