# Tag Info

Neutrino can interact only by exchange of electroweak boson. So in each reaction with neutrino $W^\pm$ or $Z$ bosons must be involved. Also, Standard Model neutrino is assumed to be massless, so there is defined handedness: neutrino is left-handed and antineutrino is right-handed. Consequence of it is that left-handed neutrino will interact only with ...
In the reaction that you ask about the exchange boson is space-like (meaning that for that particle $E^2 - (pc)^2$ takes on a negative value. In cases like that there is no unique way to decide if you have a $W^-$ going from the nucleon to the lepton or a $W^+$ going from the lepton to the nucleon, and the drawing is usually annotated only with a $W$. ...