Search for exotic neutrino-electron interactions using solar neutrinos in XMASS-I

We have searched for exotic neutrino-electron interactions that could be produced by a neutrino millicharge, by a neutrino magnetic moment, or by dark photons using solar neutrinos in the XMASSI liquid xenon detector. We observed no significant signals in 711 days of data. We obtain an upper limit for neutrino millicharge of 5.4 x 10(-12)e at 90% confidence level assuming all three species of neutrino have common millicharge. We also set flavor-dependent limits assuming the respective neutrino flavor is the only one carrying a millicharge, 7.3 x 10(-12)e for nu(e), 1.1 x 10(-11)e for nu(mu), and 1.1 x 10(-11)e for nu(tau). These limits are the most stringent yet obtained from direct measurements. We also obtain an upper limit for the neutrino magnetic moment of 1.8 x 10(-)(10) Bohr magnetons. In addition, we obtain upper limits for the coupling constant of dark photons in the U(1)(B - L) model of 1.3 x 10(-6) if the dark photon mass is 1 x 10(-3) MeV/c(2), and 8.8 x 10(-5) if it is 10 MeV/c(2). (C) 2020 The Author(s). Published by Elsevier B.V.