Griffiths Introduction to Elementary Particles · Problem 3.13

Symmetries — David J. Griffiths

Physics — QFT · relativistic-kinematics-decay

Problem

A pion traveling at speed

v

decays into a muon and a neutrino,

\pi \to \mu + \nu

. If the neutrino emerges at 90° to the original pion direction, at what angle does the

\mu

come off? [

Answer

\tan\theta = (1 - m_\mu^2/m_\pi^2)/(2\beta\gamma^2)

]