New constraint on neutrino magnetic moment and neutrino millicharge from LUX-ZEPLIN dark matter search results

Abstract

Elastic neutrino-electron scattering represents a powerful tool to investigate key neutrino properties. In view of the recent results released by the LUX-ZEPLIN collaboration, we provide a first determination of the limits achievable on the neutrino magnetic moment and neutrino millicharge, whose effect becomes non-negligible in some beyond the Standard Model theories. In this context, we evaluate and discuss the impact of different approximations to describe the neutrino interaction with atomic electrons. The new LUX-ZEPLIN data allows us to set a very competitive limit on the neutrino magnetic moment when compared to the other laboratory bounds, namely $\mu_{\nu}^{\rm{eff}} < 1.1 \times 10^{-11} \, \mu_{\text{B}}$ at 90$\%$ C.L., which improves by a factor of 2.5 the Borexino collaboration limit and represents the second best world limit after the recent XENONnT result. Moreover, exploiting the so-called equivalent photon approximation, we obtain the most stringent limit on the neutrino millicharge, namely $|q_{\nu}^{\rm{eff}}| < 1.5 \times 10^{-13} e_0$ at 90$\%$ C.L., which represents a great improvement with respect to the previous laboratory bounds.