Axial-vector neutral-current measurements in coherent elastic neutrino-nucleus scattering experiments

Abstract

Coherent elastic neutrino-nucleus scattering (CE$ν$NS) is predominantly governed by vector neutral-current interactions, with subleading contributions arising from the axial current in nuclei with non-zero ground-state spin. Experimentally, the extraction of axial-current contributions has been so far of little interest, mainly because of the challenges its measurement entail. In this work, we investigate the relative size of the vector and axial components for target materials currently employed by the neutrino and dark matter experimental communities. We identify fluorine-based compounds as the most promising targets for probing the axial-current event rate. Among them, octafluoropropane ($\text{C}_3\text{F}_8$) emerges as a particularly suitable candidate, given its widespread use in spin-dependent dark matter searches and its relevance for upcoming dedicated CE$ν$NS experiments. Considering both pion decay-at-rest and reactor neutrino fluxes, we show that such measurements can allow an indirect determination of the axial coupling at the $\sim 10\%$ level, depending on flux uncertainties and detector thresholds. We further emphasize that measurements of the axial current will allow to probe spin-dependent new physics scenarios through CE$ν$NS.

Figures (3)

• Figure 1: Expected vector event rates in heavy target materials (left panel) and the corresponding axial-current contributions (right panel), see the text for details.
• Figure 2: Left graph: Total expected event rate as a function of nuclear recoil energy assuming a spallation-source neutrino flux, for a $\text{C}_3\text{F}_8$ detector. Following ESS expectations Baxter:2019mcx, a recoil-energy threshold of 2 keV is adopted. Right graph: Same as the left graph, but for reactor electron antineutrinos. Experimental specifications are taken from the latest CONUS+ run Ackermann:2025obx (see text for details).
• Figure 3: Upper panel: Projected sensitivities to $g_A$, shown as reduced $\chi^2$ profiles, for a spallation-source experiment assuming a $\text{C}_3\text{F}_8$ detector with fiducial masses of 50 kg (left) and 350 kg (right), a 20 m baseline, and different recoil-energy thresholds and neutrino flux uncertainties. Lower panel: Same as the upper panel, but assuming a neutrino flux from a nuclear reactor.