Fabrication of silica aerogel with $n$ = 1.08 for $e^+/\mu ^+$ separation in a threshold Cherenkov counter of the J-PARC TREK/E36 experiment

TL;DR

This paper reports the development and characterization of hydrophobic silica aerogel with a refractive index of 1.08, optimized for particle separation in Cherenkov counters used in the J-PARC TREK/E36 experiment.

Contribution

The study introduces a new fabrication process for crack-free silica aerogel with specific optical properties tailored for particle identification in a high-energy physics experiment.

Findings

Produced 30 crack-free aerogel blocks with desired refractive index and transparency.

Designed radiator blocks with trapezoidal shape for optimal detector fit.

Validated optical properties suitable for Cherenkov particle separation.

Abstract

This study presents the development of hydrophobic silica aerogel for use as a radiator in threshold-type Cherenkov counters. These counters are to be used for separating positrons and positive muons produced by kaon decay in the J-PARC TREK/E36 experiment. We chose to employ aerogel with a refractive index of 1.08 to identify charged particles with momenta of approximately 240 MeV/$c$, and the radiator block shape was designed with a trapezoidal cross-section to fit the barrel region surrounding the kaon stopping target in the center of the TREK/E36 detector system. Including spares, we obtained 30 crack-free aerogel blocks segmented into two layers, each layer having a thickness of 2 cm and a length of 18 cm, to fill 12 counter modules. Optical measurements showed that the produced aerogel tiles had the required refractive indices and transparency.