Probing the octant of $\hat{I}{¸}_{23}$ with very long baseline neutrino oscillation experiments: a global look

Abstract

We investigate the baseline range in which the $\hat{I}{¸}_{23}$ degeneracy in neutrino oscillation probabilities is absent for fixed values of $\hat{I}{¸}_{13}$ and CP violation phase $\hat{I}{´}_{\mathrm{CP}}$. We begin by studying sensitivities of neutrino oscillation probabilities to $\hat{I}{¸}_{13}$, $\hat{I}{¸}_{23}$ and $\hat{I}{´}_{\mathrm{CP}}$ for very-long-baseline neutrino oscillations. We show contour graphs of the muon-neutrino survival probability $P(\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_{\hat{I}}¼)$ and the appearance probability $P(\hat{I}{½}_e\to \hat{I}{½}_{\hat{I}}¼)$ on the $\cos 2\hat{I}{¸}_{23}-\sin 2\hat{I}{¸}_{13}$ plane for baseline lengths $L=1000,5000,10000$, and 12000 km. For each baseline length, it is found that $P(\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_{\hat{I}}¼)$ is more sensitive to $\sin 2\hat{I}{¸}_{13}$ at energies around its local maximum while it is more sensitive to $\cos 2\hat{I}{¸}_{23}$ at energies around its local minimum. On the other hand, the appearance probability $P(\hat{I}{½}_e\to \hat{I}{½}_{\hat{I}}¼)$ is sensitive to $\sin 2\hat{I}{¸}_{13}$ and $\cos 2\hat{I}{¸}_{23}$ only near its local maximum. We observe that the $\hat{I}{¸}_{23}$ degeneracy in $P(\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_{\hat{I}}¼)$ is absent at energies around the local maximum of this probability, provided $\hat{I}{¸}_{13}$ is sufficiently large. The $\hat{I}{¸}_{23}$ degeneracy is also absent in general near the local maximum of $P(\hat{I}{½}_e\to \hat{I}{½}_{\hat{I}}¼)$. Using analytic approximations for neutrino oscillation probabilities, we demonstrate that the above observations for $L=1000,5000,10000,\mathrm{and}12000$ km are in fact valid for all distances. The implications of these results on probing the octant of $\hat{I}{¸}_{23}$ are discussed in details.

23 pages, 10 figures, 1 Table, revtex4