Dark Matter (DM) constitutes 85% of the matter in the Universe, but what is it made of? This is the most compelling question in physics for over a century. Astrophysical observations and cosmological constraints point towards particle dark matter, which is "cold", long-lived, and electrically neutral. Weakly Interacting Massive Particles (WIMPs) in the mass range between 10 - 1000 GeV have been the main focus of experimental scrutiny. However, lack of conclusive evidence calls for a broadening of our approach to the DM question: Modern theories may explain the observed DM abundance with light dark matter candidates. The current generation of state-of-the-art dark matter detectors, optimised for WIMPs, are not sensitive to such light DM candidates.
DarkSphere aims to shed new light on DM through a novel direct search of unprecedented sensitivity for light DM candidates in the 0.05-10 GeV mass region. The primary tool to achieve this goal is the Spherical Proportional Counter (SPC), a novel gaseous detector. The detector combines large volume with a low energy threshold down to a single electron; a unique feature among DM detectors. It will be filled with light (helium, neon) and hydrogen-rich gases (alkanes) to optimise projectile-target momentum transfer. The NEWS-G collaboration develops and operates SPCs across the globe for light DM searches, installed at the deep-underground laboratories of SNOLAB (Canada), LSM (France) and Boulby (UK).
The goals of DarkSphere are achieved through its mains objectives:
-The study of detector properties, such as the gain, ionisation statistics, and drift time of ions, as well as the production of a detailed simulation framework to reproduce the measured detector properties in order to support measurements and physics analysis.
-The estimation of the ionisation quenching factor - the parameter used to measure the relative ionisation yield of nuclear recoils and electrons - and to study the Migdal effect, both being critical parameters for recoil ionisation modelling.
-The development of a method for fast neutron spectroscopy to study neutron-induced background in rare-event search experiments.
-The discovery or placing stringent constraints on light DM through physics analysis of NEWS-G data, including signal/background discrimination, background estimation, statistical analysis, and phenomenological result interpretation.
