To produce a narrow band beam, one starts from an almost monochromatic + beam

To produce a narrow band ν_μ beam, one starts from an almost monochromatic π⁺ beam (neglecting K⁺ contamination) and lets the pions decay as π⁺ → μ⁺+ν_μ. Assume the pion energy to be E_π = 200 GeV. Find the neutrino energy in the π⁺ rest frame. In the laboratory frame, the neutrino energy depends on the decay angle θ. Find the maximum and minimum neutrino energy. Find the laboratory angle θ of neutrinos emitted in the CM frame at θ* = 50 mrad.