Determining the Neutrino Mass Hierarchy with INO, T2K, NOvA and Reactor Experiments

TL;DR

This paper evaluates the potential of combined data from INO, T2K, NOvA, and reactor experiments to determine the neutrino mass hierarchy, emphasizing the advantages of atmospheric neutrino observations with earth matter effects.

Contribution

It provides a detailed sensitivity analysis of the INO-ICAL detector's ability to determine the neutrino mass hierarchy when combined with other experiments, considering realistic detector simulations.

Findings

Combined data could achieve up to 5.7σ significance in hierarchy determination.

Atmospheric neutrino data from INO enhances hierarchy sensitivity independent of δ_CP.

The study demonstrates the importance of multi-experiment synergy for neutrino physics.

Abstract

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 $2.3\sigma-5.7\sigma$ discovery of the neutrino mass hierarchy, depending on the true value of $\sin^2\theta_{23}$ [0.4 -- 0.6], $\sin^22\theta_{13}$ [0.08 -- 0.12] and $\delta_{CP}$ [0 -- 2$\pi$].