It is established from astronomical and cosmological observations that 85% of the matter content of the universe is in an as of yet unknown form called Dark Matter.  Elucidating the nature of DM is a key priority that would involve discovering unknown fundamental physics and is essential for understanding the structure and evolution of the universe. Although the particle nature of DM is currently unknown, many theories predict that DM consists of stable neutral particles with mass ranging from a few eV to multi-TeV and small, non-zero, couplings to the SM. In the past decades, the scrutiny fell on DM candidates with masses in the 10 GeV to 1 TeV range, however, more recent considerations have brought to attention candidates with lighter masses. 

The spherical proportional counter, is a novel gaseous detector with characteristics that make it ideal for light dark matter searches. These include: a) operating the detector with light gas mixtures naturally maximises the recoil energy; b) extremely low energy threshold, down to a single ionisation electron, thanks to small detector capacitance; c) naturally scalable, through construction of larger vessels and operation at high gas pressures; d) flexible target swapping, which enables background estimation and confirmation of potential signals; e) small number of readout channels; and f) background rejection and detector fiducialisation, through pulse shape analysis and track reconstruction.

The studentship will combine the expertise of Birmingham and Boulby in particle detectors and radiopurity techniques by focusing on the electroformation of detectors for rare event searches. Electroformed spherical proportional counters for light DM searches will be used as the case study, and a prototype detector will be delivered. The student will exploit the newly created electroforming facility at Boulby, which is being developed to give a world-class capability, to produce a sample tray for Boulby’s low background alpha-particle spectrometer, thus enhancing the capabilities of the laboratory’s radio-assay facility. As a result, they will acquire hands-on expertise in high-value state-of-the-art radiopurity and electroformation techniques. Subsequently, this expertise will be used to electroform a spherical proportional counter, which they will instrument and characterise underground at Boulby. An important aspect of this will be the measurement of the detector background. The spherical proportional counter, will be equipped with a multi-anode readout sensor, that the student will design, construct, and characterise at Birmingham prior to installation at Boulby. Data will be recorded using a low cost purified water-based shield. Thus, the project will culminate in the preliminary study of the sensitivity of the detector to light DM. It is expected that such a prototype detector could have world-leading sensitivity to spin-dependent proton-DM interactions. 

This project will be realised within the NEWS-G Collaboration, searching for light DM using spherical proportional counters. NEWS-G is an international collaboration of more than 40 researchers from 10 institutes. Throughout this effort, the student will benefit from discussions and direct collaboration with our international partners. The work will take place initially at Birmingham and subsequently at the Boulby Underground Laboratory.