The NEWS-G Experiment

The New Experiments With Spheres – Gas (NEWS-G) network are a number of experiments working with the novel technology of a spherical proportional counter (SPC). The benefits of such a technology are;

• Cheap and simple technology low threshold
• single read-out (in simplest form)
• flexible gas, gain and pressure
• good energy resolution
• efficient fiducial cuts

For the ideal case of a small spherical sensor located at the centre of a spherical shell, the electric field goes as 1/r² and the capacitance is proportional to the size of the inner sensor so is of order 1 pF. Charges produced in the volume will drift until ~1 mm from the sensor, where an avalanche occurs. This high amplification close the ball minimises the diffusion of the secondary charges and reduces the rise-time of a pulse. This allows single electron detection. The rise-time of pulses may be used to select the fiducial region of the detector.

The applications of such a versatile detector are many, including gamma ray and neutron spectroscopy, coherent nuclear neutrino scattering, double beta-decay searches and Dark Matter (DM) detection. SeDiNe (Spherical Detector of Neutrons) is one such sphere, 60 cm in diameter and made from low activity copper and installed at the Laboratoire Souterrain de Modane (LSM). Initially implemented to investigate the low thermal and fast neutron fluxes in the lab, SeDiNe has also been used to look for low mass dark matter particle candidates, and recently published a new limit for a 0.5 GeV/c² DM candidate. In late 2018 a 1.4 m diameter copper sphere will be installed in SNOLAB in Canada. As the second deepest and the cleanest underground laboratory in the world, SNOLAB offers a shelter from cosmic rays and secondary particles. The main physics aims will be to search for:

• Dark matter candidates with a mass in the range 0.1 GeV/c² to 5 GeV/c² through spin independent couplings
• Kaluza Klein axions through twi photon decay channel
• Dark matter candidates with spin dependent couplings through the selection of gases containing hydrogen

The Particle Physics group at the University of Birmingham is involved in research and development for the next stages of the project as well as simulation studies.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no 841261 (DarkSphere).

Collaborations with colleagues in CEA-Saclay (France) are supported by the Internation Exchanges scheme of The Royal Society.

Interactions with the phenomenology community have been supported in part by the IPPP Associateship programme.