Advances in photocathode development for PICOSEC Micromegas precise-timing detectors

TL;DR

This paper reports on the development and characterization of photocathodes for PICOSEC Micromegas detectors, achieving record timing resolution of 10.9 ps with CsI and exploring robust alternatives like Ti and B4C.

Contribution

It provides a comprehensive study of various photocathodes, highlighting the best materials for precise timing and robustness in PICOSEC Micromegas detectors.

Findings

CsI photocathode achieved 10.9 ps time resolution with >30 photoelectrons.

Titanium and B4C photocathodes reached ~30 ps with ~5 photoelectrons.

Robust photocathodes can maintain excellent timing performance.

Abstract

The PICOSEC Micromegas detector is a precise-timing gaseous detector that combines a Cherenkov radiator, a semi-transparent photocathode and a Micromegas amplification stage, targeting time resolutions of tens of picoseconds for minimum ionising particles (MIPs). Initial single-pad prototypes achieved $\sigma<25$ ps, demonstrating strong potential for High Energy Physics (HEP) applications. The objective of this paper is a~comprehensive characterisation of photocathodes, with a strong focus on robust materials while preserving excellent timing performance. The study includes laboratory measurements of optical and resistive properties together with beam tests using 150 GeV/$c$ muons to evaluate time resolution and photoelectron yield for various photocathodes. The best performance was delivered by a~5\,nm Cesium Iodide (CsI) photocathode, reaching $\sigma = 10.9 \pm 0.3$ ps with more than 30 extracted photoelectrons, representing the most precise time resolution achieved by PICOSEC Micromegas to date. Metallic and carbon-based photocathodes, including Titanium (Ti), Boron Carbide (B$_4$C) and Diamond-Like Carbon (DLC), were also tested, with Ti and B$_4$C emerging as the most promising alternatives, achieving $\sigma \approx 30$ ps with about 5 extracted photoelectrons. These results demonstrate that improved robustness can be achieved while maintaining excellent time resolution, supporting the feasibility of using the PICOSEC Micromegas concept in future experiments.