Speaker
Description
One of the best time resolution for single charged particles has been achieved using a photomultiplier tube based on microchannel plates (MCP-PMT) coupled with a Cherenkov radiator. The main problem of MCP-PMT is its limited lifetime due to photocathode degradation. The degradation is considered to be caused by feedback ions that bombard the photocathode and affect its photoemissive properties. This issue can be mitigated by using a more stable photocathode material, such as CsI, or by using a photocathode geometry in which the emissive layer is less affected by the feedback ions.
We prepared a detector prototype exploiting both these approaches and studied its timing properties with particle beams. The prototype consists of a magnesium fluoride (MgF$_2$) Cherenkov radiator, a cesium iodide (CsI) photocathode, and microchannel plates (MCP). Besides the conventional semitransparent photocathode directly deposited on the MgF$_2$ radiator, we tested photocathodes deposited on the MCP surface and on a metal mesh placed in front of the MCP. The latest two configurations are intended to extend the photocathode lifetime by preventing bombardment of the photoemissive material by feedback ions. For these configurations, radiators with a structured surface have been manufactured to allow Cherenkov photons to exit the radiator and reach the photocathode.
The obtained time resolutions for single charged particles are 12 ps, 9 ps, and 7.6 ps for mesh-based, MCP-based, and semitransparent photocathode, correspondingly.
Measurement of the time-of-flight with 10 ps accuracy at a distane of about 3 m could provide π/K separation up to 6 GeV/c, that might be useful to enhnce PID capability at the endcap regions of the CEPC detector.
