Speaker
Description
Next-generation rare event searches require robust particle identification and background rejection at the MeV scale, driving demand for high-resolution topological imaging. The LiquidO paradigm achieves this by utilizing an opaque monolithic medium to stochastically confine scintillation light, preserving detailed event topology. This localized light is sampled by an embedded lattice of wavelength-shifting fibers, projecting the event structure onto a photosensor array at the detector boundary. To validate the imaging capabilities of this technology, we present results from BPULSE (Berkeley-PennState Universities LiquidO Science Experiment), a benchtop-scale LiquidO prototype.
The BPULSE detector comprises a 4-liter cubic volume of opaque organic scintillator instrumented with an alternating orthogonal fiber lattice coupled to a 64-channel SiPM readout. We characterize the detector utilizing a Compton coincidence technique. By tagging collimated \gamma-rays from $^{137}\text{Cs}$ and $^{60}\text{Co}$ sources scattered into an aperture-restricted external detector, we kinematically constrain the internal recoil electrons. Isolating this narrow phase space of initial electron energies, vertices, and trajectories allows us to systematically map the detector's topological response.
From these measurements, we present the spatial, temporal, and calorimetric response of BPULSE at sub-MeV energies. These measurements are critical for tuning optical transport models and validating advanced reconstruction algorithms (including simulation-based inference approaches like GraphNeT) required for future ton-scale neutrino observatories, such as the proposed CLOUD reactor experiment and the NuDoubt search for $0\nu\beta^+\beta^+$.