
#1
Apr1408, 07:56 PM

P: 27

Hi guys,
Could someone show me how can I evaluate/measure the cross section of gamma+gamma > electron + positron I'll be thankful for your help 1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution 



#2
Apr1508, 11:15 AM

Sci Advisor
HW Helper
P: 2,886

have you done calculations of cross sections before? Have you done, say, Moller scattering? This is a long calculation so it's impossible to show you all the steps if you haven't done any calculations. If you have, I can help you get through steps if you are stuck. First, did you draw the Feynman diagrams? 



#3
Apr1508, 06:51 PM

P: 27

Thanks nrged
I have done the most of calculation. Where I got four terms of Trace {Amplitude}. As you knew in the C.M. we have a specific formula for differential cross section Diff. Cross Sect. = {1/{64* Pi^2)*(E1+E2)^2}*{p3/p1}*M^2 That is for interaction(in general) A+B> C+D My question is about p1 ? Is p1=pA or p1=pB ??? or do you think A and B have the same momentum in C.M. frame"even if they have different masses"? Thanks for you help 



#4
Apr1508, 07:34 PM

Sci Advisor
HW Helper
P: 2,886

gama gamma interaction 


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