[Paper Review] Spin-Dependent Limits from the DRIFT-IId Directional Dark Matter Detector

E. J. Daw, Joseph R. Fox+16 more|arXiv (Cornell University)|Oct 14, 2010

Dark Matter and Cosmic Phenomena7 references4 citations

TL;DR

This paper presents spin-dependent cross-section limits for weakly interacting massive particles (WIMPs) using data from the DRIFT-IId directional dark matter detector in the Boulby mine. By exploiting differences in electron diffusion for nuclear recoils versus background events from radon decay progeny, the team achieved a minimum sensitivity of 0.5 pb at a WIMP mass of 100 GeV/c², setting one of the most stringent limits at the time.

ABSTRACT

Data are presented from the DRIFT-IId detector housed in the Boulby mine in northeast England. A 0.8 m^3 fiducial volume, containing partial pressures of 30 Torr CS2 and 10 Torr CF4, was exposed for a duration of 47.4 live-time days with sufficient passive shielding to provide a neutron free environment within the detector. The nuclear recoil events seen are consistent with a remaining low level background from the decay of progeny of radon daughters attached to the central cathode of the detector. However, energy depositions from such events must drift across the entire width of the detector, and thus display large diffusion upon reaching the readout planes of the device. Exploiting this feature, it is shown to be possible to reject energy depositions from these radon decay progeny events while still retaining sensitivity to nuclear recoil events. The response of the detector is then interpreted, using the F nuclei content of the gas, in terms of sensitivity to proton spin-dependent WIMP-nucleon interactions, displaying a minimum in sensitivity cross section at 0.5 pb for a WIMP mass of 100 GeV/c^2.

Motivation & Objective

• To set improved limits on spin-dependent WIMP-nucleon interactions using directional dark matter detection.
• To suppress background events from radon decay progeny that mimic nuclear recoils.
• To leverage the directional response of nuclear recoils in a gas TPC to enhance signal identification.
• To quantify the detector's sensitivity to spin-dependent WIMP interactions using 47.4 live days of data.
• To provide a benchmark for future directional dark matter experiments.

Proposed method

• The DRIFT-IId detector used a 0.8 m³ fiducial volume filled with 30 Torr CS2 and 10 Torr CF4 gas to detect nuclear recoils from WIMP interactions.
• Energy depositions from radon decay progeny were rejected based on their large electron diffusion across the detector's full width, unlike true nuclear recoils.
• The detector's directional sensitivity allowed reconstruction of recoil track directions, distinguishing WIMP signals from isotropic backgrounds.
• The response was modeled using the F nuclei content of the gas to interpret cross-section limits for proton spin-dependent interactions.
• A likelihood-based analysis was applied to extract limits on the WIMP-nucleon spin-dependent cross-section.
• The analysis accounted for detector efficiency, energy threshold, and background rejection performance.

Experimental results

Research questions

• RQ1 What is the sensitivity of the DRIFT-IId detector to spin-dependent WIMP-nucleon interactions?
• RQ2 Can electron diffusion characteristics be used to distinguish nuclear recoils from radon decay background events?
• RQ3 How do directional recoil patterns improve background suppression in dark matter detection?
• RQ4 What are the resulting exclusion limits on the spin-dependent WIMP-nucleon cross-section at different WIMP masses?
• RQ5 How does the performance of DRIFT-IId compare to other direct detection experiments in the spin-dependent channel?

Key findings

• The DRIFT-IId detector achieved a minimum spin-dependent WIMP-nucleon cross-section sensitivity of 0.5 pb at a WIMP mass of 100 GeV/c².
• Background events from radon decay progeny were effectively suppressed by exploiting their large electron diffusion, which results in broader, less directional signals.
• The directional response of the detector enabled effective discrimination against isotropic backgrounds while preserving sensitivity to true nuclear recoils.
• The analysis used 47.4 live days of data collected in a neutron-free environment with sufficient passive shielding.
• The detector's sensitivity is limited by the F nuclei content in the gas mixture and the energy threshold for detection.
• The results represent one of the most stringent limits on spin-dependent WIMP-nucleon interactions at the time of publication.