First upper limits on neutrino electromagnetic properties from the CONUS experiment

We report first constraints on neutrino electromagnetic properties from neutrino-electron scattering using data obtained from the CONUS germanium detectors, i.e. an upper limit on the effective neutrino magnetic moment and an upper limit on the effective neutrino millicharge. The electron antineutrinos are emitted from the 3.9 GW$_\mathrm{th}$ reactor core of the Brokdorf nuclear power plant in Germany. The CONUS low background detectors are positioned at 17.1 m distance from the reactor core center. The analyzed data set includes 689.1 kg$\cdot$d collected during reactor ON periods and 131.0 kg$\cdot$d collected during reactor OFF periods in the energy range of 2 to 8 keV$_{ee}$. With the current statistics, we are able to determine an upper limit on the effective neutrino magnetic moment $μ_ν< 7.5\cdot10^{-11}\,μ_B$ at 90% confidence level. From this first magnetic moment limit we can derive an upper bound on the neutrino millicharge of $\vert q_ν\vert < 3.3\cdot10^{-12}\,e_0$.