Search

The latest data from the T2K and NO ν A experiments show a tension in their preferred values of the oscillation parameters. In this work, we try to identify the source of the tension between the data from these two experiments. An analysis of their data from various channels (individually, and combined) shows that the tension arises primarily from the ν e appearance data, and is compounded by the ν ¯ μ disappearance data. We provide an explanation for the tension based on parameter degeneracies. Apart from the analysis with the standard matter effect, we also analyse the data with the vacuum oscillation hypothesis. We find that vacuum oscillations fit the data as well as matter effects do; and also reduce the tension between the two experiments. We have also done a study of the future run of NO ν A, T2K and DUNE in the context of establishing this tension with higher statistical significance. [ABSTRACT FROM AUTHOR]

The ν μ → ν e oscillation probability over a short baseline (≲1 km) would be negligible for the case when the mixing matrix for three active neutrinos is unitary. However, in the case of a non-unitary mixing of three neutrinos, this probability would be non-negligible due to the so-called "zero distance" effect. Hence, the near detector of accelerator experiments such as NO ν A can provide strong constraints on the parameters of the non-unitary mixing with very large statistics. By analyzing the NO ν A near-detector data, we find that the non-unitary mixing does not improve fits to the ν e or ν μ events over the standard unitary mixing. This leads to constraints on the non-unitary parameters: α 00 > 0.911 , | α 10 | < 0.020 , and α 11 > 0.952 at 90% C.L. A combined analysis with the near- and far-detector data does not change these constraints significantly. [ABSTRACT FROM AUTHOR]

The neutrino oscillation probabilities at the long-baseline accelerator neutrino experiments are expected to be modified by matter effects. We search for evidence of such modification in the data of T2K and NO ν A, by fitting the data to the hypothesis of (a) matter modified oscillations and (b) vacuum oscillations. We find that vacuum oscillations provide as good a fit to the data as matter modified oscillations. Even extended runs of T2K and NO ν A, with five years in neutrino mode (5 ν) and five years in anti-neutrino mode (5 ν ̄) , cannot make a 3 σ distinction between vacuum and matter modified oscillations. The future experiment DUNE, with neutrino and anti-neutrino runs of five years each (5 ν + 5 ν ̄) , can rule out vacuum oscillations by itself at 5 σ if the hierarchy is normal. If the hierarchy is inverted, a 5 σ discrimination against vacuum oscillations requires the combination of (5 ν + 5 ν ̄) runs of T2K, NO ν A and DUNE. [ABSTRACT FROM AUTHOR]

In this paper, we have estimated the neutrino mass ordering and the CP violation sensitivity of the proposed Protvino to ORCA (P2O) experiment after 6 years of data-taking. Both unitary and non-unitary 3 × 3 neutrino mass mixing have been considered in the simulations. A forecast analysis deriving possible future constraints on non-unitary parameters at P2O have been performed. [ABSTRACT FROM AUTHOR]

In this article, we review the status of the tension between the long-baseline accelerator neutrino experiments T2K and NOνA. The tension arises mostly due to the mismatch in the apappearance data of the two experiments. We explain how this tension arises based on ν μ → ν e and ν ¯ μ → ν ¯ e oscillation probabilities. We define the reference point of vacuum oscillation, maximal θ 23 and δ CP and compute the ν e / ν ¯ e appearance events for each experiment. We then study the effects of deviating the unknown parameters from the reference point and the compatibility of any given set of values of unknown parameters with the data from T2K and NOνA. T2K observes a large excess in the ν e appearance event sample compared to the expected ν e events at the reference point, whereas NOνA observes a moderate excess. The large excess in T2K dictates that δ CP be anchored at −90° and that θ 23   >   π / 4 with a preference for normal hierarchy. The moderate excess at NOνA leads to two degenerate solutions: (a) NH, 0   <   δ CP   <   180 ° , and θ 23   >   π / 4 ; (b) IH, − 180 °   <   δ CP   <   0 , and θ 23   >   π / 4 . This is the main cause of tension between the two experiments. We review the status of three beyond standard model (BSM) physics scenarios, (a) non-unitary mixing, (b) Lorentz invariance violation, and (c) non-standard neutrino interactions, to resolve the tension. [ABSTRACT FROM AUTHOR]

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 × 3 mixing matrix for the three active neutrinos will be non-unitary. We have analyzed the latest T2K and NO ν A data with the hypothesis of non-unitary mixing of the active neutrinos. We found that the 2019 NO ν A data slightly (at ∼ 1 σ CL) prefer the non-unitary mixing over unitary mixing. In fact, allowing the non-unitary mixing brings the NO ν A best-fit point in the 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 ν A and T2K 2019 data prefers the non-unitary mixing at 1 σ CL. We derive constraints on the non-unitary mixing parameters using the best-fit to the combined NO 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 σ CL. The combined analysis prefers non-unitarity at 2 σ CL. The stronger tension, which exists between the latest 2020 data of the two experiments, also gets reduced with non-unitary analysis. [ABSTRACT FROM AUTHOR]

We study the charged lepton flavour violation in a popular neutrino mass model with A 4 discrete symmetry. This symmetry requires the presence of multiple Higgs doublets in the model and it also dictates the flavour violating Yukawa couplings of the additional neutral scalars of the model. Such couplings lead to the decays of the neutral mesons, the top quark and the τ lepton into charged leptons of different flavours at tree level. The A 4 symmetry of the model leads to certain characteristic signatures in these decays. We discuss these signatures and predict the rates for the most favourable charged lepton flavour violating modes. [ABSTRACT FROM AUTHOR]

The combined analysis of νμ disappearance and νe appearance data of NOνA experiment leads to three nearly degenerate solutions. This degeneracy can be understood in terms of deviations in νe 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 θ23 and no CP-violation. We then calculate the deviations induced in the νe appearance signal event rate by three unknown effects: (a) matter effects, due to normal or inverted hierarchy (b) octant effects, due to θ23 being in higher or lower octant and (c) CP-violation, whether δCP~-π/2 or δCP~π/2. We find that the deviation caused by each of these effects is the same for NOνA. The observed number of νe events in NOνA is equivalent to the increase caused by one of the effects. Therefore, the observed number of νe 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. [ABSTRACT FROM AUTHOR]

The long baseline neutrino experiments, T2K and NO ν A, have taken significant amount of data in each of the four channels: (a) ν μ disappearance, (b) ν ̄ μ disappearance, (c) ν e appearance, and (d) ν ̄ e appearance. There is a mild tension between the disappearance and the appearance data sets of T2K. A more serious tension exists between the ν e appearance data of T2K and the ν e / ν ̄ e appearance data of NO ν A. This tension is significant enough that T2K rules out the best-fit point of NO ν A at 95% confidence level, whereas, NO ν A rules out T2K best-fit point at 90% confidence level. We explain the reason why these tensions arise. We also do a combined fit of T2K and NO ν A data and comment on the results of this fit. [ABSTRACT FROM AUTHOR]