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Register a new userTensions between the appearance data of T2K and NOvA
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The long baseline neutrino experiments, T2K and NOvA, have taken significant amount of data in each of the four channels: (a) $ u_mu$ disappearance, (b) $bar u_mu$ disappearance (c) $ u_e$ appearance and (d) $bar u_e$ appearance. There is a mild tension between the disappearance and the appearance data sets of T2K. A more serious tension exists between the $ u_e$ appearance data of T2K and the $ u_e / bar u_e$ appearance data of NOvA. This tension is significant enough that T2K rules out the best-fit point of NOvA at $95%$ confidence level whereas NOvA 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 NOvA data and comment on the results of this fit.
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The relatively large measured value of $theta_{13}$ has opened up the possibility of determining the neutrino mass hierarchy through earth matter effects. Amongst the current accelerator-based experiments only NOvA has a long enough baseline to observe earth matter effects. However, NOvA is plagued with uncertainty on the knowledge of the true value of $delta_{CP}$, and this could drastically reduce its sensitivity to the neutrino mass hierarchy. The earth matter effect on atmospheric neutrinos on the other hand is almost independent of $delta_{CP}$. The 50 kton magnetized Iron CALorimeter at the India-based Neutrino Observatory (ICAL@INO) will be observing atmospheric neutrinos. The charge identification capability of this detector gives it an edge over others for mass hierarchy determination through observation of earth matter effects. We study in detail the neutrino mass hierarchy sensitivity of the data from this experiment simulated using the Nuance based generator developed for ICAL@INO and folded with the detector resolutions and efficiencies obtained by the INO collaboration from a full Geant4-based detector simulation. The data from ICAL@INO is then combined with simulated data from T2K, NOvA, Double Chooz, RENO and Daya Bay experiments and a combined sensitivity study to the mass hierarchy is performed. With 10 years of ICAL@INO data combined with T2K, NOvA and reactor data, one could get about $2.3sigma-5.7sigma$ discovery of the neutrino mass hierarchy, depending on the true value of $sin^2theta_{23}$ [0.4 -- 0.6], $sin^22theta_{13}$ [0.08 -- 0.12] and $delta_{CP}$ [0 -- 2$pi$].
We study the impact of one light sterile neutrino on the prospective data expected to come from the two presently running long-baseline experiments T2K and NOvA when they will accumulate their full planned exposure. Introducing for the first time, the bi-probability representation in the 4-flavor framework, commonly used in the 3-flavor scenario, we present a detailed discussion of the behavior of the numu to nue and numubar to nuebar transition probabilities in the 3+1 scheme. We also perform a detailed sensitivity study of these two experiments (both in the stand-alone and combined modes) to assess their discovery reach in the presence of a light sterile neutrino. For realistic benchmark values of the mass-mixing parameters (as inferred from the existing global short-baseline fits), we find that the performance of both these experiments in claiming the discovery of the CP-violation induced by the standard CP-phase delta13 equivalent to delta, and the neutrino mass hierarchy get substantially deteriorated. The exact loss of sensitivity depends on the value of the unknown CP-phase delta14. Finally, we estimate the discovery potential of total CP-violation (i.e., induced simultaneously by the two CP-phases delta13 and delta14), and the capability of the two experiments of reconstructing the true values of such CP-phases. The typical (1 sigma level) uncertainties on the reconstructed phases are approximately 40 degree for delta13 and 50 degree for delta14.
A precise measurement of the atmospheric mass-squared splitting |Delta m^2_{mumu}| is crucial to establish the three-flavor paradigm and to constrain the neutrino mass models. In addition, a precise value of |Delta m^2_{mumu}| will significantly enhance the hierarchy reach of future medium-baseline reactor experiments like JUNO and RENO-50. In this work, we explore the precision in |Delta m^2_{mumu}| that will be available after the full runs of T2K and NOvA. We find that the combined data will be able to improve the precision in |Delta m^2_{mumu}| to sub-percent level for maximal 2-3 mixing. Depending on the true value of sin^2theta_{23} in the currently-allowed 3 sigma range, the precision in |Delta m^2_{mumu}| will vary from 0.87% to 1.24%. We further demonstrate that this is a robust measurement as it remains almost unaffected by the present uncertainties in theta_{13}, delta_{CP}, the choice of mass hierarchy, and the systematic errors.
The $ u_e$ appearance data of T2K experiment has given a glimpse of the allowed parameters in the hierarchy-$delta_{CP}$ parameter space. In this paper, we explore how this data affects our expectations regarding the hierarchy sensitivity of the NO$ u$A experiment. For the favourable combinations of hierarchy and $delta_{CP}$, the hierarchy sensitivity of NO$ u$A is unaffected by the addition of T2K data. For the unfavourable combinations, NO$ u$A data gives degenerate solutions. Among these degenerate solutions, T2K data prefers IH and $delta_{CP}$ in the lower half plane over NH and $delta_{CP}$ in the upper half plane. Hence, addition of the T2K data to NO$ u$A creates a bias towards IH and $delta_{CP}$ in the lower half plane irrespective of what the true combination is.
We study in detail the impact of a light sterile neutrino in the interpretation of the latest data of the long baseline experiments NO$ u$A and T2K, assessing the robustness/fragility of the estimates of the standard 3-flavor parameters with respect to the perturbations induced in the 3+1 scheme. We find that all the basic features of the 3-flavor analysis, including the weak indication ($sim$1.4$sigma$) in favor of the inverted neutrino mass ordering, the preference for values of the CP-phase $delta_{13} sim 1.2pi$, and the substantial degeneracy of the two octants of $theta_{23}$, all remain basically unaltered in the 4-flavor scheme. Our analysis also demonstrates that it is possible to attain some constraints on the new CP-phase $delta_{14}$. Finally, we point out that, differently from non-standard neutrino interactions, light sterile neutrinos are not capable to alleviate the tension recently emerged between NO$ u$A and T2K in the appearance channel.
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