I was recently reading "Particle Physics: A Very Short Introduction" by Oxford University Press, and in it (I haven't finished it yet though) he says,

"The weak force changes one variety of particle into another, such as in certain forms of of radioactivity. It can change a proton into a neutron, or vice versa, leading to transmutation of the elements. In doing so it also liberates particles known as neutrinos."

Being someone who thinks best with a diagram, I drew this based on the available information.

Neutrino interactions

To me, it appears that a neutrino must have an negative charge to cancel the charge or the proton and make it neutral. The knowledge that a neutron is ever so slightly heavier than proton just seems to confirm that the neutron is actually a tightly bound unit of a proton and a neutrino. However, I also know that neutrinos are said to have zero charge, and I know (or thought I did) the neutron is composed of 3 quarks.

Obviously the neutrino cannot have a charge, or the billions of neutrinos zipping around would interact with matter far more than they do. They certainly live up to their nickname of "ghost particles", so what's going on here?

My best guess is the book is an oversimplifying things, or saving them for a later chapter.


1 Answer 1


The quote is correct but a bit misleading. The statement "In doing so it also liberates particles known as neutrinos" includes electrons also which are the other particle that is released in neutron decay, and is the way that beta decays were discovered. The neutrino was discovered because neutron decay showed a three body momentum spectrum for the beta/electron meaning something was taking momentum away. This something was called neutrino.

This is what really happens, a down quark through the weak force transmutes to an up quark the W releasing an electron and the unseen neutrino.

neutron decay

The Feynman diagram for beta decay of a neutron into a proton, electron, and electron antineutrino via an intermediate heavy W boson

  • $\begingroup$ In answer to the OP's question: see from Anna's diagram that there is also an electron which balances the charge (neutrinos are indeed uncharged). $\endgroup$ Sep 25, 2015 at 4:53
  • $\begingroup$ Thank you for the clarification, that makes a lot more sense. Obviously I still have a lot to learn, and I look forward to doing so. :) $\endgroup$
    – CoilKid
    Sep 25, 2015 at 5:07

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