Solar Parameters in Long-Baseline Accelerator Neutrino Oscillations

Long-baseline (LBL) accelerator neutrino oscillation experiments, such as NOvA and T2K in the current generation, and DUNE-LBL and HK-LBL in the coming years, will measure the remaining unknown oscillation parameters with excellent precision. These analyses assume external input on the so-called “solar parameters,” θ$_{12}$ and $ \Delta {m}_{21}^2 $, from solar experiments such as SNO, SK, and Borexino, as well as reactor experiments like KamLAND. Here we investigate their role in long-baseline experiments. We show that, without external input on $ \Delta {m}_{21}^2 $ and θ$_{12}$, the sensitivity to detecting and quantifying CP violation is significantly, but not entirely, reduced. Thus long-baseline accelerator experiments can actually determine $ \Delta {m}_{21}^2 $ and θ$_{12}$, and thus all six oscillation parameters, without input from any other oscillation experiment. In particular, $ \Delta {m}_{21}^2 $ can be determined; thus DUNE-LBL and HK-LBL can measure both the solar and atmospheric mass splittings in their long-baseline analyses alone. While their sensitivities are not competitive with existing constraints, they are very orthogonal probes of solar parameters and provide a key consistency check of a less probed sector of the three-flavor oscillation picture. Furthermore, we also show that the true values of $ \Delta {m}_{21}^2 $ and θ$_{12}$ play an important role in the sensitivity of other oscillation parameters such as the CP violating phase δ.