Calculating the Cherenkov radiation emitted by low-energy proton in liquid argon (LAr) near UV resonance (~106.6 nm) and comparing with argon scintillation light at 128 nm.*

Neutrino experiments using liquid argon (LAr) detectors estimate the amount of light produced by different types of particles, but only consider scintillation light, at 128 nm, ignoring Cherenkov light contributions. This research aims to theoretically compare these two contributions to the total amount of light produced between ~128 – 500 nm for a proton travelling in LAr and explores how to leverage these under-utilized observables for future detector applications.

A new theoretical fit of the refractive index of LAr was performed using recent experimental data, which incorporates the physics of anomalous dispersion in the UV resonance for the first time.  Using this fit, we integrate the Frank-Tamm formula to calculate the instantaneous Cherenkov angular distribution and yield of a proton with a given kinetic energy, as well as the integrated distribution and yield over its trajectory.  We compare our results with those obtained using two other non-absorptive refractive index fits available in the literature.

Additionally, Cherenkov radiation is highly collimated and emitted instantaneously, whereas scintillation light is isotropic and emitted after a delay. This fundamental difference in their angular distribution (AD) sets the ground for differentiating the Cherenkov signal over the scintillation background, resulting in a substantial observational effect > 4σ for ~500 MeV protons in LAr which suggests collimated Cherenkov measurements for increasing precision in detector applications.