Quenching factor measurement of neon nuclei in neon gas and study of the feasibility of detecting coherent elastic neutrino-nucleus scattering at a nuclear reactor using a spherical proportional counter

Abstract

The NEWS-G collaboration uses Spherical Proportional Counters (SPCs) to search for weakly interacting massive particles (WIMPs) through direct detection. Due to their sensitivity to single electrons from ionization, SPCs are also considered for the detection of neutrinos via coherent elastic neutrino-nucleus scattering (CE$\nu$NS). We study the feasibility of an experiment conducted near a nuclear reactor, and provide estimates of the CE$\nu$NS event rate in four different targets, and provide preliminary event rates of backgrounds from materials intrinsic radioactivity. From these calculations, we propose xenon and argon as viable targets for a CE$\nu$NS experiment with SPCs at a nuclear power plant. \ \indent The detection of low-energy nuclear recoils induced by both CE$\nu$NS and WIMPs presents several challenges. One of them is the energy calibration to nuclear recoils in the sub-keV region. We explored the feasibility of measuring the nuclear quenching factor of neon nuclear recoils induced by a neutron beam, produced at the TUNL facility, in an SPC filled with \SI{2}{bar} of Ne+CH$4$ (\SI{3}{%}). A new analysis technique was developed to extract the quenching factor between 0.43 and \SI{11}{keV{nr}}, by implementing a Bayesian analysis framework and simultaneously fitting multiple data sets recorded during the experimental campaign. The energy dependence of the nuclear quenching factor is modelled using a simple power law: $\alpha$E$^{\beta}_{nr}$, whose parameters were measured to be $\alpha$ = 0.2801 $\pm$ 0.0050 (fit) $\pm$ 0.0045 (sys) and $\beta$ = 0.0867 $\pm$ 0.020 (fit) $\pm$ 0.006 (sys). These measurements provide the first estimation of the nuclear quenching factor in neon gas.