# Decay rho->eta + pion is forbidden.why?

1. Oct 30, 2009

### nur.alifah

decay rho-->eta + pion is forbidden.why?

is it only violation of charge conjugate or its not conserve the energy & momentum.

2. Oct 30, 2009

Staff Emeritus
Re: decay rho-->eta + pion is forbidden.why?

It violates G-parity.

C is not a good symmetry for charged particles.

3. Oct 30, 2009

### Norman

Re: decay rho-->eta + pion is forbidden.why?

To expand a bit on this (and please feel free to correct me if I am wrong), G-parity is conserved in strong interactions but not in weak or electromagnetic. So, $$\rho \rightarrow \pi\pi$$ dominates the decay of a rho since it is a strong decay, but the decay $$\rho \rightarrow \eta \pi$$ should still be allowed for a weak process, albeit suppressed in comparison to the 2 pion channel due to phase space considerations.

4. Oct 30, 2009

Staff Emeritus
Re: decay rho-->eta + pion is forbidden.why?

Yes, but weak decays are suppressed by the couplings. You'll be down 10, 12 maybe 15 orders of magnitude. The small isospin violation in the strong interaction is probably more important.

5. Oct 30, 2009

### nur.alifah

Re: decay rho-->eta + pion is forbidden.why?

the strangeness is conserve,
so,is it only the isospin violate make this decay forbidden?

6. Nov 1, 2009

### clem

Re: decay rho-->eta + pion is forbidden.why?

It is only the G parity. The decay occurs via the EM interaction, with an intermediate virtual photon.