Charge Amplification in Low Pressure CF4:SF6:He Mixtures with a Multi-Mesh ThGEM for Directional Dark Matter Searches

TL;DR

This study demonstrates that adding helium to low-pressure CF4:SF6 mixtures significantly enhances charge amplification using a Multi-Mesh ThGEM, improving the performance of gaseous TPCs for directional dark matter detection.

Contribution

It presents the first measurements of gas gain and energy resolution in CF4:SF6:He mixtures, showing an order of magnitude increase in charge amplification with helium addition.

Findings

Gas gains of ~10^4 achieved at 100 Torr pressure.

Helium addition improves charge amplification by an order of magnitude.

Mixtures are suitable for low-pressure, directional dark matter detectors.

Abstract

The CYGNO collaboration is developing next generation directional Dark Matter (DM) detection experiments, using gaseous Time Projection Chambers (TPCs), as a robust method for identifying Weakly Interacting Massive Particles (WIMPs) below the Neutrino Fog. SF6 is potentially ideal for this since it provides a high fluorine content, enhancing sensitivity to spin-dependent interactions and, as a Negative Ion Drift (NID) gas, reduces charge diffusion leading to improved positional resolution. CF4, although not a NID gas, has also been identified as a favourable gas target as it provides a scintillation signal which can be used for a complimentary light/charge readout approach. These gases can operate at low pressures to elongate Nuclear Recoil (NR) tracks and facilitate directional measurements. In principle, He could be added to low pressure SF6/CF4 without significant detriment to the length of 16S, 12C, and 19F recoils. This would improve the target mass, sensitivity to lower WIMP masses, and offer the possibility of atmospheric operation; potentially reducing the cost of a containment vessel. In this article, we present gas gain and energy resolution measurements, taken with a Multi-Mesh Thick Gaseous Electron Multiplier (MMThGEM), in low pressure SF6 and CF4:SF6 mixtures following the addition of He. We find that the CF4:SF6:He mixtures tested were able to produce gas gains on the order of 10^4 up to a total pressure of 100 Torr. These results demonstrate an order of magnitude improvement in charge amplification in NID gas mixtures with a He component.