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

Definition of short- and long-distance effects in branching ratios

  1. Aug 21, 2008 #1
    Would somebody be kind enough to explain what exactly is meant when discussing short- or long-distance contributions/effects to branching ratio calculations?
     
  2. jcsd
  3. Aug 21, 2008 #2

    blechman

    User Avatar
    Science Advisor

    Hmmm.... I think it depends on the context. For example, something I've been thinking about recently for my research: in K-Kbar mixing in the Standard Model, you can have effects from heavy quarks and light quarks running through loops. The heavy quarks are highly virtual (such as the top and charm) and so, thanks to the asymptotic freedom of QCD, these contributions are perturbative. However, the contribution from the light quark masses (up) is definitely not perturbative, since these quarks are quite light and are not "as virtual" as the heavy quarks. This means that they can exist longer from the uncertainty principle, and this means that the contributions from light quarks is ACTUALLY a contribution from pions, the IR limit of QCD. These are called "long-distance" contributions, and cannot be computed with perturbative QCD.

    Hope that helps.
     
  4. Aug 21, 2008 #3
    Perfect. That was exactly the explanation I was looking for. Thanks blechman
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Definition of short- and long-distance effects in branching ratios
  1. Higgs Branching Ratios (Replies: 2)

Loading...