Speaker
Description
Precise timing at the tens of picoseconds level over large detector areas is a key challenge for experiments such as the SHiP experiment. Conventional double-sided readout of long plastic scintillator bars is limited to ~100 ps resolution due to photon transport effects. We present a novel geometry based on distributed SiPM readout along the bar, improving both timing and position reconstruction while increasing detector multiplicity for high-rate environments. Results from simulations and test beams using the FASTIC+ ASIC show a clear performance gain compared to side readout, approaching the sub-50 ps regime required for next-generation timing layers.
Summary (500 words)
Achieving precise timing at the level of tens of picoseconds over large detector surfaces is a key challenge for next-generation experiments such as SHiP experiment. In plastic scintillator–based timing detectors, the conventional approach relies on double-sided readout of long bars, where the interaction position is reconstructed from the time difference between signals collected at both ends. While robust, this technique typically reaches a practical limit of about 100 ps time resolution due to the combined effects of photon propagation fluctuations, sensor response, and electronic jitter.
In this work, we present a novel SiPM-based sensor geometry designed to overcome this limitation by rethinking the light collection scheme in long plastic scintillator bars. Instead of relying solely on end readout, the proposed configuration distributes silicon photomultipliers along the length of the bar, enabling a more localised and uniform detection of scintillation photons. This approach reduces the impact of photon path length dispersion and improves both timing precision and position reconstruction.
The proposed geometry also introduces a significant advantage in terms of detector multiplicity. By segmenting the readout along the bar, the system effectively increases the number of independent detection channels per unit length, which is particularly relevant for operation in high-rate environments. This feature allows for improved pile-up handling and scalability in large-area timing layers, such as the envisioned 4 m × 6 m detector plane.
The performance of this concept is evaluated through a combination of detailed simulations and experimental measurements obtained in test beam campaigns. Dedicated setups were instrumented using the FASTIC+ ASIC front-end electronics, which provide precise time-of-arrival and time-over-threshold measurements. Several configurations were studied, including comparisons between distributed readout and traditional double-sided readout of the same scintillator bars.
A systematic comparison of different SiPM technologies was also performed, focusing on devices from FBK and Hamamatsu. The results highlight the impact of photon detection efficiency, timing response, and noise characteristics on the overall system performance. In particular, the distributed geometry shows a clear improvement in timing resolution, reaching values significantly below the 100 ps benchmark and approaching the regime required for future precision timing applications.
Test beam data further confirm the advantages of the proposed approach, demonstrating enhanced timing performance, improved spatial resolution, and increased robustness against edge effects and non-uniformities. The comparison with side readout configurations clearly illustrates the limitations of the conventional method and the benefits of the new geometry.
These results represent a significant step toward the realisation of large-area timing detectors with sub-100 ps and ultimately sub-50 ps resolution. The proposed concept provides a scalable and efficient solution for high-rate environments and constitutes a strong candidate for the timing layer of the SHiP experiment, where precise time measurements are essential for background rejection and event reconstruction.