Speaker
Description
To meet the growing demand for photosensors with high time resolution, large photocoverage, and low cost in Cherenkov imaging detectors, we have developed a gaseous photomultiplier (GasPM). It has a photocathode and a simple electron multiplication mechanism similar to that of resistive plate chambers. Using a picosecond pulse laser, we have already demonstrated that the GasPM with a LaB$_6$ photocathode and a mixture of R134a and SF$_6$ gas has a single-photon time resolution of $\sigma=25 \pm 1.1$ ps at a gain of $3.3 \times 10^6$. The next milestone of the R$\&$D is to detect Cherenkov photons with that excellent time resolution.
The photocathode was replaced with CsI deposited on a MgF$_2$ window, which can detect Cherenkov photons at wavelengths below 200 nm generated in the window. We performed beam tests of this detector with a 5 GeV electron beam at the PF-AR test beamline at KEK. We achieved a time resolution of $\sigma=73.0 \pm 2.4$ ps with a gap electric field of 140 kV/cm. To improve the time resolution, the thickness of the MgF$_2$ window and the gap electric field were increased to 187 kV/cm. In addition, a digitizer with a higher sampling rate of 10 Gsamples/sec was used to distinguish between overlapping initial signal pulse and subsequent ones due to photon feedback.
The results of these beam tests will be discussed in this presentation.
