Speaker
Description
The PandaX-20T experiment, a next-generation multi-ton liquid xenon TPC at the China Jinping Underground Laboratory, aims to achieve unprecedented sensitivity for direct dark matter detection. As experiments approach the neutrino-floor regime, efficient suppression of neutron and gamma-induced backgrounds becomes increasingly important. An active Cold Liquid Scintillator (CLS) veto surrounding the xenon target offers a promising approach for enhancing background discrimination, with the additional benefit of reducing thermal gradients and potentially enabling a thinner liquid-xenon cryostat.
We report R&D results from a ~1 L CLS prototype operated down to −100°C,
employing wavelength-shifting optical fibers coupled to silicon photomultipliers (SiPMs) for scintillation readout under cryogenic conditions. The system demonstrates stable operation, with a ~59% reduction in photoelectron yield at −20 °C relative to room temperature. Independent LED calibration measurements confirm reliable SiPM performance at −100 °C, with an observed gain increase of about a factor of two. Geant4 simulations are employed to model optical photon transport, optimize detector geometry, and evaluate neutron and gamma veto performance. These combined studies provide essential input for the design of a large-scale cryogenic scintillator veto for PandaX-20T and demonstrate its potential to significantly enhance background rejection in rare-event searches. Future work will focus on detailed characterization at −100 °C and quantification of neutron-tagging efficiency.
