Reactor antineutrino anomaly

Abstract

Recently, new reactor antineutrino spectra have been provided for 235 U, 239 Pu, 241 Pu, and 238 U, increasing the mean flux by about 3 percent. To a good approximation, this reevaluation applies to all reactor neutrino experiments. The synthesis of published experiments at reactor-detector distances < 100 m leads to a ratio of observed event rate to predicted rate of 0.976±0.024. With our new flux evaluation, this ratio shifts to 0.943±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 non-standard neutrino state driving neutrino oscillations at short distances is discussed. The combined analysis of reactor data, gallium solar neutrino calibration experiments, and MiniBooNEν data disfavors the no-oscillation hypothesis at 99.8% C.L. The oscillation parameters are such that |∆m 2 new | > 1.5 eV 2 (95%) and sin 2 (2θnew) = 0.14 ± 0.08 (95%). Constraints on the θ13 neutrino mixing angle are revised.

Neutrino phenomenology in a3+1+1framework

“…The GA has been reported in [26] and also discussed clearly in [17] and [55]: SAGE and Gallex have independently measured a lower-than-expected flux of ν e from the decay of megacurie sources of 51 Cr and 37 Ar, corresponding to anomalously low rates of the reaction ν e + 71 Ga→ 71 Ge + e − . This is in principle bounded by similar measurements of the rate of ν e + 12 C → 12 N g.s.…”

“…Reactor and Gallium Anomalies: The RAA is detailed in [17,25] and corresponds to a lower-than-expected flux ofν e emitted from nuclear reactors. The GA has been reported in [26] and also discussed clearly in [17] and [55]: SAGE and Gallex have independently measured a lower-than-expected flux of ν e from the decay of megacurie sources of 51 Cr and 37 Ar, corresponding to anomalously low rates of the reaction ν e + 71 Ga→ 71 Ge + e − .…”

“…The most statistically significant of these position-and energy-independent anomalies is the reactor antineutrino anomaly [17,25] (RAA), where the global average of the observedν e flux is less than anticipated by a factor R RAA = 0.943 ± 0.023. In addition, anomalously low measurements of the ν e scattering gallium cross-section [26], the gallium anomaly (GA), may indicate disappearance of ν e .…”

“…In addition, anomalously low measurements of the ν e scattering gallium cross-section [26], the gallium anomaly (GA), may indicate disappearance of ν e . The deficit based on four measurements of the average ν e scattering cross section from the process ν e + 71 Ga → 71 Ge + e − is, with correlated errors taken to be those in [17], R GA = 0.86 ± 0.06. Independent measurements of the strength of the relevant Gamow-Teller transitions [27] supports the conclusion that this deficit might be due to averaged oscillations of a heavy neutrino.…”

“…Details of how these constraints are combined are given in the appendix. The ν e disappearance constraints include short-baseline reactor experiments with new reactor flux predictions [17] 2 as well as constraints from the ratio of flux observed in the Bugey 40 m and 15 m detectors [18]. Disappearance of ν µ is constrained by CDHS [19] and CCFR [20] at high mass.…”