Efficient and precise Cherenkov-based charged particle timing using SiPMs

TL;DR

This work investigates efficient and precise Cherenkov-based particle timing by coupling a thin high-index radiator, notably fused silica, to SiPM arrays. A Monte Carlo framework quantifies the time resolution contributions from photon-path spread, chromatic dispersion, SiPM SPTR, and electronics jitter, using realistic PDEs and multiple readout channels. Results indicate sub-30 ps timing is achievable for radiator thicknesses around 1 mm, with thicker radiators and multi-channel averaging further improving resolution, in agreement with beam-test data. The study provides design guidance for radiator thickness and sensor configuration and highlights integration prospects with RICH detectors for compact, fast ToF systems in high-energy physics.

Abstract

Dedicated R&D efforts are currently underway to couple a thin Cherenkov radiator to Silicon Photomultiplier (SiPM) arrays for precise charged particle Time-of-Flight (ToF) measurements. The prompt nature of Cherenkov radiation makes it an ideal candidate for achieving ultimate timing performance in a ToF detector. Using a thin radiator with a high refractive index, such as fused silica, enables the generation of a fast signal from charged particles that exceed the Cherenkov threshold. A crucial requirement for approaching the target time resolution is the optimization of both the radiator material and thickness, as well as the optical coupling to the SiPM arrays. In this work, we present the main factors that affect the time resolution and the expected performance achieved through a detailed Monte Carlo simulation and the comparison with beam test results.

Figures (4)

• Figure 1: Cherenkov momentum threshold as a function of the refractive index $n$ for various charged particle species (electrons, muons, pions, kaons, protons). The vertical dashed lines indicate the refractive indices of common radiator materials: NaF, $\text{MgF}_2$, and fused silica ($\text{SiO}_2$) at $\approx$ 400 nm.
• Figure 2: Conceptual sketch depicting the optical coupling of a thin Cherenkov radiator with a SiPM array. The blue shaded area represents the possible trajectories of Cherenkov photons generated along the path of the incident charged particle. The yellow pixels indicate the SiPMs fired by the Cherenkov photons, neglecting possible reflections.
• Figure 3: Expected time resolution as a function of a fused silica radiator thickness. Colored lines show the different contributions. The maximum spread of photon arrival time is calculated according Eq.\ref{['eq:dtmax']} weighted with the Cherenkov photons emission spectrum in the wavelength range from 260 nm to 900 nm and the SiPM PDE.
• Figure 4: Top panel: collected photoelectrons in the three highest-hit pixels as a function of the fused silica radiator thickness. Bottom panel: time resolution as a function of the fused silica radiator thickness, calculated using the three channels with the highest observed charge. Three SiPM configurations are considered: (i) 3 mm ($75 \, \mu\text{m}$ microcell); (ii) 2 mm ($50 \, \mu\text{m}$ microcell); and (iii) 1 mm ($50 \, \mu\text{m}$ microcell). The black filled circle represent the single SiPM resolution derived from the experimental results reported in Refs. Mazziotta:2025zxjparticles8040094 (see text for details).