Gama gamma interaction

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

The Attempt at a Solution

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nrqed
Homework Helper
Gold Member
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

The Attempt at a Solution

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?

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

nrqed
Homework Helper
Gold Member
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
By definition in the center of mass frame the magnitudes of pA and pB are equal. That's the definition. we are talking about three-momentum, here, of course.