# Parity violation in weak decays

1. Mar 7, 2013

### JoePhysicsNut

1. The problem statement, all variables and given/known data
I am confused about parity violation in weak decays. I learned about Wu's famous experiment and how it demonstrates that parity is violated in weak decays.

However, when I am doing a course problem on nuclear β-decay, then it still necessary to conserve parity.

2. Relevant equations

As an example, consider the
$La_{57} (J^P=2^-)$ → $Ce_{58} (J^P=0^+)$ decay, where I am asked to figure out what the angular momentum and spin state of the electron-neutrino system is.

3. The attempt at a solution

I get the right answer, when I require $l=1$ as this carries $P=-1$ and $S_{enu}=1$ to conserve angular momentum overall.

So my question is, why I am requiring parity to be conserved in nuclear β-decay when parity is violated for weak decays?

2. Mar 7, 2013

### Dick

Because parity is usually NOT violated. The exception doesn't make the rule. Even then it's not violated by much. Only certain cases in the quark mixing matrix will you get any significant violation at all. That's why it took till 1956 to discover. It's a perfectly fine approximate symmetry.

Last edited: Mar 7, 2013
3. Mar 8, 2013

### JoePhysicsNut

But in Wu's experiment, ALL the electrons come out in one direction making parity MAXIMALLY violated.

4. Mar 8, 2013

### Dick

Oh heck. I was thinking about CP violation. Different thing. Sorry!