Pion decay

[Warren Wolfe]

Can anyone tell me the specific quark interactions that take place in pion
decay? The end products are all leptons (a muon and a neutrino) so what
becomes of the up and anti-down quarks? My guess is something like u -> d +
W(+) and the d annihilates with the anti-d. The W(+) can decay to a muon
plus a neutrino, but what are the by products of the annihilation process?
Or is what happens completely different?

Thanks for any help,
Warren Wolfe

[Jon Bell]

In article <81Isd.149097$5K2.118671@attbi_s03>,

Warren Wolfe <wwol...@comcast.net> wrote:
>Can anyone tell me the specific quark interactions that take place in pion
>decay? The end products are all leptons (a muon and a neutrino) so what
>becomes of the up and anti-down quarks? My guess is something like u -> d +
>W(+) and the d annihilates with the anti-d. The W(+) can decay to a muon
>plus a neutrino, but what are the by products of the annihilation process?

I think that one way to think of it is that the incoming d is more or less
equivalent to an outgoing anti-d.

Another way to think of it might be that u + anti-d -> W is a weak-force
annihilation process, analogous to the usual electromagnetic annihilation
process, in which a photon comes out. In both cases, two fermions come in
and a vector (gauge) boson comes out.

--
Jon Bell <jtbe...@presby.edu> Presbyterian College
Dept. of Physics and Computer Science Clinton, South Carolina USA

[EjP]

Warren Wolfe wrote:

> Can anyone tell me the specific quark interactions that take place in pion
> decay? The end products are all leptons (a muon and a neutrino) so what
> becomes of the up and anti-down quarks? My guess is something like u -> d +
> W(+) and the d annihilates with the anti-d.

You don't need the extra step. The incoming dbar is equavalent to an
outgoing d. u+ dbar -> W+ -> mu+ + nu_mu as described here:
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/piondec.html

> The W(+) can decay to a muon
> plus a neutrino, but what are the by products of the annihilation process?

The muon and the neutrino *are* the byproducts of the decay process.

-E