content_image/320526.jpg content_image/320522.jpg content_image/320523.jpg content_image/320524.jpg content_image/320525.jpg content_image/320527.jpg content_image/320530.jpg content_image/320533.jpg content_image/320531.jpg content_image/320532.jpg
M$_{Q}$ and the photon has mass m$_{γ}$ . The relevant four-vectors are now 

The full matrix element is then 

<img src='content_image/320526.jpg'>

<img src='content_image/320522.jpg'>

<img src='content_image/320523.jpg'>

<img src='content_image/320524.jpg'>

<img src='content_image/320525.jpg'>

<img src='content_image/320527.jpg'>

where Peskin’s trick, Eq. (E.11), was used. The latter amplitude corresponds to factorized production and will be dropped. We need the following relations 

<img src='content_image/320530.jpg'>

<img src='content_image/320533.jpg'>

<img src='content_image/320531.jpg'>

<img src='content_image/320532.jpg'>

