Development of a Cherenkov-Based Time-of-Flight Detector Using Silicon Photomultipliers

Abstract

The aim of this work is to develop high precision Time-of-Flight (TOF) devices based on high refractive index solid Cherenkov radiators read out by silicon photomultipliers (SiPMs). Cherenkov light is prompt and therefore ideal for reaching the intrinsic timing limits of TOF systems. By utilizing a thin, high-refractive-index radiator a nearly instantaneous signal is generated by particles exceeding the Cherenkov threshold. In order to achieve the ultimate time resolution, we carried out a rigorous optimization of the radiator material and geometry, alongside the efficiency of the optical coupling to the SiPM sensors. The key factors limiting the time resolution were characterized by comprehensive Monte Carlo simulations, subsequently validated against experimental beam test data. We assembled small-scale prototypes instrumented with various Hamamatsu SiPM arrays sensors with pitches ranging from 1.3 to 3 mm coupled with various window materials, such as fused silica and MgF2, featuring various thickness values. The prototypes were 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 either the Petiroc 2A or the Radioroc 2 interfaced to a picoTDC to measure charges and times. By comparing the time measurements with two SiPM arrays we were able to measure a time resolution better than 33.2 ps at the full system level with a charged particle detection efficiency of 100%. Our results demonstrate the expected performance benchmarks for the charged particle detection efficiency and time resolution and highlight the potential of the developed Cherenkov-based TOF detectors for next-generation particle identification systems.

Figures (19)

• Figure 1: Three-dimensional model of the radiator-sensor coupling. The incident particle track is shown passing through the radiator. The Cherenkov radiation is projected onto the SiPM array layer, highlighting the spatial correlation between the particle trajectory and the fired pixels. The red-orange area corresponds to the core of the emission, assuming negligible reflections at the radiator boundaries.
• Figure 2: Top left: Expected time resolution as a function of the SiO$_2$ radiator thickness. The colored curves represent the individual contributions to the total time resolution. Top right: Average number of fired pixels as a function of the radiator thickness. Bottom left: Average number of photoelectrons collected in the three pixels with the highest hit probability, shown as a function of the radiator thickness. Bottom right: Total time resolution as a function of the radiator thickness, computed using the timestamps from the three highest‑charge channels. Three SiPM configurations are investigated: 3 mm active area with a $75\;\upmu\text{m}$ SPAD size, 2 mm active area with a $50\;\upmu\text{m}$ SPAD size, and 1.3 mm active area with a $50\;\upmu\text{m}$ SPAD size.
• Figure 3: Schematic view of the detector stack, including the environmental gas, the window, and the SiPMs. The SiPM structure includes the protective resin, the ARC, the passivation layer, and silicon.
• Figure 4: Top: Schematic view of the beam test setup. Bottom: Photographs of the cylindrical vessel housing the arrays A0 and A1, and connection to the Front-End boards.
• Figure 5: ToT measured from the digital output signal of the Radioroc 2, which is given as input to the picoTDC, versus shaper charge measured from the analog probe output of the shaper (left panel). The measurements were performed with an oscilloscope while illuminating a single SiPM with a laser. The one-dimensional projections of the ToT and charge are displayed.