Enhancing the hierarchy and octant sensitivity of ESS$ν$SB in conjunction with T2K, NO$ν$A and ICAL@INO

Abstract

The main aim of the ESS$ν$SB proposal is the discovery of the leptonic CP phase $δ_{CP}$ with a high significance ($5σ$ for 50% values of $δ_{CP}$) by utilizing the physics at the second oscillation maxima of the $P_{μe}$ channel. It can achieve $3σ$ sensitivity to hierarchy for all values of $δ_{CP}$. In this work, we concentrate on the hierarchy and octant sensitivity of the ESS$ν$SB experiment. We show that combining the ESS$ν$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$ν$A assuming their full runtime and present the combined sensitivity of ESS$ν$SB + ICAL@INO + T2K + NO$ν$A. We show that while by itself ESS$ν$SB can have up to $3σ$ hierarchy sensitivity, the combination of all the experiments can give up to $5σ$ sensitivity depending on the true hierarchy-octant combination. The octant sensitivity of ESS$ν$SB is low by itself. However the combined sensitivity of all the above experiments can give up to $3σ$ 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.