| MadSci Network: Physics |
To whom it concerns, Everything that you wrote is essentially correct. The charged pion does indeed decay through the weak interaction with a relatively long mean lifetime of 2.6E-8 seconds compared to the neutral pion which decays electromagnatically with the much shorter lifetime of only 8.4E-17 seconds. This is like comparing 10 years to 1 second! I discussed this difference in a previous post. http://www.madsci.org/posts/archives/2001-05/989934620.Ph.r.html Most of the time (99.98770%) the decay products are a muon and a muon antineutrino (for the negative pion) or an antimuon and a muon neutrino (for the positive pion). The virtual particle which mediates the decay to first order in perturbation theory is the W boson, the carrier of the weak force. The pion is a spin-zero particle while the W boson is a spin-one particle. All true. The confusion seems to be the way in which angular momentum is conserved from the initial zero angular momentum pion state to the intermediate virtual spin-one W boson state. A massive spin-one particle like the W boson has three possible spin states which you can think of as "up", "zero", and "down". The rules of quantum mechanics restrict the angular momentum to values from maximum (+1) to minimum (-1) separated by one unit, and zero is one of the allowed values. A W boson in the "zero" spin state will behave like a spinless particle. In the jargon, these are called longitudinally polarized W bosons. The pion lifetimes and branching ratios came from The Particle Data Group http://pdg.lbl.gov/2006/tables/mxxx.pdf --Dr. Randall J. Scalise http://www.phys.psu.edu/~scalise/
Try the links in the MadSci Library for more information on Physics.