Revising the Solution of the Neutrino Oscillation Parameter Degeneracies at Neutrino Factories

Abstract

In the context of neutrino factories, we review the solution of the degeneracies in the neutrino oscillation parameters. In particular, we have set limits to $\sin^2 2θ_{13}$ in order to accomplish the unambiguous determination of $θ_{23}$ and $δ$. We have performed two different analysis. In the first, at a baseline of 3000 km, we simulate a measurement of the channels $ν_e\toν_μ$, $ν_e\toν_τ$ and $\barν_μ\to\barν_μ$, combined with their respective conjugate ones, with a muon energy of 50 GeV and a running time of five years. In the second, we merge the simulated data obtained at L=3000 km with the measurement of $ν_e\toν_μ$ channel at 7250 km, the so called 'magic baseline'. In both cases, we have studied the impact of varying the $ν_τ$ detector efficiency-mass product, $(ε_{ν_τ}\times M_τ)$, at 3000 km, keeping unchanged the $ν_μ$ detector mass and its efficiency. At L=3000 km, we found the existance of degenerate zones, that corresponds to values of $θ_{13}$, which are equal or almost equal to the true ones. These zones are extremely difficult to discard, even when we increase the number of events. However, in the second scenario, this difficulty is overcomed, demostrating the relevance of the 'magic baseline'. From this scenario, the best limits of $\sin^2 2θ_{13}$, reached at $3σ$, for $\sin^2 2θ_{23}=0.95$, 0.975 and 0.99 are: 0.008, 0.015 and 0.045, respectively, obtained at $δ=0$, and considering $(ε_{ν_τ}\times M_τ) \approx 125$, which is five times the initial efficiency-mass combination.