Abstract
We prove that, in any flavor transition, neutrino oscillation CP-violating asymmetries in matter have two disentangled components: (i)a CPT-odd T-invariant term, non-vanishing iff there are interactions with matter, and (ii)a T-odd CPT-invariant term, non-vanishing iff there is genuine CP violation. As function of the baseline, these two terms are distinct L-even and L-odd observables to separately test (i)matter effects sensitive to the neutrino hierarchy and (ii)genuine CP violation in the neutrino sector. For the golden ν_{μ}→ν_{e} channel, the different energy distributions of the two components provide a signature of their separation. At long baselines, they show oscillations in the low and medium energy regions, with zeros at different positions and peculiar behavior around the zeros. We discover a magic energy E=(0.91±0.01) GeV at L=1300 km with vanishing CPT-odd component and maximal genuine CP asymmetry proportional to sinδ, with δ the weak CP phase. For energies above 1.5GeV, the sign of the CP asymmetry discriminates the neutrino hierarchy.
Highlights
The last two decades have seen a revolution in neutrino physics with the discovery of, and precision studies on, flavor oscillations in atmospheric [1], solar [2], reactor [3], and accelerator [4] neutrinos
The concept exploited here is based on the fact that genuine and matter-induced CP violation have opposite behaviors [20] under the other discrete symmetries of time reversal T and CPT: whereas genuine CP violation is odd under T and even under CPT, the matter effect is T even and CPT odd
They are well separated in the effective Hamiltonian, in general, they are not in the experimental observables and, in particular, in the CP asymmetry
Summary
Matter-induced terms are welcome in order to obtain information on the neutrino mass hierarchy Because of this combined effect, the generalized attitude in the scientific community has been to extract the CP phase δ in the UPMNS mixing matrix from the global fits: a resulting value different from 0 or π is taken as evidence of CP violation. Such a methodology is, not guaranteeing that the experiment did observe CP violation—any quantity sensitive to δ would make this job, as happens in bare transition probabilities due to the CP conserving cos δ terms
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