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In a dark tank holding thirty tons of water, the liquid glows when a ghostly particle streaks through. Neutrinos barely interact with matter, but occasionally they bump into atoms, and a flash is born. To catch it, a special substance, a liquid scintillator, is added to the water to amplify the light.

Ordinary detectors see either one type of glow or the other. Here, both are mixed: Cherenkov radiation (a bluish cone, like a sonic boom from a supersonic jet, but from a particle moving faster than light in water) and scintillation light (a soft, uniform glow). The ratio can be adjusted right in the tank, tuning the detector for different tasks.

Why bother? Neutrinos come from the Sun, from stellar explosions, and from nuclear reactors. Some are fast and energetic, others slow and feeble. One tank with tunable liquid can catch both kinds, and also tell them apart from random noise. Scientists have already launched a prototype at Brookhaven Laboratory and are gearing up to analyze the first data.

Original abstract

as written by the authors arXiv:2603.20019

Water-based Liquid Scintillator (WbLS) was proposed over a decade ago as a novel detector medium that might allow the separation and tuning of the relative ratio of the Cherenkov and Scintillation signals. A detector deploying this technology could combine GeV-scale and MeV-scale neutrino detection at scale. Furthermore, the metal-loading capability of such a material enables neutron tagging and allows the effective particle containment to be tuned. WbLS is attractive both for the potential to use it in large detectors and the ability to modify the configuration in situ. At Brookhaven National Laboratory (BNL), two prototypes have been built for understanding WbLS properties and stability, with masses of 1-ton and 30-ton, respectively. We present here the 30-ton prototype detector design, installation, and operation. Results from the analysis of data collected in the two detectors will follow in future publications.