Enhancing Sensitivity to Leptonic CP Violation using Complementarity among DUNE, T2HK, and T2HKK

TL;DR

This paper investigates how combining data from DUNE, T2HK, and T2HKK experiments can significantly improve the sensitivity to leptonic CP violation, overcoming individual limitations and degeneracies in neutrino oscillation measurements.

Contribution

It demonstrates that the combined analysis of these experiments enhances CP violation detection coverage, even with reduced exposures and systematic uncertainties, and explores optimal configurations.

Findings

Combination of experiments achieves >75% CP coverage for all $ heta_{23}$ values.

Half-exposure combined setup can reach >80% CP coverage with T2HKK and DUNE.

Systematic uncertainty reduction improves CP violation sensitivity notably.

Abstract

After the landmark discovery of non-zero $\theta_{13}$ by the modern reactor experiments, unprecedented precision on neutrino mass-mixing parameters has been achieved over the past decade. This has set the stage for the discovery of leptonic CP violation (LCPV) at high confidence level in the next-generation long-baseline neutrino oscillation experiments. In this work, we explore in detail the possible complementarity among the on-axis DUNE and off-axis T2HK experiments to enhance the sensitivity to LCPV suppressing the $\theta_{23}-\delta_{\mathrm{CP}}$ degeneracy. We find that none of these experiments individually can achieve the milestone of 3$\sigma$ LCPV for at least 75% choices of $\delta_{\mathrm{CP}}$ in its entire range of $[-180^{\circ} , 180^{\circ}]$, with their nominal exposures and systematic uncertainties. However, their combination can attain the same for all values of $\theta_{23}$ with only half of their nominal exposures. We observe that the proposed T2HKK setup in combination with DUNE can further increase the CP coverage to more than 80% with only half of their nominal exposures. We study in detail how the coverage in $\delta_{\mathrm{CP}}$ for $\ge$ 3$\sigma$ LCPV depends on the choice of $\theta_{23}$, exposure, optimal runtime in neutrino and antineutrino modes, and systematic uncertainties in these experiments in isolation and combination. We find that with an improved systematic uncertainty of 2.7% in appearance mode, the standalone T2HK setup can provide a CP coverage of around 75% for all values of $\theta_{23}$. We also discuss the pivotal role of intrinsic, extrinsic, and total CP asymmetries in the appearance channel and extrinsic CP asymmetries in the disappearance channel while analyzing our results.