Surface background suppression in liquid argon dark matter detectors using a newly discovered time component of tetraphenyl-butadiene scintillation

Abstract

Decays of radioisotopes on inner detector surfaces can pose a major background concern for the direct detection of dark matter. While these backgrounds are conventionally mitigated with position cuts, these cuts reduce the exposure of the detector by decreasing the sensitive mass, and uncertainty in position determination may make it impossible to adequately remove such events in certain detectors. In this paper, we provide a new technique for substantially reducing these surface backgrounds in liquid argon (LAr) detectors, independent of position cuts. These detectors typically use a coating of tetraphenyl-butadiene (TPB) on the inner surfaces as a wavelength shifter to convert vacuum ultraviolet (VUV) LAr scintillation light to the visible spectrum. We find that TPB scintillation contains a component with a previously unreported exceptionally long lifetime ($\sim$ms). We discovered that this component differs significantly in magnitude between alpha, beta, and VUV excitation, which enables the use of pulse shape discrimination to suppress surface backgrounds by more than a factor of $10^3$ with negligible loss of dark matter sensitivity. We also discuss how this technique can be extended beyond just LAr experiments.

References in corpus (3)

• Low-Mass Dark Matter Search with the DarkSide-50 Experiment
• First Results from the DarkSide-50 Dark Matter Experiment at Laboratori Nazionali del Gran Sasso
• Evidence of delayed light emission of TetraPhenyl Butadiene excited by liquid Argon scintillation light

Cited by in corpus (10)

• DarkSide-50 532-day Dark Matter Search with Low-Radioactivity Argon
• Search for dark matter with a 231-day exposure of liquid argon using DEAP-3600 at SNOLAB
• Wavelength shifters for applications in liquid argon detectors
• Pulseshape discrimination against low-energy Ar-39 beta decays in liquid argon with 4.5 tonne-years of DEAP-3600 data
• The liquid-argon scintillation pulseshape in DEAP-3600
• Sensitivity projections for a dual-phase argon TPC optimized for light dark matter searches through the ionization channel
• The science and technology of liquid argon detectors
• Development and characterization of a slow wavelength shifting coating for background rejection in liquid argon detectors
• Technique for Surface Background Rejection in Liquid Argon Dark Matter Detectors using Layered Wavelength-Shifting and Scintillating Thin Films
• Surface background rejection technique for liquid argon dark matter detectors using a thin scintillating layer