Cherenkov and scintillation light separation in water-based liquid scintillator with the CHESS experiment

Separate identification of scintillation and Cherenkov light produced in a scintillating medium enables outstanding capabilities for future particle detectors. Water-based liquid scintillator (WbLS), a suspension of liquid scintillator in water, may provide affordable scaling to large-scale, directional, low-threshold detectors. Such a hybrid scintillation/Cherenkov detector would be sensitive to a broad range of physics, from long-baseline neutrino oscillation to low-energy and rare-event searches. The CHESS experiment exploits the fact that Cherenkov light is emitted pico-seconds after the excitation, with a characteristic cone-like topology, while scintillation light is emitted isotropically, typically at nano-second time scales. With an array of small, fast photo-multipliers (PMTs) and state-of-the-art electronics, the CHESS detector achieves sub-nanosecond time resolution. The Cherenkov and scintillation components of light emitted by WbLS are measured by characterizing the photon emission time profile. Here we present for the first time the time profile characterization and Cherenkov/scintillation separation results for a range of WbLS loadings.