Designing the ALICE 3 bRICH detector: Simulation studies and beam test results

The ALICE Collaboration is proposing a completely new apparatus, ALICE 3, for the LHC Run 5. The design target of the ALICE 3 charged particle identification (PID) system is to ensure a better than 3σe/π, π/K and K/p separation for momenta up to 2 GeV/c, 10 GeV/c and 16 GeV/c, respectively. A key PID subsystem in the barrel region (|η|<2) will be a proximity-focusing Ring-Imaging Cherenkov detector, the bRICH, using aerogel (n=1.03 at 400 nm) as radiator and silicon photomultipliers (SiPMs) as photon sensors. The system must be optimized to enable an efficient PID in the high-multiplicity environment of Pb–Pb collisions. Dedicated reconstruction machine-learning based algorithms were developed to prove the physics reach of the proposed bRICH layout. Various small-scale prototypes instrumented with hydrophobic aerogel tiles by Aerogel Factory Co., Ltd., and Hamamatsu SiPM arrays read out by custom boards equipped with front-end Petiroc 2A or Radioroc 2 Weeroc chips coupled with PicoTDC ASICs, were successfully tested in beam test campaigns at the CERN-PS T10 and T9 beam lines between 2022 and 2025. Our measurements validated both the bRICH design and the expected performance in terms of photon yield, angular resolution and separation power. In this paper, the bRICH concept, the expected performance from simulations and beam test results are reported.