First measurement of nuclear recoil head-tail sense in a fiducialised WIMP dark matter detector

TL;DR

This paper reports the first measurement of nuclear recoil head-tail sense in a fiducialised low-pressure TPC detector, demonstrating directional sensitivity for WIMP detection with a novel gas mixture enabling background-free operation.

Contribution

It presents the first detection of nuclear recoil directionality in a fully fiducialised TPC using a CS2 + CF4 + O2 mixture, advancing directional dark matter detection technology.

Findings

Head-tail sensitivity retained after adding oxygen to the gas mixture.

Demonstrated background-free operation at current sensitivities.

Measured recoil track vectors for sulfur, fluorine, and carbon.

Abstract

Recent computational results suggest that directional dark matter detectors have potential to probe for WIMP dark matter particles below the neutrino floor. The DRIFT-IId detector used in this work is a leading directional WIMP search time projection chamber detector. We report the first measurements of the detection of the directional nuclear recoils in a fully fiducialised low-pressure time projection chamber. In this new operational mode, the distance between each event vertex and the readout plane is determined by the measurement of minority carriers produced by adding a small amount of oxygen to the nominal CS$_{2}$ + CF$_{4}$ target gas mixture. The CS$_2$ + CF$_4$ + O$_2$ mixture has been shown to enable background-free operation at current sensitivities. Sulfur, fluorine, and carbon recoils were generated using neutrons emitted from a $^{252}$Cf source positioned at different locations around the detector. Measurement of the relative energy loss along the recoil tracks allowed the track vector sense, or the so-called head-tail asymmetry parameter, to be deduced. Results show that the previously reported observation of head-tail sensitivity in pure CS$_{2}$ is well retained after the addition of oxygen to the gas mixture.