Modeling Scintillation Photon Transport and Reconstruction Algorithms for the Time-of-Flight Detector in the T2K Neutrino Experiment

Abstract

The T2K ND280 upgrade aims to reduce the systematic uncertainty of the CP-violating phase, $δ_{CP}$, to reject non-CP violation hypothesis at $3σ$ confidence level. A crucial component of the ND280 upgrade, alongside the Super Fine Grained Detector (SuperFGD) and two High-Angle Time Projection Chambers (TPCs), is the Time-of-Flight (ToF) detector, which significantly enhances background rejection and particle identification capabilities. The ToF detector features six modules in a cube configuration, each with 20 plastic scintillator bars measuring $\text{220}\times\text{12}\times\text{1}\,\text{cm}^3$ and is equipped with Silicon Photomultiplier (SiPM) arrays at both ends to capture scintillation light. This letter outlines the modelling of the detector response and the signal reconstruction process.

Figures (14)

• Figure 1: 3D view of the ToF system, composed of six modules arranged in a cube. Each module houses 20 plastic scintillator bars, covering an active area of 5.4 m². The bars are mounted in a plane with 1.5 mm gaps to accommodate steel brackets on the aluminium frame. In the bottom module, two bars are removed to provide space for cable trays.
• Figure 2: Layout of MPPC sensors and 3D printed protective capsule at the readout end of the bar.
• Figure 3: Sketch of the single-bar test-bench. The trajectories of photons reaching the sensor directly (blue and yellow) and after reflection at the far end (orange) are shown, together with the two MPPC readout ends (Left and Right) and the two reference photomultiplier hodoscopes. The expected waveforms from both readout ends are also illustrated.
• Figure 4: Left: Photon arrival times to the closer sensor (continuous line) and the far one (dashed line). The arrival times are shown for several minimal distances: 10 cm (black), 50 cm (red), 80 cm (green) and the middle of the bar (blue). Right: Waveforms were obtained using an alternative WaveCatcher system 7097545 capable of recording up to 1024 samples. The results are not directly comparable to the MC results since they include electronics signal processing.
• Figure 5: Fraction of detected photons in the detector for each end as predicted by the model. Red dots shows photons detected at the sensor closer to the deposition, black squares for the opposite end and green triangles show the sum of both sensor ends.