Reactor antineutrino anomaly

Abstract

Recently, new reactor antineutrino spectra have been provided for $^{235}\mathrm{U}$, $^{239}\mathrm{Pu}$, $^{241}\mathrm{Pu}$, and $^{238}\mathrm{U}$, increasing the mean flux by about 3%. To a good approximation, this reevaluation applies to all reactor neutrino experiments. The synthesis of published experiments at reactor-detector distances $<100\text{ }\text{ }\mathrm{m}$ leads to a ratio of observed event rate to predicted rate of $0.976\ifmmode\pm\else\textpm\fi{}0.024$. With our new flux evaluation, this ratio shifts to $0.943\ifmmode\pm\else\textpm\fi{}0.023$, leading to a deviation from unity at 98.6% C.L. which we call the reactor antineutrino anomaly. The compatibility of our results with the existence of a fourth nonstandard neutrino state driving neutrino oscillations at short distances is discussed. The combined analysis of reactor data, gallium solar neutrino calibration experiments, and MiniBooNE-$\ensuremath{\nu}$ data disfavors the no-oscillation hypothesis at 99.8% C.L. The oscillation parameters are such that $|\ensuremath{\Delta}{m}_{\mathrm{new}}^{2}|>1.5\text{ }\text{ }{\mathrm{eV}}^{2}$ (95%) and ${sin}^{2}(2{\ensuremath{\theta}}_{\mathrm{new}})=0.14\ifmmode\pm\else\textpm\fi{}0.08$ (95%). Constraints on the ${\ensuremath{\theta}}_{13}$ neutrino mixing angle are revised.