What is a first order process in particle physics

[j-lee00]

I was given the following question

Which of the reactions on the right are allowed by first-order processes? For those which are not allowed, state one conservation law which is violated.

What is a first order process in particle physics? i.e what does first order refer to? What would be a second order process?

Thanks
Jason

 

[fzero]

Think perturbation theory. A first-order process would be linear in some coupling constant. Equivalently it would involve a single interaction vertex. An nth order process would involve n interaction vertices and would be proportional to n factors of (possibly different) coupling constants.

 

[j-lee00]

Think perturbation theory. A first-order process would be linear in some coupling constant. Equivalently it would involve a single interaction vertex. An nth order process would involve n interaction vertices and would be proportional to n factors of (possibly different) coupling constants.

Thanks for you response

I am new to the subject so excuse my ignorance.

So the violation of laws that they are referring to are conservation of lepton no, baryon no, Charge (which are first order?). Where as weak and strong are second order?

 

[fzero]

Thanks for you response

I am new to the subject so excuse my ignorance.

So the violation of laws that they are referring to are conservation of lepton no, baryon no, Charge (which are first order?). Where as weak and strong are second order?

You seem to be confusing conservation laws with interactions. An interaction will conserve some quantities and possibly violate conservation of other quantities. You might want to post some of the processes that the problem is talking about so that. Also post a process that you understand and explain it so that I can understand what techniques you're meant to be using. I mean are you given an interaction term in a Lagrangian or just some list of allowed processes that you're supposed to compare with the processes in the problem?

 

[j-lee00]

I have attached it as a jpeg, the reactions are below in the pic not on the right

 

[fzero]

Let's consider process ii, e^- + p \rightarrow \nu_e + n. You need to determine the quarks that make up the initial particles and final particles. Do you know what weak interactions of quarks are allowed?Also, I think they may mean something different than I do when they say "first-order." If you can't find anything in your notes, perhaps we can deduce what they mean along the way.

 

[j-lee00]

For example the first reaction wrote that due to non conservation of electron lepton number, this reaction cannot procceed?

Thank you, I have to go

 

[Norman]

Also, I think they may mean something different than I do when they say "first-order." If you can't find anything in your notes, perhaps we can deduce what they mean along the way.

I think they mean tree level interactions.