(adsbygoogle = window.adsbygoogle || []).push({}); (urgent) Can someone help me understand the factors in the Breit-Wigner formula?

Hi, I have the BW formula as:

[tex]

\sigma = \frac{\lambda^2 (2J+1)}{\pi (2S_a+1)(2S_b+1)} \frac{\Gamma^2 / 4}{(E-E_R)^2 + \Gamma^2/4}

[/tex]

So [tex]E_R[/tex]: this is described as the 'resonance energy'. I'm pretty sure this is the energy of the resonant state (i.e. of the compound particle) - is this the compound particle's mass as well? Or does the compound particle have kinetic energy?

Then E: This is described as 'the centre of mass energy of the initial state'. Does this include both rest energy and kinetic energy? And say we had a nucleus incident on a stationary nucleus, how would we calculate E?

The other symbols are fine.

Thanks very much.

EDIT:

Oh something else confuses me. Often you get plots of cross section vs. energy (e.g. incident neutron energy), and there are multiple peaks. Is [tex]E_R[/tex] different for all these peaks?

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# Can someone help me understand the factors in the Breit-Wigner formula?

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