Development of a picosecond-timing Cherenkov detector using gaseous photomultiplification

Photosensitive gaseous detectors with a simple photoelectron multiplication mechanism as resistive plate chambers are expected to offer both large photo coverage and excellent time resolution while keeping costs low. We have developed a gaseous photomultiplier (GasPM) and demonstrated that a single-photon time resolution is $25\pm1.1~\rm{ps}$ at the gain of $3.3\times10^6$ with a $\rm {LaB_6}$ photocathode, which has an extremely low quantum efficiency. We then developed a Cherenkov detector using GasPM with a $\rm{CsI}$ photocathode aiming for an application in time-of-flight measurements with a resolution below 10~$\rm{ps}$ for particle identification. We performed a test using the 3 GeV electron beam at the PF-AR test beamline located at KEK, Japan. As a result, the resolution of time-of-flight between the detector and an MCP-PMT is measured to be $\sigma=73.0\pm2.4~\rm{ps}$. The obtained resolution is worse than the target because of the lower gap voltage compared to the design. However, it is consistent with the expectation from the applied gap voltage. It is an important milestone for achieving the designed resolution by increasing the gap voltage and photon detection efficiency in future development.