Scintillation Properties of a Stilbene Crystal for Low-Mass Dark Matter Searches

Abstract

Direct searches for low-mass WIMPs require sensitivity to low-energy nuclear recoils. Hydrogen-containing targets offer favorable scattering kinematics because low-mass WIMPs can transfer a larger fraction of their kinetic energy to hydrogen nuclei than to heavier nuclei. Trans-stilbene (t-stilbene) is a hydrogen-rich organic crystal that combines this kinematic advantage with efficient scintillation and pulse-shape discrimination (PSD).In this work, we characterize the scintillation decay behavior and effective light yield of a solution-grown t-stilbene crystal to evaluate its suitability for dark matter detection. The detector consists of a cylindrical crystal approximately 1.1 cm in diameter and 1.1 cm in length, optically coupled at opposite ends to two Hamamatsu R12669 photomultiplier tubes. The scintillation waveforms are described by a triple-exponential decay model, yielding fraction-weighted decay time constants of $8.3\pm 0.2$ ns (fast), $20.1\pm 0.3$ ns (medium), and $74.2\pm 1.1$ ns (slow). The effective light yield, determined using a 59.54 keV $\gamma$ ray from an ${}^{241}$Am source, is $3.37\pm 0.02$ photoelectrons per keV.These measurements establish the baseline performance of the detector and support further evaluation of t-stilbene as a target material for rare-event and low-mass dark matter searches.