S. Westerdale

Scintillation Efficiency Measurement of Na Recoils in NaI(Tl) Below the DAMA/LIBRA Energy Threshold

The dark matter interpretation of the DAMA modulation signal depends on the NaI(Tl) scintillation efficiency of nuclear recoils. Previous measurements for Na recoils have large discrepancies, especially in the DAMA/LIBRA modulation energy region. We report a quenching effect measurement of Na recoils in NaI(Tl) from 3keV

Radiogenic neutron yield calculations for low-background experiments

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A study of nuclear recoil backgrounds in dark matter detectors

to 52keV

A Prototype Neutron Veto for Dark Matter Detectors

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First measurement of surface nuclear recoil background for argon dark matter searches

, covering the whole DAMA/LIBRA energy region for light WIMP interpretations. By using a low-energy, pulsed neutron beam, a double time-of-flight technique, and pulse-shape discrimination methods, we obtained the most accurate measurement of this kind for NaI(Tl) to date. The results differ significantly from the DAMA reported values at low energies, but fall between the other previous measurements. We present the implications of the new quenching results for the dark matter interpretation of the DAMA modulation signal.

Quenching measurements and modeling of a boron-loaded organic liquid scintillator

Abstract Nuclear recoil backgrounds are one of the most dangerous backgrounds for many dark matter experiments. A primary source of nuclear recoils is radiogenic neutrons produced in the detector material itself. These neutrons result from fission and ( α , n ) reactions originating from uranium and thorium contamination. In this paper, we discuss neutron yields from these sources. We compile a list of ( α , n ) yields for many materials common in low-background detectors, calculated using NeuCBOT (Neutron Calculator Based On TALYS ), a new tool introduced in this paper, available at https://github.com/shawest/neucbot . These calculations are compared to computations made using data compilations and SOURCES-4C .

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

Despite the great success of the Standard Model of particle physics, a preponderance of astrophysical evidence suggests that it cannot explain most of the matter in the universe. This so-called dark matter has eluded direct detection, though many theoretical extensions to the Standard Model predict the existence of particles with a mass on the 1–1000 GeV scale that interact only via the weak nuclear force. Particles in this class are referred to as Weakly Interacting Massive Particles (WIMPs), and their high masses and low scattering cross sections make them viable dark matter candidates. The rarity of WIMP-nucleus interactions makes them challenging to detect: any background can mask the signal they produce. Background rejection is therefore a major problem in dark matter detection. Many experiments greatly reduce their backgrounds by employing techniques to reject electron recoils. However, nuclear recoil backgrounds, which produce signals similar to what we expect from WIMPs, remain problematic. There are two primary sources of such backgrounds: surface backgrounds and neutron recoils. Surface backgrounds result from radioactivity on the inner surfaces of the detector sending recoiling nuclei into the detector. These backgrounds can be removed with fiducial cuts, at some cost to the experiment’s exposure. In this dissertation we briefly discuss a novel technique for rejecting these events based on signals they make in the wavelength shifter coating on the inner surfaces of some detectors. Neutron recoils result from neutrons scattering off of nuclei in the detector. These backgrounds may produce a signal identical to what we expect from WIMPs and are extensively discussed here. We additionally present a new tool for calculating (α, n) yields in various materials.

measurement of Na recoils in NaI(Tl) below the DAMA/LIBRA energy threshold

Abstract Neutrons are a particularly dangerous background for direct WIMP dark matter searches; their nuclear recoils with the target nuclei are often indistinguishable from nuclear recoils produced by WIMP-nuclear collisions. In this study, we explore the concept of a liquid scintillator neutron veto detector that would allow direct dark matter detectors to potentially reject neutrons with greater than 99% efficiency. Here we outline the construction and testing of a small prototype detector and the potential implications of this technology for future dark matter detectors.

Efficiency Studies and Simulations of a Neutron Background Veto for Dark Matter Detectors

One major background in direct searches for weakly interacting massive particles (WIMPs) comes from the deposition of radon progeny on detector surfaces. A dangerous surface background is the

Study of Light Collection Efficiency for a Neutron Veto for the DarkSide-50 Dark Matter Detector

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