Study of nuclear recoils in liquid argon with monoenergetic neutrons

Abstract

For the development of liquid argon dark matter detectors we assembled a setup in the laboratory to scatter neutrons on a small liquid argon target. The neutrons are produced mono-energetically (E kin =2.45 MeV) by nuclear fusion in a deuterium plasma and are collimated onto a 3" liquid argon cell operating in single-phase mode (zero electric field). Organic liquid scintillators are used to tag scattered neutrons and to provide a time-of-flight measurement. The setup is designed to study light pulse shapes and scintillation yields from nuclear and electronic recoils as well as from α-particles at working points relevant to dark matter searches. Liquid argon offers the possibility to scrutinise scintillation yields in noble liquids with respect to the populations of the two fundamental excimer states. Here we present experimental methods and first results from recent data towards such studies.

Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy β and nuclear recoils in liquid argon with DEAP-1

“…This upturn has been seen in many experiments [4,19,38] and the cause may not be the same each time. We for example note that the measurement in [38] shows an essentially flat mean F prompt in the energy range considered in this work, as assumed in our model. It is likely that the mean F prompt for electromagnetic events truly increases toward lower energies due to the underlying scintillation physics, at energies below what is considered in this work.…”

“…Model extrapolation for DEAP-3600 Figure 35: Leakage estimation at 120 to 240 PE for a detector with 255 PMTs and 8 PE/keVee light yield (15-30 keVee energy window). The underlying energy spectrum is that of the 39 Ar beta decay, PE counting is assumed to be accurate, and the energy dependence of the mean of the Fprompt distribution is taken from [38]. The solid line shows the analytic model without SPE or electronics noise, and the dotted line has the same SPE noise as the DEAP-1 measurement, but electronics noise per PMT is reduced to account for better read-out electronics and then scaled up to 255 PMTs.…”

“…the prompt and late-PE offsets are zero. To conservatively include a possible upturn in the true mean of the F prompt distribution at lower energies, we implemented the energy dependence of mean F prompt as observed in [38]. The leakage is calculated for the following cases: (a) assuming that SPE identification and counting analysis will make the electronics and SPE noise negligible, (b) using a simple DEAP-1 style charge division method for SPE calibration, i.e.…”

A G/NARRLI Effort. Measuring the Ionization Yield of Low-Energy Nuclear Recoils in Liquid Argon

“…Most of these experiments have used fusion (D-D and D-T) neutrons to induce nuclear recoils within the LAr target volume [20,63,39,52]. In [5] a pulsed 7 Li(p,n) 7 Be neutron source was used to produce high-energy neutrons (604-1600 keV) to induce nuclear recoils in the LAr target volume.…”

“…In [5] a pulsed 7 Li(p,n) 7 Be neutron source was used to produce high-energy neutrons (604-1600 keV) to induce nuclear recoils in the LAr target volume. To probe lower energy nuclear recoils [63,39,52,5] used liquid scintillation detectors placed at known scattering angles to tag the scattered neutrons, allowing kinematic reconstruction of the nuclei recoil energy. To date, the lowest energy nuclear recoils observed were at 10.8 keV using scintillation light [5].…”