Study of a threshold Cherenkov counter based on silica aerogels with low refractive indices

Abstract

To identify π ± and K ± in the region of 1.0 ∼ 2.5 GeV/c, a threshold Cherenkov counter equipped with silica aerogels has been investigated. Silica aerogels with a low refractive index of 1.013 have been successfully produced using a new technique. By making use of these aerogels as radiators, we have constructed a Cherenkov counter and have checked its properties in a test beam. The obtained results have demonstrated that our aerogel was transparent enough to make up for loss of the Cherenkov photon yield due to a low refractive index. Various configurations for the photon collection system and some types of photomultipliers, such as the fine-mesh type, for a read out were also tested. From these studies, our design of a Cherenkov counter dedicated to π/K separation up to a few GeV/c with an efficiency greater than 90 % was considered.

Progress in Development of Silica Aerogel for Particle- and Nuclear-Physics Experiments at J-PARC

“…To generate silica wet gels, the classic KEK method uses hydrolysis, condensation, and polymerization between a type of siloxane and water with the help of an aqueous ammonia solution as the catalyst. The most basic solvent in the wet-gel synthesis process is methanol; instead, the KEK-Matsushita group used ethanol when they produced aerogels with n < 1.02 to obtain long transmission lengths [3]. Currently, DMF is persistently used as a solvent to fabricate aerogels with n > 1.04 (the modernized KEK method) [1].…”

“…We fabricated aerogels with densities varying from 0.02 to 0.2 g/cm 3 using the conventional method with ethanol or DMF as a solvent, and they were systematically tested for muonium emission yield by the E34 Collaboration [28]. Recently, the enhancement of the muonium emission rate has been observed using an aerogel with a density of approximately 0.03 g/cm 3 and a laser-ablated surface [26].…”

“…These aerogels were mass produced using the classic KEK method described in Refs. [3,4] and were used in the aerogel Cherenkov counters [4,5] of the Belle experiment [6] at the High Energy Accelerator Research Organization (KEK). At that time, the classic method allowed us to produce aerogels with a maximum index of refraction of 1.10; however, for practical use, the transmission length had to be improved.…”

“…In addition, it was impossible to produce aerogels with n > 1.14 with the sol-gel method [1]. For low indices of refraction, aerogels with n = 1.008 (density of 0.03 g/cm 3 ) were used for capturing cosmic dust at low earth orbit in the MicroParticles Capturer (MPAC) experiment implemented by the Japan Aerospace Exploration Agency aboard the International Space Station (e.g., Ref. [7]).…”

“…Moreover, the pin-drying method enabled us to produce aerogels with transmission lengths up to 60 mm and with an index of refraction n = 1.05 to 1.075 [13][14][15][16]. In contrast to these high-refractiveindex aerogels, ultralow-density aerogels with n = 1.003 (ρ = 0.01 g/cm 3 ) were developed using the classic method [13]. In the present study, we report the most recent updates to these aerogel production methods.…”