Silica aerogel radiator for use in the A-RICH system utilized in the Belle II experiment

Abstract

This paper presents recent progress in the development and mass production of large-area hydrophobic silica aerogels for use as radiators in the aerogel-based ring-imaging Cherenkov (A-RICH) counter, which will be installed in the forward end cap of the Belle II detector. The proximity-focusing A-RICH system is especially designed to identify charged kaons and pions. The refractive index of the installed aerogel Cherenkov radiators is approximately 1.05, and we aim for a separation capability exceeding 4σ at momenta up to 4 GeV/c. Large-area aerogel tiles (over 18 × 18 × 2 cm 3 ) were first fabricated in test productions by pin drying in addition to conventional methods. We proposed to fill the large end-cap region (area 3.5 m 2 ) with 124 water-jet-trimmed fan-shaped dual-layer-focusing aerogel combinations of different refractive indices (1.045 and 1.055). Guided by the test production results, we decided to manufacture aerogels by the conventional method and are currently proceeding with mass production. In an electron beam test undertaken at the DESY, we confirmed that the K/π separation capability of a prototype A-RICH counter exceeded 4σ at 4 GeV/c.

Developing a silica aerogel radiator for the HELIX ring-imaging Cherenkov system

“…Note that in principle water itself does not affect the aerogel optical properties due to a hydrophobic surface modification applied to the aerogel. The target transparency is comparable with the design of the downstream aerogel layer (a transmission length of 30 mm for n = 1.055) of the ARICH detector in the Belle II spectrometer at Japan's High Energy Accelerator Research Organization (known as KEK) [7], which is a model of the HELIX RICH detector.…”

“…However, subsequent studies significantly improved the density (i.e., refractive index) uniformity of pin-dried aerogels (data unpublished but see also Ref. [7]). We expect our recent aerogels will meet the exact requirement.…”

Development of a 144-channel Hybrid Avalanche Photo-Detector for Belle II ring-imaging Cherenkov counter with an aerogel radiator

“…With this scheme, we can increase the number of photons without degrading the single photon Cherenkov angle resolution [7]. Two 20 mm-thick aerogel tiles with the refractive indices of 1.045 and 1.055 will be used in the Aerogel RICH for upstream and downstream radiators [8].…”

Large-area silica aerogel for use as Cherenkov radiators with high refractive index, developed by supercritical carbon dioxide drying

“…This counter is installed at the forward end cap region and requires a large number of transparent silica aerogel tiles with different refractive indices as the Cherenkov radiator [15]. Figure 1 shows the planned aerogel radiator tiling of the A-RICH counter [16]. In this tiling plan, a cylindrical area of 3.5 m 2 is covered with two layers of large-area aerogel tiles segmented into 124 blocks, each of thickness 2 cm (i.e., a total of 248 tiles).…”