content_image/323776.jpg content_image/323775.jpg content_image/323774.jpg content_image/323772.jpg content_image/323773.jpg
The differential elastic cross-section is given by 

<img src='content_image/323776.jpg'>

where v$_{1}$ and v$_{2}$ are the velocities of the φ and χ particles before the collision respectively, where v$_{2}$ = c . As we are setting c =1 , the first term in Eq. (B.5) ≈ 1 . Collecting terms together gives 

Integrating this gives 

<img src='content_image/323775.jpg'>

<img src='content_image/323774.jpg'>

From the 4-momenta of p$_{1}$ and p$_{3}$ , Eqs. (B.1) and (B.3) respectively, we have 

and 

<img src='content_image/323772.jpg'>

<img src='content_image/323773.jpg'>

