Cherenkov and Scintillation in an optical LAr neutrino detector

The continued use and development of liquid argon, liquid scintillator, and water Cherenkov detectors can be leveraged to construct highly capable and well understood detectors sensitive to a diverse range of physics. In particular, ongoing efforts to distinguish Cherenkov and scintillation photons in organic liquid scintillators (LS) can be more directly achieved in liquid argon (LAr). In contrast to LS, LAr scintillates narrowly around 128 nm, leaving the broad Cherenkov spectrum uncontaminated above this wavelength. These Cherenkov photons are readily detected by common devices such as PMTs while the scintillation photons can be detected with the same devices upon coating with a wavelength shifter like PTP or TPB. From a simulation of a 50/50 distribution of TPB-coated/uncoated PMTs, the number of Cherenkov photons detected with high purity by only uncoated PMTs can be as high as modern water Cherenkov detectors and the number of scintillation photons detected can be as high as modern LS detectors, contributing roughly 3% (0.5%) to the energy resolution at 1 (50) MeV.

This type of detector would provide the same particle interaction channels as a LAr TPC and use largely established event analysis techniques from scintillator and Cherenkov detectors, augmenting planned measurements of the neutrino mass ordering and CP phase. The high scintillation yield provides good resolution and a low threshold, enhancing access to the wealth of physics at lower energies: solar, supernovae, relic supernovae, etc. Cherenkov imaging provides high-energy event reconstruction and together with scintillation offers new or improved capabilities for PID and signal-background separation. Further valuable measurements should also be possible, like a search for neutrinoless double beta decay of ¹³⁶Xe doped into the LAr.