What can we learn about the lepton CP phase in the next 10 years?

TL;DR

This paper evaluates how current accelerator and reactor experiments can constrain the lepton CP phase _{CP} over the next decade using a new sensitivity measure, highlighting the potential for significant exclusion of _{CP} space and hierarchy determination.

Contribution

It introduces the CP exclusion fraction as a new measure for global sensitivity to _{CP} and assesses the combined potential of T2K and NOvA experiments for CP phase constraints.

Findings

T2K and NOvA can exclude 50-60% and 40-50% of _{CP} space respectively at 90% CL in 10 years.

The synergy between T2K and NOvA can determine the mass hierarchy through CP sensitivity.

Significant _{CP} constraints are possible with dedicated antineutrino runs.

Abstract

We discuss how the lepton CP phase can be constrained by accelerator and reactor measurements in an era without dedicated experiments for CP violation search. To characterize globally the sensitivity to the CP phase \delta_{CP}, we introduce a new measure, the CP exclusion fraction, which quantifies what fraction of the \delta_{CP} space can be excluded at a given input values of \theta_{23} and \delta_{CP}. Using the measure we study the CP sensitivity which may be possessed by the accelerator experiments T2K and NOvA. We show that, if the mass hierarchy is known, T2K and NOvA alone may exclude, respectively, about 50%-60% and 40%-50% of the \delta_{CP} space at 90% CL by 10 years running, provided that a considerable fraction of beam time is devoted to the antineutrino run. The synergy between T2K and NOvA is remarkable, leading to the determination of the mass hierarchy through CP sensitivity at the same CL.