# The antineutrino in Beta decay

1. Dec 29, 2008

### ajassat

I understand the physical changes in beta decay that eventually lead to the virtual particle, a W- boson being formed. However I do not understand the physical changes that take place, which eventually lead to an antineutrino being emitted. What changes take place in the W- boson, that make it decay into an antineutrino and electron?

I would also be glad if someone could explain why the physical changes take place?

2. Dec 29, 2008

Staff Emeritus
I'm not sure that I understand what you mean. Also, you do understand that "a virtual particle being formed" is sort of a contradiction. The particle is virtual, not real. It's not formed.

3. Dec 29, 2008

### ajassat

By this do you mean that the antineutrino isn't really there after beta decay?
If the production of an antineutrino is virtual, then would you be able to explain how?

Simply, I would like to understand why we have an antineutrino involved ,regardless of it being real or virtual.

Thanks for attempting the answer the question.

4. Dec 29, 2008

Staff Emeritus
There is an antineutrino around to conserve spin (and other quantum numbers, like lepton number). If I have the decay $$n \rightarrow p + e^- + \overline{\nu}$$, I have a spin-1/2 object on the left hand side and without the neutrino, I have either a spin-0 or spin-1 ensemble on the right. I also have L = 0 on the left and L = 1 on the right. Finally, the energy spectrum of the electron is characteristic of three-body decays, not two body decays. For all of these reasons, one expects an additional particle produced, the antineutrino.

Of course, today those (anti-)neutrinos have been measured.

5. Dec 29, 2008

### ajassat

This has made me understand why it is necessary to produce an anti-neutrino in beta decay. So what are the spin and lepton values for the neutrino which help to create a balances on both sides of the decay?

6. Dec 29, 2008

### malawi_glenn

The neutrino is a spin 1/2 particle and a neutrino has lepton number +1 and an antineutrino has -1.

7. Dec 29, 2008

### ajassat

Thanks for this. I now understand how the anti-neutrino helps to balance things out.