Study of luminescence mechanism by neutral bremsstrahlung in gaseous argon

Secondary scintillation light (S2 signal) has been used in two-phase detectors for searching direct dark matter because of its useful characteristics. In general, electrons extracted from the liquid phase of two-phase detectors produce excimers in the gaseous phase that emit a vacuum ultraviolet (VUV) S2 signal. However, recent research suggests that the S2 signal in argon has another luminescence mechanism called "neutral bremsstrahlung". In this study, detailed measurements of neutral-bremsstrahlung-induced-S2-signal and VUV S2 signal in argon are reported.