# Charged current vs. neutral current neutrino interactions

I am doing research related to the detection potential of neutrino detectors and, in looking up the various neutrino interaction channels that exist in each detector, I have found the interactions being classified as "charged-current" and "neutral-current" interactions. I have come across this terminology before and know it has to do with the nature of the interactions at the particle level. I also remember the adage "there are no flavor-changing neutral currents," if that applies here.

I've found that differentiating charged-current and neutral-current interactions is most relevant in the context of so-called "scintillator" detectors, which use hydrocarbons (with approximate chemical formula C$_n$H$_{2n}$) as the primary interaction medium. I would like some to explain to me, in the context of neutrino-matter interactions, what qualifies as a charged-current interaction and what qualifies as a neutral-current interaction. You can use the scintillator-relevant interactions in Table 1 of this paper for specific examples.

Feel free to use Feynman diagrams in your explanation if it helps, I am familiar with them.

At the tree level (i.e. the simplest Feynman diagram) the both types of weak interaction result from the exchange of a weak boson. The weak bosons are the $Z^0$ (neutral) and the $W^\pm$ (charged).

Guess how we assign the terms "neutral" and "charged" to weak interactions. Right, by the exchange boson. (We don't distinguish between interaction involving the two $W$ bosons for technical reasons.)

In hadronic neutrino interaction (ones involving a nucleon) you can tell the two classes apart by noting if the neutrino continues on it's way (neutral) or if a charged lepton ($e$, $\mu$ or $\tau$) appears in it's place (charged).

This doesn't work for leptonic interaction where the neutrino has the same flavor as the other lepton because of the possible presence of the exchange diagram.

(Image from http://inspirehep.net/record/1236362/files/TwoDiagrams.png) Notice that both diagrams have the same input state and the same output state.

• So, you're saying neutral current interactions exchange a $Z$ boson and charged current interactions exchange a $W$ boson? If so, in the diagram you included in your answer, you're saying $\nu_e + e^- \rightarrow \nu_e + e^-$ can be either neutral current or charged current? – NeutronStar Jan 2 '15 at 18:59
• That's right. There is still more ambiguity if you allow loop diagrams, but at low energy the weak coupling constant is small enough that the issue is ignorable. – dmckee Jan 2 '15 at 19:30
• I do not have experience with Feynman diagrams but I would like to ask if there is any reason why, in the right-side diagram, both electrons are in the bottom and, in the left-side diagram, they are not. – Stefano Jan 28 '18 at 19:56
• @Stefano In the $Z^0$ scattering diagram the interaction is purely impulsive (there is an exchange of energy and momentum between the particles and nothing else). In the other diagram the carrier boson is charged and causes the particles to change their identity. – dmckee Jan 28 '18 at 22:54