# Feynman diagrams - neutrino interactions

1. Nov 28, 2009

### billbray

I have some well ordered feyman diagrams which have an incoming neutrino interacting at a vertex with a w boson and emitting an electron. since a neutrino can pass through some 18 light years of led without interacting, i'm wandering how a single neutrino interacts at this vertex?

2. Nov 29, 2009

Staff Emeritus
The interaction rate is small, but not zero. That's why it's 18 light years and not 180 or 1800.

3. Nov 29, 2009

### ansgar

The first thing you should think of is beta-decay where a neutrino is emitted, if a particle can be the final product, it can also be the initial probe (time symmetry).

here is the beta decay:
http://teachers.web.cern.ch/teachers/archiv/HST2002/feynman/exampl2.gif
(the wavy line is the W boson)

and this is the process if p was heavier than n:
http://hyperphysics.phy-astr.gsu.edu/Hbase/astro/imgast/ppfustep.gif

W couples to lepton and its neutrino, e.g. electron + (anti) electron neutrino (lepton # must be conserved)

Z couples to lepton and antilepton, e.g. eletron + positron / electron neutrino + anti electron neutrino

Neutrinos mainly interact with matter (as incoming particles) via inverse beta decay