In the T2K experiment a is produced at the J-PARC proton accelerator and detected in

In the T2K experiment a ν_μ is produced at the J-PARC proton accelerator and detected in the water Cherenkov detector, Super-Kamiokande. The direction of the incoming neutrino is known, but not its energy E_ν. Consider the ‘quasi-elastic’interaction ν_μ + n → μ° + p. The energy E_μ of the muon and its direction θ_μrelative to that of the incoming neutrino are measured. How much is E_ν if E_μ = 0.5 GeV and θ_μ = 30°?