Measurement of Light Yield Response of Gd-compatible Water-based Liquid Scintillator with the Brookhaven 1-ton testbed

TL;DR

This work addresses the challenge of achieving high light yield while preserving Cherenkov information in a gadolinium-loaded WbLS medium. It combines a 1-ton detector study at BNL with benchtop Compton-edge measurements and detailed MC tuning to separate Cherenkov and non-Cherenkov components as WbLS concentration is varied from $0.35\%$ to $1.0\%$. The key findings show LY increasing from $69.16 \pm 6.92$ ph/MeV to $87.32 \pm 8.73$ ph/MeV across the range, with Cherenkov production largely concentration-invariant and re-emission boosting non-Cherenkov light at higher concentrations. The results demonstrate long-term stability at $1.0\%$ and provide a quantitative framework for optimizing future WbLS-based detectors for neutrino physics, including neutron-tagging capabilities via gadolinium.

Abstract

The Water-based Liquid Scintillator (WbLS) enables hybrid detection by combining scintillation and Cherenkov signals, providing superior event reconstruction capabilities compared to conventional neutrino detectors. We measured the light yield of Gd-compatible WbLS at varying concentrations from 0.35\% to 1\% by mass, using cosmic-ray muons in a 1-ton scale detector at BNL. The light yield is measured as (69.16 $\pm$ 6.92) ph / MeV at 0.35\% concentration, which increased to (87.32 $\pm$ 8.73) ph / MeV at 1\%. These results establish a quantitative basis for optimizing future WbLS-based detectors in neutrino physics.

Figures (13)

• Figure 1: (a) Schematic of the 1-ton detector. (b) Photograph of the 1-ton detector installed inside a light-tight dark box.
• Figure 2: Conceptual diagram of the 1-ton WbLS detector showing the distinction between in-ring and out-ring PMT regions. The dashed lines represent the Cherenkov cone emitted by a through going muon, and the solid arrow indicates the muon's path. Out-ring PMTs (blue) primarily detect isotropically emitted non-Cherenkov light (mostly scintillation light), whereas in-ring PMTs (red) are sensitive to both Cherenkov and non-Cherenkov light.
• Figure 3: (a) Two orthogonal layers of hodoscope array. (b) The bottom hodoscope array, positioned below the tank.
• Figure 4: Triggered events time structure showing the first 1,000 ns. The absolute trigger time $t_0$ is at 480. The left peak is majority events. The middle is alpha events. The right is top paddle events. The time structure is primarily due to the contribution from the cable length differences for the alpha and top paddle signals and the intrinsic signal processing delay for the majority signal.
• Figure 5: A typical charge spectrum of alpha events from a single PMT channel. The high-statistics peak near 0 is the pedestal, while the subsequent peak corresponds to the single photoelectron (SPE). The red curve shows a Gaussian fit near the SPE peak and the mean of a Gaussian fit is indicated by the vertical dashed line