Feynman diagram of secondary Sigma plus decay

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SUMMARY

The discussion focuses on the Feynman diagram for Sigma plus decay into a positive pion and a neutron, specifically analyzing the decay processes of uus to uud plus ddbar and uus to udd plus udbar. The participants clarify that the branching fractions (BFs) for the decay into a neutral pion and a proton, as well as a positive pion and a neutron, are not equal but rather 52/48. They highlight the role of photon/gluon emissions in the creation of down quark pairs and discuss the implications of angular distributions related to the decay angles of the particles involved.

PREREQUISITES
  • Understanding of Feynman diagrams and particle decay processes
  • Familiarity with quark interactions and flavor-changing neutral currents (FCNC)
  • Knowledge of branching fractions in particle physics
  • Basic concepts of quantum chromodynamics (QCD) and gauge bosons
NEXT STEPS
  • Study the implications of flavor-changing neutral currents in particle decays
  • Explore the role of photon and gluon emissions in quark pair production
  • Investigate the significance of angular distributions in particle decay processes
  • Learn about the differences in mass and decay properties between neutrons, protons, and pions
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Particle physicists, students studying quantum mechanics, and researchers interested in the intricacies of quark interactions and decay processes.

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Can someone describe the Feynman diagram for the Sigma plus decay to a positive pion and a neutron? I'm fine with the primary decay to the neutral pion and a proton. There appears to be insufficient down quarks created.
 
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uus > ud~ u d d

Well one d d~ set can be made with a photon/gluon, while the s-> d can be a loop-level FCNC.

OR

uus : s---u
uus : u---d
via a W exchange, and the d dbar pair is made with a photon/gluon emission.
 
Look at the BF's - they are equal for p pi0 and n pi+, so we're not talking about FCNC loops.

You have uus --> uud + ddbar (p pi0)
and uus --> udd + udbar (n pi+)

This is just a rearrangement, which explains their equality.
 
Thanks guys. The BF's are actually not 50/50 but 52/48. Why should they be slightly different? Does the fact that alpha for p pi0 (36 deg) and for n pi+ (167 deg) relevant for this? Appreciate your comments.
 
The masses aren't identical for n and p, nor pi+ and pi0.
 

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