Abstract
The latest data of the two long-baseline accelerator experiments NOνA and T2K, interpreted in the standard three-flavor scenario, display a discrepancy. A mismatch in the determination of the standard CP phase δ_{CP} extracted by the two experiments is evident in the normal neutrino mass ordering. While NOνA prefers values close to δ_{CP}∼0.8π, T2K identifies values of δ_{CP}∼1.4π. Such two estimates are in disagreement at more than 90%C.L. for 2degrees of freedom. We show that such a tension can be resolved if one hypothesizes the existence of complex neutral-current nonstandard interactions (NSIs) of the flavor changing type involving the e-μ or the e-τ sectors with couplings |ϵ_{eμ}|∼|ϵ_{eτ}|∼0.2. Remarkably, in the presence of such NSIs, both experiments point towards the same common value of the standard CP phase δ_{CP}∼3π/2. Our analysis also highlights an intriguing preference for maximal CP violation in the nonstandard sector with the NSI CP phases having best fit close to ϕ_{eμ}∼ϕ_{eτ}∼3π/2, hence pointing towards imaginary NSI couplings.
Highlights
Introduction.—The two long-baseline (LBL) accelerator experiments NOνA and T2K have recently released new data at the Neutrino 2020 Conference [1,2]
While NOνA prefers values close to δCP ∼ 0.8π, T2K identifies values of δCP ∼ 1.4π. Such two estimates are in disagreement at more than 90% C.L. for 2 degrees of freedom. We show that such a tension can be resolved if one hypothesizes the existence of complex neutral-current nonstandard interactions (NSIs) of the flavor changing type involving the e − μ or the e − τ sectors with couplings jεeμj ∼ jεeτj ∼ 0.2
In the presence of such NSIs, both experiments point towards the same common value of the standard CP phase δCP ∼ 3π=2
Summary
Nf being the number density of the f fermion. For the Earth, we can consider neutral and isoscalar matter, with Nn ≃ Np 1⁄4 Ne, in which case Nu ≃ Nd ≃ 3Ne. The NSIs alter the effective Hamiltonian of neutrino propagation in matter, which in the flavor basis reads
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