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 $<100\mathrm{m}$ leads to a ratio of observed event rate to predicted rate of $0.976\pm 0.024$. With our new flux evaluation, this ratio shifts to $0.943\pm 0.023$, 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-$\nu$ data disfavors the no-oscillation hypothesis at 99.8% C.L. The oscillation parameters are such that $|\Delta m_{\mathrm{new}}^2|>1.5{\mathrm{eV}}^2$ (95%) and ${sin}^2(2{\theta }_{\mathrm{new}})=0.14\pm 0.08$ (95%). Constraints on the ${\theta }_{13}$ neutrino mixing angle are revised. DOI: http://dx.doi.org/10.1103/PhysRevD.83.073006 © 2011 American Physical Society