Exploring light dark matter with the DarkSPHERE spherical proportional counter electroformed underground at the Boulby Underground Laboratory

TL;DR

DarkSPHERE is a proposed underground spherical proportional counter designed to detect light dark matter particles in the 0.05-10 GeV range, with ultra-low background and sensitivity to various dark matter interactions.

Contribution

This paper introduces the conceptual design of DarkSPHERE, a novel underground detector with advanced background suppression and broad dark matter detection capabilities.

Findings

Background level below 0.01 dru achieved

Sensitivity to spin-independent cross-section of 2x10^-41 to 2x10^-43 cm^2

Enhanced sensitivity to spin-dependent interactions for light dark matter

Abstract

We present the conceptual design and the physics potential of DarkSPHERE, a proposed 3 m in diameter spherical proportional counter electroformed underground at the Boulby Underground Laboratory. This effort builds on the R&D performed and experience acquired by the NEWS-G Collaboration. DarkSPHERE is primarily designed to search for nuclear recoils from light dark matter in the 0.05--10 GeV mass range. Electroforming the spherical shell and the implementation of a shield based on pure water ensures a background level below 0.01 dru. These, combined with the proposed helium-isobutane gas mixture, will provide sensitivity to the spin-independent nucleon cross-section of $2\times 10^{-41} (2\times 10^{-43})$ cm$^2$ for a dark matter mass of $0.1 (1)$ GeV. The use of a hydrogen-rich gas mixture with a natural abundance of $^{13}$C provides sensitivity to spin-dependent nucleon cross-sections more than two orders of magnitude below existing constraints for dark matter lighter than 1 GeV. The characteristics of the detector also make it suitable for searches of other dark matter signatures, including scattering of MeV-scale dark matter with electrons, and super-heavy dark matter with masses around the Planck scale that leave extended ionisation tracks in the detector.