Measurement of ionization yield of low energy ions in low pressure $\mathrm{CF}_{4}$ gas for dark matter searches

TL;DR

The work addresses the uncertainty in ionization yields for low-energy nuclear recoils in gaseous detectors used for directional dark matter searches. It introduces a low-energy ion-beam injection setup at Kanagawa University to inject fluorine ions into CF4 at 0.06 atm and measure ionization with a dedicated proportional wire chamber. The main finding is an ionization yield of $0.45$ at $30$ keV with a moderate energy dependence, consistent with prior COMIMAC measurements and SRIM simulations. This methodology provides a direct, tunable way to calibrate gaseous detectors for dark matter experiments and highlights systematic uncertainties that require further study across ions, gases, and detector geometries.

Abstract

Direction-sensitive direct dark matter search experiments have been conducted using gaseous detectors. In spite of the long history of the study on the energy deposition of charged particles in materials, a full agreement between the measured results and theoretical predictions, especially in a low energy scale, are yet to be achieved. It is thus important to experimentally measure the ionization yields of recoil nuclei for the experiments with gaseous detectors using an ionization charge readout scheme. This study measured the ionization yield using a low-energy ion beam facility at Kanagawa University. The ionization yields for fluorine ions with an energy range of 5 $\sim$ 50 keV were measured using a dedicated proportional wire chamber filled with $\mathrm{CF}_{4}$ gas at 0.06 atm. The low-energy ion injection scheme into a gaseous detector was established and the ionization yield for fluorine ions was obtained to be 0.45 at 30 keV with a moderate dependence on the ion energy.

Figures (8)

• Figure 1: Schematic of the accelerator located at Kanagawa University.
• Figure 2: Schematic of the proportional wire chamber detector (left). Right schematic shows the top view of the detector and the tapered structure of the injection hole in the zoomed image.
• Figure 3: Picture of the proportional wire chamber detector (right-side) connected to the beamline (left-side).
• Figure 4: Energy spectra with an electron-gun for various electron energies.
• Figure 5: Energy spectrum with an $^{55}$Fe source. Measured spectrum (blue histogram) was fitted with a sum function of exponential and gaussian (red line). The energy scale was calibrated by the electron-gun measurements.