Test beam performance of a novel RICH detector with timing capabilities for the future ALICE~3 PID system at LHC

TL;DR

The paper addresses the challenge of achieving precise particle identification for ALICE 3 at the LHC using a timing‑capable RICH detector. It presents beam‑test results from small‑scale prototypes employing a $2~\mathrm{cm}$ aerogel radiator ($n=1.03$ at $400~\mathrm{nm}$) and a thin window radiator, read out by SiPM arrays and synchronized with Radioroc 2/picoTDC electronics. The measurements show a single‑photon angular resolution of about $4.2~\mathrm{mrad}$ at Cherenkov saturation and a relative timing resolution around $46$ ps (sigma) between timing channels, corresponding to roughly $30$ ps per SiPM, with strong background suppression through time matching. These findings align with the ALICE 3 bRICH specifications and demonstrate feasibility for a timing‑capable RICH in the future detector.

Abstract

The ALICE Collaboration is proposing a completely new apparatus, ALICE 3, for the LHC Run 5 and beyond. A key subsystem for charged particle identification will be a Ring-Imaging Cherenkov (RICH) detector consisting of an aerogel radiator and a photosensitive surface based on Silicon Photomultiplier (SiPM) arrays in a proximity-focusing configuration. A thin high-refractive index slab of transparent material (window), acting as a second Cherenkov radiator, is glued on the entrance face of the SiPM arrays to achieve precise charged particle timing. Requiring time matching between aerogel Cherenkov photon and track hits leads to an improvement of pattern recognition by discarding the uncorrelated SiPM dark count hits. In this work we present the current status of the R\&D performed for the ALICE 3 RICH detector prototype and the expected full scale system performance. A special focus will be given to the beam test results obtained with a small-scale prototype instrumented with various array of Hamamatsu SiPMs with pitches ranging from 1 to 3 mm. The Cherenkov radiator consisted of a 2 cm thick aerogel tile with a refractive index of 1.03 at 400 nm wavelength. For timing measurements SiPM arrays coupled with two different window materials (SiO$_2$ and MgF$_2$) were used. The prototype was successfully tested in beam test campaigns at the CERN PS T10 beam line. The data were collected with a complete chain of front-end and readout electronics based on the Petiroc 2A and Radioroc 2 together with a picoTDC to measure charges and times. We measured a charged particle detection efficiency above 99\% and a single photon angular resolution better than 4.2 mrad at the Cherenkov angle saturation with a time resolution better than 70 ps for charged particles.

Figures (2)

• Figure 1: Left: Beam test set-up at CERN PS T10 line on Sep/Oct, 2024. The beam enters from the right side. The two insets show and artist-view of the RICH prototype inside the cylinders. The black box in the set-up includes a X-Y fiber tracker module MAZZIOTTA2022167040. In the 2023 set-up, only one cylinder was used including the aerogel tile and two arrays along the beam line Mazziotta_IWORID. Right: A Crate housing the Radioroc2/picoTDC FEBs, each plugged on a MOSAIC board. The Samtec HLCD-20 cables are also shown to route the signals from the feed-through boards to the FEBs (see text for more details).
• Figure 2: Test beam results achieved in 2024 for the negative charged beam at 10 GeV/$\it{c}$ (mainly pions). Top: Cherenkov angle reconstruction as a function of the photon arrival times respect to the charged particle; Left bottom: Cherenkov angle distribution in a 10 ns time window; right bottom: M2-M0 timing performance.