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Register a new userHierarchy sensitivity of NO$ u$A in light of T2K $ u_e$ appearance data
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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.
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The main aim of the ESS$ u$SB proposal is the discovery of the leptonic CP phase $delta_{CP}$ with a high significance ($5sigma$ for 50% values of $delta_{CP}$) by utilizing the physics at the second oscillation maxima of the $P_{mu e}$ channel. It can achieve $3sigma$ sensitivity to hierarchy for all values of $delta_{CP}$. In this work, we concentrate on the hierarchy and octant sensitivity of the ESS$ u$SB experiment. We show that combining the ESS$ u$SB experiment with the atmospheric neutrino data from the proposed India-based Neutrino Observatory(INO) experiment can result in an increased sensitivity to mass hierarchy. In addition, we also combine the results from the ongoing experiments T2K and NO$ u$A assuming their full runtime and present the combined sensitivity of ESS$ u$SB + ICAL@INO + T2K + NO$ u$A. We show that while by itself ESS$ u$SB can have up to $3sigma$ hierarchy sensitivity, the combination of all the experiments can give up to $5sigma$ sensitivity depending on the true hierarchy-octant combination. The octant sensitivity of ESS$ u$SB is low by itself. However the combined sensitivity of all the above experiments can give up to $3sigma$ sensitivity depending on the choice of true hierarchy and octant. We discuss the various degeneracies and the synergies that lead to the enhanced sensitivity when combining different experimental data.
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$A and T2K in the appearance channel.
The first hint of neutrino mass hierarchy is expected to come from the NO$ u$A experiment in Fermilab as the present best-fit parameter space i.e., normal hierarchy and $delta_{CP}=-90^circ$ is the favourable parameter space for NO$ u$A where there is no degeneracy. But this situation may change if the standard three flavour framework is not complete and there is existence of new physics. In this work we consider the presence of an extra light sterile neutrino at the eV scale and study the new degeneracies which are absent in the standard three flavour framework. We also study the effect of these new degeneracies on the hierarchy measurement of NO$ u$A.
Leptonic textit{CP} violation search, neutrino mass hierarchy determination, and the precision measurement of oscillation parameters for a unitary test of the leptonic mixing matrix are among the major targets of the ongoing and future neutrino oscillation experiments. The work explores the physics reach for these targets by around 2027, when the third generation of the neutrino experiments starts operation, with a combined sensitivity of three experiments: T2K-II, NO$ u$A extension, and JUNO. It is shown that a joint analysis of these three experiments can conclusively determine the neutrino mass hierarchy. Also, at certain values of emph{true} dcp, it provides closely around a $5sigma$ confidence level (C.L.) to exclude textit{CP}-conserving values and more than a $50%$ fractional region of emph{true} $delta_{text{CP}}$ values can be explored with a statistic significance of at least a $3sigma$ C.L. Besides, the joint analysis can provide unprecedented precision measurements of the atmospheric neutrino oscillation parameters and a great offer to solve the $theta_{23}$ octant degeneracy in the case of nonmaximal mixing.
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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