[Paper Review] Direction-sensitive dark matter search with a low-background gaseous detector NEWAGE-0.3b''

Tomonori Ikeda, Kiseki Nakamura+15 more|arXiv (Cornell University)|Jan 25, 2021

Dark Matter and Cosmic Phenomena35 references10 citations

TL;DR

This paper presents the first directional dark matter search using a low-background gaseous time projection chamber (NEWAGE-0.3b") equipped with a low-alpha-ray emission rate micro-pixel chamber (LAµ-PIC). The experiment achieved a 90% confidence level upper limit of 50 pb on the spin-dependent WIMP-proton cross section for 100 GeV/c² WIMPs—setting the most stringent directional constraint to date.

ABSTRACT

NEWAGE is a direction-sensitive dark matter search using a low-pressure gaseous time projection chamber. A low alpha-ray emission rate micro pixel chamber had been developed in order to reduce background for dark matter search. We conducted the dark matter search at the Kamioka Observatory in 2018. The total live time was 107.6 days corresponding to an exposure of 1.1 kg${\cdot}$days. Two events remained in the energy region of 50-60 keV which was consistent with 2.5 events of the expected background. A directional analysis was carried out and no significant forward-backward asymmetry derived from the WIMP-nucleus elastic scatterings was found. Thus a 90% confidence level upper limit on Spin-Dependent WIMP-proton cross section of 50 pb for a WIMP mass of 100 GeV/c2 was derived. This limit is the most stringent yet obtained from direction-sensitive dark matter search experiments.

Motivation & Objective

• To develop a low-background, direction-sensitive dark matter detector using a novel LAµ-PIC with reduced alpha-ray emission.
• To perform a directional dark matter search in the Kamioka Observatory with improved background suppression.
• To set a new, stringent upper limit on the spin-dependent WIMP-proton cross section using directional analysis.
• To validate the effectiveness of radiopure materials and advanced tracking in reducing surface and environmental backgrounds.

Proposed method

• Employed a low-pressure gaseous micro time projection chamber (µTPC) with CF4 gas at 76 Torr for enhanced spin-dependent WIMP-nucleus scattering detection.
• Utilized a newly developed LAµ-PIC with epoxy/polyimide surface instead of glass cloth to reduce U/Th contamination by a factor of 100.
• Integrated a gas electron multiplier (GEM) for stable signal amplification and a TPC field cage for uniform electric field.
• Applied a 100 MHz FPGA-based readout system to record hit-patterns and time-over-threshold (TOT) for 3D track reconstruction.
• Used waveform digitizers to measure energy deposition from charge signals, enabling precise energy calibration.
• Implemented directional analysis via forward-backward asymmetry in nuclear recoil angular distribution to identify WIMP signals.

Experimental results

Research questions

• RQ1 Can a low-background LAµ-PIC significantly reduce surface alpha-ray backgrounds in directional dark matter searches?
• RQ2 Does the directional analysis of nuclear recoil tracks in a µTPC provide a detectable forward-backward asymmetry consistent with WIMP-nucleus scattering?
• RQ3 What is the ultimate sensitivity of a direction-sensitive dark matter experiment using a low-pressure gaseous TPC with radiopure components?
• RQ4 How do ambient gamma-rays, neutrons, and residual radon contribute to the background in the 50–60 keV energy window?
• RQ5 Can z-coordinate fiducialization in a negative-ion gas TPC further suppress surface backgrounds?

Key findings

• The NEWAGE-0.3b" detector achieved a total exposure of 1.1 kg·days over 107.6 days of live time at the Kamioka Observatory.
• Only two events were observed in the 50–60 keV energy window, consistent with the expected 2.5 background events.
• No significant forward-backward asymmetry was found, indicating no evidence of directional WIMP signal.
• A 90% confidence level upper limit of 50 pb was set on the spin-dependent WIMP-proton cross section for a 100 GeV/c² WIMP mass.
• This limit improves upon the previous best directional constraint by a factor of 15, marking the most stringent directional dark matter limit to date.
• Background contributions were dominated by ambient gamma-rays and neutrons, with residual surface alpha-rays from the LAµ-PIC contributing less than 1.2×10⁻¹ events in the signal window.