# In neutrino oscillation experiment, such as NOvA, what particle does the neutrino interact with in the detector?

In such kind of schematic of Feynman diagrams involved in neutrino scattering with matter at neutrino oscillation experiments : (page labelled 54 = page 100 of the pdf file : http://inspirehep.net/record/1725915/files/fermilab-thesis-2018-30.pdf )

*What does the $$\nu_\mu$$ interact with : the neutron ? The muon ? Or the proton ?

*Same question for the diagram for $$\nu_e$$ : does it interact with the electron, the proton or the neutron ?

• I don't have time to write up how a neutrino physicist knows just by looking at the reactions, but there are lots of hints in the figure you posted. Notice the right-hand column of the figure. Those Feynman diagram give you explcit answer to the question in some cases (not withstanding that the author has draw them using the realtivist's choice of axes rather than the usual particle-physicists axes), and in the other lower panel the labling of the reconstructed event gives you the answer. – dmckee --- ex-moderator kitten Dec 17 '19 at 20:55
• @dmckee : yes, the main problem of my question is to know the direction of "time" in the Feynman diagrams. This corresponds mainly to my question. I do know the meaning of Feynman diagrams and had well seen that before to ask the question, which is still open. – Mathieu Krisztian Dec 17 '19 at 22:28
• Hello @dmckee, I found the solution : the time is going from bottom to the top. It is rather unconventional. Remark : there was no way from the diagram to deduce, because they could also have chosen to have the time from bottom right to top left, and so on. Would you know why they have chosen a convention different to modern particle physics, while NOvA neutrino experiment is a modern particle physics experiment... – Mathieu Krisztian Dec 17 '19 at 23:46
• I recognized the choice of axes immediately. This was possible because (a) I know that $\mathrm{NO}\nu\mathrm{A}$ uses a neutrino beam, so in diagrams the neutrino leg is an incident leg and (b) there are a very limited number of weak verticies. And anyone in the neutrino community as well as a large fraction of particle-physicists in other sub-disciplines would do the same. – dmckee --- ex-moderator kitten Dec 17 '19 at 23:51
• @dmckee sure, but it is not the question now : the question is "Would you know why they have chosen a convention different to modern particle physics, while NOvA neutrino experiment is a modern particle physics experiment... " – Mathieu Krisztian Dec 18 '19 at 1:04