The muon decays as μ μ + → → e + + ν ν e + ν ν ¯ ¯ μ μ and μ μ − − → → e − − + ν ν ¯ ¯ e + ν ν μ μ . Decays without neutrino emission, such as μ μ + → → e + + γ γ , μ μ − − → → e − − + γ γ , μ μ + → → e + + e − − + e + and μ μ − − → → e − − + e + + e − − are so unlikely that they are considered prohibited and their observation would be considered evidence of new physics. A number of experiments are pursuing this path such as Mu to E Gamma, Comet, and Mu2e for μ μ + → → e + γ γ and Mu3e for μ μ + → → e + e − − e + .