Speakers
Description
The use of silicon photomultipliers (SiPMs) as light sensors for Ring-Imaging Cherenkov (RICH) detectors operating in high magnetic fields is a promising option. Recent advances in SiPM technology in terms of near ultraviolet photon detection efficiency, time resolution and radiation hardness suggest the possibility of designing an innovative and challenging compact and fast RICH system for combined angular and Cherenkov-based timing measurements. The Cherenkov photon detector surface will consist of a SiPM sensor array integrating the front-end electronics in an hybrid stacked configuration. In this context, a dedicated R&D is in progress for the charged particle identification (PID) system of the ALICE 3 experiment proposed for the LHC Run 5 and beyond.
The proposed system is based on a proximity-focusing RICH configuration including an aerogel radiator separated from the SiPM array layer by an expansion gap. A thin high-refractive index slab of transparent material (“window”), acting as a second Cherenkov radiator, is glued on the SiPM array to improve the timing performance for time-of-flight measurements of charged particles thanks to production of Cherenkov photons in the window. In this way, we improve the pattern recognition for the ring angle reconstruction and suppress the background requiring a proper time matching between photons produced in the two radiators.
We assembled a small-scale prototype instrumented with different Hamamatsu SiPM array sensors with pitches ranging from 1 to 3 mm, readout by custom boards equipped with the front-end PETIROC 2A ASICs to measure charges and times with a 40ps-bin TDC. The Cherenkov radiators consisted of a 2 cm thick aerogel tile with a refractive index of 1.03. Different window materials (eg. SiO$_2$, MgF$_2$) were used. The prototype was successfully tested in a campaign at the CERN PS T10 beam line with pions, protons and electrons. We have measured a charged particle detection efficiency above 99%, a single photon angular resolution better than 4 mrad with time resolution better than 70 ps on the tracks of charged particles. With these results in hand, we expect for the full scale system an e/$\pi$ and $\pi$/K separation better than 3𝜎 up to 3 and 10 GeV/c, respectively.
The present technology makes the proposed SiPM-based PID system attractive also for future high-energy physics experiments and for space applications. In this contribution, the proposed RICH layout will be illustrated and the beam test results for the detector prototype will be presented.
