# Omega baryon decay

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1. Sep 28, 2015

### Garlic

Hello,
Why is there a decay mode of omega baryon that creates unnecessary particles? sss -> uds + u(bar)s and why not just sss -> dss ?

2. Sep 28, 2015

### Staff: Mentor

You cannot conserve energy and momentum at the same time if one particle decays to exactly one particle with a different mass.

3. Sep 28, 2015

### Orodruin

Staff Emeritus
First of all, you can never have a one-to-one decay as this violates conservation of energy. You would need to have additional particles radiated.

Second, there is no interaction which transforms an s-quark into a d-quark. Quark flavour is only broken by charged current weak interactions, in this case converting an s into a u and a W boson, the W boson then couples to the ubar-d pair.

4. Sep 28, 2015

### Garlic

Can't the electrons/electron neutrinos carry the momentum?
And could a particle decay into another particle without rest if it had zero momentum?

5. Sep 28, 2015

### Orodruin

Staff Emeritus
Then you have additional particles that you need to create. Why do you think that would be simpler than going to a baryon and a meson?

No.

6. Sep 28, 2015

### Garlic

The electron/neutrino comes from the weak decay that turns the strange quark into down quark, can't that electron/neutrino carry momentum?

7. Sep 28, 2015

### Staff: Mentor

That could be another possible decay, didn't check it in detail. In general, every possible decay happens, just the branching fractions differ.

Edit: It is, but the decay to $\Lambda K$ is much more frequent.

8. Sep 28, 2015

### arivero

My favorite baryon decay is Sigma0, mass 1192, goes gamma + Lambda, mass 1116, and then Lambda goes neutron + pion, or proton + pion.

Quark content is the same: uds. Spin and parity, the same too, 1/2+.

But sigma0 can not go directly to neutron + pion, or has not been measured doing it.

9. Sep 29, 2015

### Staff: Mentor

It is strange that the PDG does not even list an upper limit. It looks like an obvious decay channel to search for.

10. Sep 29, 2015

Staff Emeritus
A. How would you do this experiment?
B. What sort of BF would you expect? Remember, this is a weak decay competing with an electromagnetic decay. Also, it violates the $\Delta S = \Delta Q$ rule. I'd be guessing 10^-12 or so.

11. Sep 29, 2015

### Staff: Mentor

Oh right, there is no strong decay. Nevermind.
Look at the invariant mass of the decay products.

12. Sep 29, 2015

### arivero

Well, the same experiment which is measuring the decay to Lambda surely is already measuring its pion distribution, so it could look for pions happening with a different one. For the branching ratio, I'd go more on the 10^-9 or 10^-10, but well, this is the goal of publishing limits, isn't it?

Let me attach as reference one of my traditional plots of total decay width vs mass, as a guide for estimates. it could be remarked that there is some help from QCD in the electromagnetic decays: the blue an green parallel lines are the scaling of orto and parapositronium, the light blue is where electromagnetic decays of mesons actually live.

Last edited: Sep 29, 2015
13. Sep 29, 2015

Staff Emeritus
Huh? The Sigma0 decays to Lambda + gamma. No pions.

14. Sep 29, 2015

### arivero

I understood that yout question was how to measure the limit of in-existence of this decay. So your estimate of 10^-12 was not for this branch ratio???

15. Sep 29, 2015

### arivero

Ah ok, I see the misunderstanding. What I mean is that any experiment Sigma-->Lambda will surely measure the Lambda by detecting its decay to pion + nucleon. So if a direct -very exceptional- decay from Sigma to nucleon + pion happens, it should be recorded in the same detectors. They could do some selection on absence of gamma, or just refine the analysis of the distribution of pions (and nucleons).

16. Sep 30, 2015