Homework Help: Qq- ->qq- differential cross section and mandelstam variables

1. Nov 17, 2012

helpcometk

qq- --->qq- differential cross section and mandelstam variables

1. The problem statement, all variables and given/known data
for the problem statement please look the attachement

2. Relevant equations
The problem is asking to express the mandelstam variables in temrs of the scattering angle θ.I would like to ask the quastion weather there varibles should depend on qq- --->qq- process or they are the same for any process A+B--->A+B ? And then what does it mean massless limit i.e WHICH masses become zero ?
It is not obvious from where i should start to calculate the mandslestam variables in terms of the scaterring angle.

3. The attempt at a solution

Attached Files:

• MV.PNG
File size:
10.9 KB
Views:
157
2. Nov 18, 2012

andrien

Re: qq- --->qq- differential cross section and mandelstam variables

I think you know about those s,t and u.you may also be aware of fact that only two of it are independent because of the relation
s+t+u=4m2
since everything is asked in cm frame,so it is easy.Because in rest frame as you can show
s=4E2=4(|p|2+m2)
t=-2|p|2(1-cosθ)
u=-2|p|2(1+cosθ),since |p|=|p'|
massless limit is also called high energy limit,in which E>>m,so you can neglect m in comparison to |p|.θ is scattering angle in CM system.

3. Nov 20, 2012

helpcometk

Re: qq- --->qq- differential cross section and mandelstam variables

thanks