Exploring light dark matter with the DarkSPHERE spherical proportional counter electroformed underground at the Boulby Underground Laboratory
L. Balogh, C. Beaufort, M. Chapellier, E. C. Corcoran, J.-M. Coquillat, A. Dastgheibi-Fard, Yanqing Deng, D. Durnford, C. Garrah, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, Philippe C. Gros, O. Guillaudin, E. W. Hoppe, I. Katsioulas, F. M. Kelly, P. Knights, P. Lautridou, I. Manthos, R.D. Martin, J. Matthews, J.-F. Muraz, T. J. Neep, K. Nikolopoulos, P. O’Brien, M.-C. Piro, N. Rowe, D. Santos, G. Savvidis, I. Savvidis, F. Vazquez de Sola Fernandez, R. J. Ward, E. Banks, L. Hamaide, Christopher McCabe, K. Mimasu, S. Paling
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 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 $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}41}$ $(2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}43})\text{ }\text{ }{\mathrm{cm}}^{2}$ for a dark matter mass of 0.1(1) GeV. The use of a hydrogen-rich gas mixture with a natural abundance of $^{13}\mathrm{C}$ 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 superheavy dark matter with masses around the Planck scale that leave extended ionization tracks in the detector.