An accurate measurement of PMT TTS based on the photoelectron spectrum

TL;DR

This paper presents a novel method using the photoelectron spectrum to accurately measure the transit time spread (TTS) of photomultiplier tubes, applicable to multiple photoelectrons simultaneously, crucial for water Cherenkov detector performance.

Contribution

It introduces a new measurement technique based on the photoelectron spectrum for determining TTS of PMTs, especially for multiple photoelectrons, improving accuracy and efficiency.

Findings

TTS of single photoelectron is 3.3 ns.

Method is suitable for multi-photoelectron TTS measurement.

The approach meets WCDA requirements.

Abstract

The water Cherenkov detector array (WCDA) for the large high altitude air shower observatory(LHAASO) will employ more than 3600 hemisphere 8 inch photomultiplier tubes (PMT). The good time performance of PMT, especially the transit time spread (TTS), is required for WCDA. TTS is usually defined as the TTS of single photoelectron, and usually determined by using single photoelectron counting technique. A method using the photoelectron spectrum is researched for the measurement of TTS. The method is appropriate for multi-photoelectrons and makes it possible to measure the TTS of different photoelectrons at the same time. The TTS of different photoelectrons is measured for Hamamatsu R5912 with the divider circuit designed in specifically. The TTS of single photoelectron is determined to 3.3 ns and satisfies the requirement of WCDA.