Beam test studies for a SiPM-based RICH detector prototype for the future ALICE~3 experiment

TL;DR

This work validates a prototype of the ALICE3 barrel RICH (bRICH) using a proximity‑focusing design with an aerogel radiator ($n=1.03$) and SiPM sensors. The CERN‑PS T10 beam test demonstrates a single‑photon angular resolution near $3.8$ mrad and a ring‑level resolution consistent with $1/\sqrt{N_{ph}}$ scaling, supporting effective $e/\pi$, $\pi/K$, and $K/p$ separation in the intended momentum ranges. Timing information is shown to suppress background significantly, enabling robust Cherenkov angle reconstruction in a high‑multiplicity environment. The results underpin the ALICE3 bRICH feasibility and inform planned hardware upgrades, larger readout pixels, and irradiation studies to ensure performance under realistic operating conditions.

Abstract

The ALICE Collaboration is proposing a completely new apparatus, ALICE~3, for the LHC Runs~5 and beyond. In this context, a key subsystem for high-energy charged particle identification will be a proximity-focusing ring-imaging Cherenkov detector using aerogel as radiator and silicon photomultipliers (SiPMs) as photon sensors. We assembled a small-scale prototype instrumented with Hamamatsu S13352 and S13361-3075AE-08 SiPM arrays, readout by custom boards equipped with front-end Petiroc 2A ASICs. The Cherenkov radiator consisted of a 2 cm thick hydrophobic aerogel tile with a refractive index of 1.03 separated from the SiPM plane by a 23 cm expansion gap. The prototype was successfully tested in a campaign at the CERN PS T10 beam line with the goal of validating the design bRICH specifications in terms to achieve the target separation power. We measured a single photon angular resolution of 3.8~mrad at the Cherenkov angle saturation value of 242~mrad, as well as the expected scaling of the angular resolution with the increasing number of detected photons. We also studied the contribution of uncorrelated and correlated background sources with respect to the signal and proved the effectiveness of time matching between charged tracks and photon hits to achieve efficient suppression of the SiPM dark count rate background. In this paper, the detector concept, the description of the tested prototype layout and the main beam test results are reported.

Figures (12)

• Figure 1: Top panel: Photo of the beam test set-up at CERN PS T10 line on Oct, 2023. The beam enters from the right side. The black boxes upstream and downstream the aluminium vessel in the middle house thin plastic scintillator tiles and a X-Y fiber tracker module MAZZIOTTA2022167040. Middle panel: CAD view of the RICH vessel with the aerogel tile and the endcap photon detector plate. Bottom panel: photon detector plate with S13552 SiPM linear array and downstream SiPM S13661-3075AE-08 array.
• Figure 2: Picture (top) and block diagram (bottom) of one of the boards used for data acquisition MAZZIOTTA2022167040.
• Figure 3: Spatial distribution of the extrapolated X-Y emission points in the median plane of the aerogel tile (central region) and of the hits in the eight ring arrays (ring region) for the negative charged beam at 10 GeV/$\it{c}$ momentum (top panel) and the positive charged beam at 8 GeV/$\it{c}$ momentum (bottom panel). For guiding the eyes, the expected Cherenkov rings from pions and protons centered in the most probable X-Y emission point are also shown.
• Figure 4: Distribution of the time differences between the array cell firing time $\text{t}_{\text{hit}}$ and the firing time $\text{t}_{\text{track}}$ of the central array charged particle cluster cell with maximum number of PEs in the events with the negative charged beam at 10 GeV/$c$ momentum (top panel) and with the positive charged beam at 8 GeV/$c$ momentum (bottom panel).
• Figure 5: Distribution of the reconstructed aerogel single photon Cherenkov radius for the negative charged beam at 10 GeV/$c$ momentum (left column) and for the positive charged beam at 8 GeV/$c$ momentum (right column). The bottom plots show the distribution requiring hit-track matching in a $\pm 5$ ns time window. The vertical bars represent the statistical uncertainties. The fit with the sum of a Gaussian for the pion peak (or two Gaussians for the pion and proton peaks) and our template background distribution is also shown.