Programme

P.24 -- Posters, VCTP-51

Date: Tuesday, 4 August 2026

Time: 09:30 - 10:30

Optimization of Light Collection in a Miniature Water Cherenkov Detector Using Geant4 Simulations

Hoang Nguyen

IFIRSE, ICISE Centre

Water Cherenkov detectors are widely used in particle and nuclear physics experiments for the detection of charged particles through Cherenkov radiation. Their performance strongly depends on optical photon transport and photon collection efficiency, making the optimization of the optical system a crucial aspect of detector design.In this work, a detailed Geant4 model was developed to study light collection in a planned miniature water Cherenkov detector for cosmic-ray measurements. The proposed detector consists of a $10 \times 10 \times 10\text{ cm}^3$ acrylic water tank instrumented with 16 silicon photomultipliers (SiPMs), Tyvek reflectors, and a cosmic-ray muon coincidence trigger provided by two plastic scintillation counters positioned above and below the detector. The simulation accounts for Cherenkov photon production, optical photon transport, reflections from Tyvek surfaces, and photon collection at the SiPM array.Several optical design parameters were systematically investigated, including SiPM placement, acrylic thickness, Tyvek reflector configuration, and optical coupling conditions (air-gap vs. optical gel). Truth-level simulation data was utilized to evaluate photon collection efficiency, identify optical loss mechanisms, and separate water-generated Cherenkov photons from scintillation noise produced within the acrylic walls.The simulation demonstrates that optical gel coupling significantly suppresses total internal reflection (TIR) at the boundaries, increasing the pure photon yield by a factor of roughly $2.2$ compared to the air-gap configuration. However, this index matching also introduces a trade-off, elevating the material noise fraction (acrylic scintillation) from $\sim 2.5\%$ to approximately $15.6\%$. Furthermore, positioning the Tyvek reflector on the outer surface of the tank enhances the overall photon yield by recovering light trapped in the acrylic walls. Crucially, timing analysis indicates that these acrylic-born photons introduce negligible time dispersion relative to the primary signal from water.These quantitative results provide key baselines for optimizing the detector design, highlighting the trade-offs between signal yield and noise, and support the development of compact SiPM-based water Cherenkov detectors for future applications.

Presenter: Nguyen Hoang