Abstract
We discuss the possibility to explain the anomalies in short-baseline neutrino oscillation experiments in terms of sterile neutrinos. We work in a 3 + 1 framework and pay special attention to recent new data from reactor experiments, IceCube and MINOS+. We find that results from the DANSS and NEOS reactor experiments support the sterile neutrino explanation of the reactor anomaly, based on an analysis that relies solely on the relative comparison of measured reactor spectra. Global data from the νe disappearance channel favour sterile neutrino oscillations at the 3σ level with Δm412 ≈ 1.3 eV2 and |Ue4| ≈ 0.1, even without any assumptions on predicted reactor fluxes. In contrast, the anomalies in the νe appearance channel (dominated by LSND) are in strong tension with improved bounds on νμ disappearance, mostly driven by MINOS+ and IceCube. Under the sterile neutrino oscillation hypothesis, the p-value for those data sets being consistent is less than 2.6 × 10−6. Therefore, an explanation of the LSND anomaly in terms of sterile neutrino oscillations in the 3 + 1 scenario is excluded at the 4.7σ level. This result is robust with respect to variations in the analysis and used data, in particular it depends neither on the theoretically predicted reactor neutrino fluxes, nor on constraints from any single experiment. Irrespective of the anomalies, we provide updated constraints on the allowed mixing strengths |Uα4| (α = e, μ, τ ) of active neutrinos with a fourth neutrino mass state in the eV range.
Highlights
In this work, we update our previous analyses from refs. [11, 14, 21] to incorporate new experimental results
By combining the time evolution of the observed reactor anti-neutrino spectra with the known evolution of the reactor fuel composition, the Daya Bay collaboration was able to determine independently the neutrino fluxes from the two most important fissible isotopes in a nuclear reactor, 235U and 239Pu. Their analysis suggests that the discrepancy between predicted and observed fluxes stems mainly from 235U, while the neutrino flux from 239Pu appears consistent with predictions. (The other potentially relevant isotopes 238U and 241Pu are subdominant in Daya Bay.) In contrast, oscillations into sterile neutrinos would lead to equal flux deficits in all isotopes
In our previous paper [21] we have shown that both hypotheses give acceptable fits to Daya Bay data, and that the preference in favour of flux rescaling decreases once Daya Bay is combined with the global reactor data
Summary
The topic of this paper are scenarios in which the standard three-flavor framework for neutrino oscillations is augmented by adding one sterile neutrinos νs. For the following discussion the so-called short-baseline limit of eq (2.1) will be useful. This limit refers to the situation where ∆m221L/4E 1, ∆m231L/4E 1, so that standard three-flavor oscillations have not had time to develop yet. In this case, eq (2.1) generically simplifies to PαSαBL = 1 − 4|Uα4|2(1 − |Uα4|2) sin. In the νe and νe disappearance channels, the most important constraints on sterile neutrinos come from reactor experiments at short baseline (L 1 km).
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