A SiPM-Based RICH Detector with Timing Capabilities for Isotope Identification

TL;DR

We address the need for compact, fast particle identification by integrating a Ring-Imaging Cherenkov detector with Time-of-Flight in a single SiPM-based photodetector layer. The authors build and beam-test small-scale prototypes using aerogel and a thin fused-silica radiator window, achieving a per-channel timing of about $35~\text{ps}$ and a Cherenkov-angle resolution around $4.2~\text{mrad}$, with $35$–$40$ photoelectrons per event and >$99.5\%$ efficiency. They explore configurations for light-isotope identification, including a proximity-focused RICH with a top TOF layer and a dual-RICH layout, supported by fast simulations that scale Cherenkov yields with $Z^2$ and estimate mass-separation up to $18~\text{GeV}/c$, $270~\text{GeV}/c$, and $300~\text{GeV}/c$ for the respective configurations. The work demonstrates feasibility of a compact, low-mass PID detector suitable for space applications, while highlighting engineering challenges and the need for detailed optimization in integration with spectrometers.

Abstract

In this work, we present a novel compact particle identification (PID) detector concept based on Silicon Photomultipliers (SiPMs) optimized to perform combined Ring-Imaging Cherenkov (RICH) and Time-of-Flight (TOF) measurements using a common photodetector layer. The system consists of a Cherenkov radiator layer separated from a photosensitive surface equipped with SiPMs by an expansion gap. A thin glass slab, acting as a second Cherenkov radiator, is coupled to the SiPMs to perform Cherenkov-based charged particle timing measurements. We assembled a small-scale prototype instrumented with various Hamamatsu SiPM array sensors with pixel pitches ranging from 2 to 3 mm and coupled with 1 mm thick fused silica window. The RICH radiator consisted of a 2 cm thick aerogel tile with a refractive index of 1.03 at 400 nm. The prototype was successfully tested in beam test campaigns at the CERN PS T10 beam line with pions and protons. We measured a single-hit angular resolution of about 4 mrad at the Cherenkov angle saturation value and a time resolution better than 50 ps RMS for charged particles with Z = 1. The present technology makes the proposed SiPM-based PID system particularly attractive for space applications due to the limited detector volumes available. In this work, we present beam test results obtained with the detector prototype and we discuss possible configurations optimized for the identification of ions in space applications.

Figures (6)

• Figure 1: Prototype artist view showing the two-cylindrical vessel prototype and schematic of the proposed SiPM-based RICH-TOF system: (a) The upstream vessel houses two SiPM arrays (A0 and A1) at a distance of about 15 cm; (b) the downstream vessel houses the ring arrays (RAs) to collect the Cherenkov photons produced by the 2 cm thick aerogel radiator (located 23 cm upstream) and a central array (A2) to detect the hit produced by the charged particle in the thin window glued on the SiPM array, as shown in (d); (c) a photo of the photodetector layer is shown with the RAs and A2.
• Figure 2: (Left plot): Distribution of the time differences by using the channels of S13361-2050AE-08 for A0 and S13361-3075AE-08 for the A2 arrays with 1 mm of fused silica glued on them. The histogram is fitted with two Gaussian distributions. The sigma of the core of the distribution (red line) is about 46 ps, while the sigma of the tail (green line) is about 93 ps. (Right plot): Cherenkov angle distribution measured with a 2 cm aerogel radiator and a proximity gap of about 23 cm by using a 2 mm SiPM pixel pitch. The single hit angular resolution is about 4.2 mrad in sigma unit Mazziotta:2025zxj.
• Figure 3: The figure shows two possible configurations for isotope identification. The left panel shows a proximity-focusing RICH with a dedicated top layer of TOF detector, made for instance of LGADs or SiPMs with a thin radiator window. The right panel illustrates a dual-RICH system with an aerogel and a NaF radiator, respectively.
• Figure 4: Expected average number of detected hits as a function of the momentum for electrons, protons and light nuclei for the aerogel- and NaF-based RICH configuration, respectively.
• Figure 5: Separation power as a function of the momentum for electron-proton, proton-D and other various nuclei pairs for the TOF, NAF and aerogel RICH configuration (see text), respectively.