please clarify

neelakash

In a standard model book I find this:
a particle of mass M can exist as a part of an intermediate state for time `h/(Mc^2) where `h=h/2π


I cannot understand the underlined part.Which intermediate state are they referring to?

LastGuyOnTheLeft

Spontaneously I would say that with "as a part of an intermediate state" the mean a state like, for example, the Z in the following diagram?
http://www-sldnt.slac.stanford.edu/a...s/epem_toZ.jpg

That is, it can not be the final product, but only exist for the time [tex]\hbar/(Mc^{2})[/tex] before it need to decay into something else.

neelakash

Since I do not know very much the Weak interaction...are you sure that it would be a Z boson in a Feynmann diagram?Do not take me otherwise,the formula holds for any type of bosons:like photon.Since photon mass is zero,the lifetime and range of photon is infinite...So,in such cases how will you explain the intermediate state?

neelakash

OK buddy you are correct.The point where I was stumbling is clear now.Thank you.

Barmecides

Experimentally, we often caracterize particles as resonances (when the particle is unstable).
In the case of the Z quoted above you can find the resonance plot on this web page (first plot) :
http://aleph.web.cern.ch/aleph/aleph...b/physics.html
Below the resonance, contributions of feynman graphs like e+e- -> photon* -> qq are negligible.