Probabilities and Alpha EM

[Royston]

How are the probabilites derived for the outcome of electron and positron high energy collisions using the Alpha Em constant, is the same method used with Alpha S e.g to find the probability of the emission of a gluon ?

[Severian]

For the first part of the question you will have to go read a textbook or attend a course, because it is far too complicated.

 

For the second but, yes, it is calculated in pretty much the same way. There are some subtleties though: for example, the quarks and gluons are representations of SU(3) rather than U(1) so the maths is a wee bit more complex. Also you have to be careful to ensure you are at a high enough energy - since alpha_s changes with energy, it is too large to use perturbation theory below about 1 GeV.

[Royston]

For the first part of the question you will have to go read a textbook or attend a course, because it is far too complicated.

 

Ok, thanks Severian, my current course pretty much said the same thing. I just wasn't content with not knowing the method, I'm sure it's covered in later courses...a couple of years from now, so I'll just have to wait.

[Severian]

If you think you can handle the maths, this course gets as far as cross-sections without using Quantum Field Theory. (It is a bit hand wavey but it gives you the idea.)

[Royston]

Thanks Severian, the maths is a bit beyond my scope for now, but I've saved the course on my hard drive for future reference.