Chapter 44, Problem 6P

(a) A stationary particle 1 decays into parties 2 and 3, which move off with equal but oppositely directed momenta. Show that the kinetic energy K₂ of particle 2 is given by

$K_2=\frac{1}{2E_1}\left[{\left(E_1-E_2\right)}^2-E_3^2\right]$,

where E₁, E₂, and E₃ are the rest energies of the particles.

(b) A stationary positive pion π⁺ (rest energy 139.6 MeV) can decay to an antimuon μ⁺ (rest energy 105.7 MeV) and a neutrino v (rest energy approximately 0). What is the resulting kinetic energy of the antimuon?