View Single Post
Vanadium 50
#14
Mar3-08, 07:58 AM
Mentor
Vanadium 50's Avatar
P: 16,317
Quote Quote by arivero View Post
But suppose that the up quark were massless. Could the neutral pion decay into a pair of up, anti-up quarks?
The pion is already composed of u-ubar quarks, so I don't know what a decay to u-ubar would mean. Since quarks are confined, you'll end up with a pi0 anyway, so that's not much of a decay.

There is an additional subtlety - a pi0 composed of massless quarks would itself be massless (it becomes a Goldstone) and massless particles do not decay.