Speaker
Description
The ALICE Collaboration is proposing a completely new apparatus, ALICE 3, to investigate the properties of the quark--gluon plasma in heavy-ion collisions during LHC Run 5. A key PID subsystem in the barrel region will be a proximity-focusing Ring-Imaging Cherenkov detector (bRICH). It will cover a radial region of 36 cm, using aerogel ($n = 1.03$) as radiator and silicon photomultipliers (SiPMs) as photon sensors. The detector is designed to ensure efficient e/$\pi$, $\pi$/K and K/p separation for momenta up to 2, 10 and 16 GeV/$c$, respectively. Filling the proximity gap with a CO$_2$-based gas mixture ($n = 1.0006$) allows the further extension of electron PID up to 4 GeV/$c$ through Cherenkov threshold-based pion discrimination to access unprecedented dielectron-related observables. The challenging requirement of preserving the target single-photon performance with SiPMs exposed to fluences corresponding to NIEL levels above $10^{11}$ 1-MeV n$_{\mathrm{eq}}$/cm$^2$ led to the design of a dedicated module concept based on radiation-hard components. The module concept is based on the DENEB front-end ASIC, targeting a single-photon time resolution of 100 ps. It also integrates two-phase microchannel CO$_2$ cooling of the SiPMs down to $-40^\circ$C, together with an annealing system capable of heating them above $70^\circ$C. In addition, we demonstrate that smaller SiPMs coupled to light concentrators made of fused silica can reduce the active area and the overall dark count rate (DCR), while preserving the same effective area, number of channels and spatial resolution, and improving the time resolution. Various small-scale prototypes were successfully tested in beam-test campaigns at the CERN-PS T9 and T10 beam lines. The measurements validated both the bRICH layout and the expected performance in terms of timing, photon yield, angular resolution, and the resulting separation power. They also demonstrated the stability of the reconstruction performance under the increasing DCR conditions expected during ALICE 3 operation. In this contribution, the bRICH concept, the latest detector R&D results, and the main beam-test results will be presented.