In a Feynman diagram, the arrows on the charged particles are along the direction of negative charge flow. As a result, the arrow is not always directed from the vertex of creation and not always directed towards the vertex of annihilation. The antineutrino and neutron in $\beta$-decay carry no charge. What is the convention of arrow in the Feynman diagram of $\beta$-decay? Sometimes I see arrows on neutral particles and sometimes don't. When arrows are given, they point the direction towards the vertex where neutron is destroyed and towards the vertex where the antineutrino is created. What is the solution?


Depending on how the arrow is pointing with respect to the vertex, it denotes a particle or an antiparticle of the name displayed.

feynman diagram

For incoming the into the vertex arrow denotes an electron, so it is e_ e_ scattering.

The same diagram with the time reversed, would denote positron postron scattering.

In beta minus decay


the electron arrow is pointing away from the outgoing vertex, and the electron antineutrino towards the outgoing vertex.

(I replaced the diagram since this also shows the quark content and the incoming vertex correctly.)


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