The mixing of three active neutrino flavors is parameterized by the unitary PMNS matrix. If there are more than three neutrino flavors and if the extra generations are heavy iso-singlets, the effective $$3\times 3$$ 3 × 3 mixing matrix for the three active neutrinos will be non-unitary. We have analyzed the latest T2K and NO$$\nu $$ ν A data with the hypothesis of non-unitary mixing of the active neutrinos. We found that the 2019 NO$$\nu $$ ν A data slightly (at $$\sim 1\, \sigma $$ ∼ 1 σ CL) prefer the non-unitary mixing over unitary mixing. In fact, allowing the non-unitary mixing brings the NO$$\nu $$ ν A best-fit point in the $$\sin ^2{\theta _{23}}-\delta _{\mathrm {CP}}$$ sin 2 θ 23 - δ CP plane closer to the T2K best-fit point. The 2019 T2K data, on the other hand, cannot rule out any of the two mixing schemes. A combined analysis of the NO$$\nu $$ ν A and T2K 2019 data prefers the non-unitary mixing at $$1\, \sigma $$ 1 σ CL. We derive constraints on the non-unitary mixing parameters using the best-fit to the combined NO$$\nu $$ ν A and T2K data. These constraints are weaker than previously found. The latest 2020 data from both the experiments prefer non-unitarity over unitary mixing at $$1\, \sigma $$ 1 σ CL. The combined analysis prefers non-unitarity at $$2\, \sigma $$ 2 σ CL. The stronger tension, which exists between the latest 2020 data of the two experiments, also gets reduced with non-unitary analysis.
T2K and NOνA collaborations have taken significant amount of data in both neutrino and antineutrino modes. For these two experiments, the best-fit values of ∆ 31 coincide and both prefer normal hierarchy over inverted hierarchy. However, NOνA allows inverted hierarchy at 1 σ whereas T2K barely allows it at 2 σ. Regarding δ CP , T2K rules out the upper half plane at 2 σ for NH and 3 σ for IH, whereas the best-fit value of NOνA is in the upper half plane. The two experiments also disagree on the best-fit value of sin 2 θ 23 . T2K prefers sin 2 θ 23 just above the maximal value of 0.5 while NOνA prefers a significantly higher value. These disagreements are the result of the tension between the data of the two experiments. In addition, there is tension between the neutrino and anti-neutrino disappearance data of NOνA and also between the neutrino appearance and disappearance data of T2K. In this report, we explain how these tensions lead to the strong discrepancy in the δ CP best-fit values. We also do a simple combined fit of the disappearance and the appearance data from these two experiments to explore possible trends in the determination of neutrino parameters.
The combined analysis of ν µ disappearance and ν e appearance data of NOνA experiment leads to three nearly degenerate solutions. This degeneracy can be understood in terms of deviations in ν e appearance signal, caused by unknown effects, with respect to the signal expected for a reference set of oscillations parameters. We define the reference set to be vacuum oscillations in the limit of maximal θ 23 and no CP-violation. We then calculate the deviations induced in the ν e appearance signal event rate by three unknown effects: (a) matter effects, due to normal or inverted hierarchy (b) octant effects, due to θ 23 being in higher or lower octant and (c) CP-violation, whether δ CP ∼ −π/2 or δ CP ∼ π/2. We find that the deviation caused by each of these effects is the same for NOνA. The observed number of ν e events in NOνA is equivalent to the increase caused by one of the effects. Therefore, the observed number of ν e appearance events of NOνA is the net result of the increase caused by two of the unknown effects and the decrease caused by the third. Thus we get the three degenerate solutions. We also find that further data by NOνA can not distinguish between these degenerate solutions but addition of one year of neutrino run of DUNE can make a distinction between all three solutions. The distinction between the two NH solutions and the IH solution becomes possible because of the larger matter effect in DUNE. The distinction between the two NH solutions with different octants is a result of the synergy between the anti-neutrino data of NOνA and the neutrino data of DUNE.
In this paper, we have analysed the latest data from NO$$\nu $$ ν A and T2K with the Lorentz invariance violation along with the standard oscillation hypothesis. We have found that the NO$$\nu $$ ν A data cannot distinguish between the two hypotheses at $$1\, \sigma $$ 1 σ confidence level. T2K data and the combined data analysis excludes standard oscillation at $$1\, \sigma $$ 1 σ . All three cases do not have any hierarchy sensitivity when analysed with LIV. There is a mild tension between the two experiments, when analysed with LIV, as $${\theta _{23}}$$ θ 23 at NO$$\nu $$ ν A best-fit is at higher octant but the same for T2K is at lower octant. The present data from accelerator neutrino long baseline experiments lose octant determination sensitivity when analysed with LIV. The tension between the two experiments is also reduced when the data are analysed with LIV.
Abstract:The moderately large value of θ 13 , measured recently by reactor experiments, is very welcome news for the future neutrino experiments. In particular, the NOνA experiment, with 3 years each of ν andν runs, will be able to determine the mass hierarchy if one of the following two favourable combinations is true: normal hierarchy with −180 • ≤ δ CP ≤ 0 or inverted hierarchy with 0 ≤ δ CP ≤ 180 • . In this report, we study the hierarchy reach of the first 3 years of NOνA data. Since sin 2 2θ 23 is measured to be non-maximal, θ 23 can be either in the lower or higher octant. Pure ν data is affected by θ 13 -hierarchy and octanthierarchy degeneracies, which limit the hierarchy sensitivity of such data. A combination of ν andν data is not subject to these degeneracies and hence has much better hierarchy discrimination capability. We find that, with a 3 year ν run, hierarchy determination is possible for only two of the four octant-hierarchy combinations. Equal 1.5 year runs in ν andν modes give good hierarchy sensitivity for all the four combinations.
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