# Precision laser-based measurements of the single electron response of SPCs for the NEWS-G light dark matter search experiment

## TL;DR

This paper presents a highly precise characterization of the single electron response of spherical proportional counters (SPCs) using a UV-laser system, crucial for low-mass dark matter detection in the NEWS-G experiment.

## Contribution

It introduces a novel calibration method for SPCs, enabling detailed monitoring and measurement of detector response and electron drift properties at unprecedented precision.

## Key findings

- Measured mean ionization energy of 27.6 eV for 2.8 keV X-rays.
- Demonstrated feasibility of sub-keV energy measurements for future gas mixtures.
- Outlined applications for detector monitoring and threshold efficiency measurement.

## Abstract

Spherical Proportional Counters (SPCs) are a novel gaseous detector technology employed by the NEWS-G low-mass dark matter search experiment for their high sensitivity to single electrons from ionization. In this paper, we report on the first characterization of the single electron response of SPCs with unprecedented precision, using a UV-laser calibration system. The experimental approach and analysis methodology are presented along with various direct applications for the upcoming next phase of the experiment at SNOLAB. These include the continuous monitoring of the detector response and electron drift properties during dark matter search runs, as well as the experimental measurement of the trigger threshold efficiency. We measure a mean ionization energy of $\mathrm{W}=27.6\pm0.2~\mathrm{eV}$ in $\mathrm{Ne + CH_4}$ $(2\%)$ for 2.8 keV X-rays, and demonstrate the feasibility of performing similar precision measurements at sub-keV energies for future gas mixtures to be used for dark matter searches at SNOLAB.