Tuesday, March 27, 2018

particle physics - Breit-Wigner vs propagator?


Consider the two Feynman diagrams below:


Feynman diagrams, concerning the passage of a z-boson and a resonance.


I know for the second that we should use the Breit-wigner curve, but what about the first? If we go about using the propagator: 1˜q2m2zc2, (+ - - -) signature

then we a singularity when ˜q2=m2zc2 which is subverted when the Breit-Wigner curve is used. Thus my question is as follows: When is it appropriate to use the propagator as given above and when to use the Breit-Wigner curve.




No comments:

Post a Comment

classical mechanics - Moment of a force about a given axis (Torque) - Scalar or vectorial?

I am studying Statics and saw that: The moment of a force about a given axis (or Torque) is defined by the equation: $M_X = (\vec r \times \...