Parity violation in weak decays

[JoePhysicsNut]

Homework Statement

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.

Homework 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.

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?

 

[Dick]

Homework Statement

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.

Homework 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.

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?

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.

 

[JoePhysicsNut]

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.

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

 

[Dick]

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

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

 

[paranormal]

Parity violation in weak decays refers to the fact that the weak interaction does not conserve parity symmetry, meaning that the mirror image of a particle and its antiparticle do not behave the same way under the weak force. This was first observed in Wu's experiment, where the beta decay of cobalt-60 showed a preference for electrons to be emitted in a certain direction, violating the expected symmetry.

However, this does not mean that parity is completely ignored in weak decays. In fact, parity conservation is still necessary in many cases, such as the nuclear beta decay that you mentioned. This is because while the weak interaction itself may not conserve parity, the overall interaction still needs to obey other conservation laws, such as angular momentum. In your example, requiring l=1 for the electron-neutrino system ensures that the overall angular momentum is conserved, even though parity is not.

So while parity violation in weak decays is an important concept in understanding the fundamental forces of nature, it does not mean that parity is completely disregarded in all cases. It is still necessary to consider other conservation laws in order to fully understand and predict the behavior of particles in these interactions.