The Reactor Antineutrino Anomaly

Abstract

Early 2011 new reactor antineutrino spectra have been provided for 235U, 239Pu, 241Pu, and 238U, increasing the mean flux by about 3 percent. The authors reevaluated the ratio of observed event rate to predicted rate of 19 published experiments at reactor-detector distances below 100 m, found to be 0.943 ± 0.023. The deviation from unity, significant at 98.6% C.L., is now being refered as 'the reactor antineutrino anomaly'. The compatibility of our results with the existence of a fourth non-standard neutrino state driving neutrino oscillations at short distances is discussed. The combined analysis of reactor data, gallium solar neutrino calibration experiments data disfavors the no-oscillation hypothesis at 99.8% C.L. The oscillation parameters are such that |Δm new2| > 1.5 eV2 (95%) and sin 2(2θnew) = 0.14 ± 0.08 (95%).