A borehole muon detector with SiPM-on-tile technology

We developed a compact and rugged muon detector designed for deployment in boreholes. The detector uses a SiPM-on-tile approach in which silicon photomultipliers are directly coupled to scintillator tiles, thereby eliminating the need for wavelength-shifting fibers and long scintillator bars. The modular design is based on a 64-channel unit, 140~cm in length and 80~mm in diameter, composed of 5 × 5~cm² scintillator tiles coupled to SiPMs, powered and read out using off-the-shelf electronics. The detector has an average muon detection efficiency above 95% and acceptance over 5^∘--60^∘ in zenith and 0^∘--360^∘ in azimuth. Simulations indicate that reconstruction combining hit positions and energy deposits achieves a zenith resolution of 1.5--4.0^∘ across most of the zenith range. This work demonstrates a compact, rugged, and cost-effective borehole muon detector based on the SiPM-on-tile approach, offering a new alternative for muon tomography.