Test Measurements of Prototype Counters for CLAS12 Central Time-of-Flight System using 45 MeV protons

TL;DR

This study compares timing properties of two photomultiplier types for the CLAS12 TOF system, demonstrating the advantages of fine-mesh PMs, especially under magnetic fields, with improved timing resolution.

Contribution

It provides the first comparative measurements of magnetic-resistant R7761-70 and standard R2083 photomultipliers for CLAS12, highlighting the benefits of fine-mesh PMs in magnetic environments.

Findings

R7761-70 PMs have similar TOF resolution to R2083 PMs.

R7761-70 gain is unaffected by magnetic fields up to 1100 Gauss.

Timing resolution improves by about 8% at 1100 Gauss with R7761-70 PMs.

Abstract

A comparative measurement of timing properties of magnetic-resistant fine mesh R7761-70 and ordinary fast R2083 photomultipliers is presented together with preliminary results on the operation of R7761-70 PMs in magnetic field up to 1100 Gauss. The results were obtained using the proton beam of the MC50 Cyclotron of Korea Institute of Radilogical and Medical Sciences. The ratio of the effective R7761-70 and R2083 TOF (or timing) resolutions was extracted by using two different methods. The results are $1.05\pm 0.066$ and $1.07\pm 0.062$. The gain of R7761-70 PMs is not affected by magnetic field. The R7761-70 TOF/timing resolution becomes $\sim 8%$ better at 1100 Gauss if the external field is oriented parallel to the PM axis. The results prove the advantages of the design of the CLAS12 Central Time-of-flight system with fine-mesh photomultipliers in comparison with the "conservative" design based on ordinary R2083 PMs and long bent light guides.