Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Omega baryon decay

Tags:
  1. Sep 28, 2015 #1

    Garlic

    User Avatar
    Gold Member

    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. jcsd
  3. Sep 28, 2015 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    You cannot conserve energy and momentum at the same time if one particle decays to exactly one particle with a different mass.
     
  4. Sep 28, 2015 #3

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    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.
     
  5. Sep 28, 2015 #4

    Garlic

    User Avatar
    Gold Member

    Can't the electrons/electron neutrinos carry the momentum?
    And could a particle decay into another particle without rest if it had zero momentum?
     
  6. Sep 28, 2015 #5

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    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.
     
  7. Sep 28, 2015 #6

    Garlic

    User Avatar
    Gold Member

    The electron/neutrino comes from the weak decay that turns the strange quark into down quark, can't that electron/neutrino carry momentum?
     
  8. Sep 28, 2015 #7

    mfb

    User Avatar
    2016 Award

    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.
     
  9. Sep 28, 2015 #8

    arivero

    User Avatar
    Gold Member

    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.
     
  10. Sep 29, 2015 #9

    mfb

    User Avatar
    2016 Award

    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.
     
  11. Sep 29, 2015 #10

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    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 [itex]\Delta S = \Delta Q[/itex] rule. I'd be guessing 10^-12 or so.
     
  12. Sep 29, 2015 #11

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Oh right, there is no strong decay. Nevermind.
    Look at the invariant mass of the decay products.
     
  13. Sep 29, 2015 #12

    arivero

    User Avatar
    Gold Member

    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.

    mw2015fermionium.png
     
    Last edited: Sep 29, 2015
  14. Sep 29, 2015 #13

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Huh? The Sigma0 decays to Lambda + gamma. No pions.
     
  15. Sep 29, 2015 #14

    arivero

    User Avatar
    Gold Member

    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???
     
  16. Sep 29, 2015 #15

    arivero

    User Avatar
    Gold Member

    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).
     
  17. Sep 30, 2015 #16

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Neutrons are harder to detect than protons. Neutral pions are harder to detect than charged pions. The vast, vast majority of Lambdas are seen in the p-pi mode, not n-pi0. Indeed, the modern way to get rare Lambda decays is to look only at Lambdas from Sigma decay and use that as a kinematic constraint in the reconstruction.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook