# Mass conservation in meson theory

In the Meson theory of nuclear forces, exchange of pi meson is given by:

$$n\rightarrow n + \pi^{0}$$
$$p\rightarrow p + \pi^{0}$$
$$n\rightarrow p + \pi^{-}$$
$$p\rightarrow n + \pi^{+}$$

Here the charge is conserved. But I don't understand how mass conservation takes place as in some of the cases a lighter mass gives rise to a heavier mass as in case of protons giving rise to neutons. So how is mass conservation obeyed here and mass of pion is estimated?

Mass conservation? Total energy must be conserved, but mass is not. The incident particle (or original particle) must have some energy available (say through kinetic energy) to emit the pion.
Make sense?
Cheers,
Ryan

Hi Ryan, thank you for replying. So the energy is conserved here. However, pions do have mass. How is this mass estimated?

Reshma said:
Hi Ryan, thank you for replying. So the energy is conserved here. However, pions do have mass. How is this mass estimated?