How Do Quark-Antiquark Pairs Form Mesons in Electron-Positron Collisions?

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Discussion Overview

The discussion centers on the formation of quark-antiquark pairs in electron-positron collisions, specifically exploring the role of photons and gluons in this process. Participants examine Feynman diagrams and the implications of energy levels on the outcomes of such collisions, including the potential formation of mesons or jets of particles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Harry describes a Feynman diagram where a photon generated in an electron-positron collision becomes a quark-antiquark pair and questions whether this pair uses a gluon to form a meson.
  • One participant suggests that at low energies, the quark-antiquark pair could indeed become a meson, but at higher energies, they may separate and combine with additional quarks/antiquarks to form jets, introducing the concept of "three-jet events."
  • Another participant points out a discrepancy between a diagram in an A-level book showing two photons emitted at a 90-degree angle and the Feynman diagram where one photon creates a quark-antiquark pair, asking for clarification on the differences.
  • A later reply emphasizes that Feynman diagrams should not be interpreted literally, noting that they represent momentum rather than actual physical processes.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of Feynman diagrams and the outcomes of electron-positron collisions, indicating that multiple competing perspectives remain without consensus.

Contextual Notes

Some participants highlight the limitations of interpreting Feynman diagrams as direct representations of physical processes, suggesting a need for caution in understanding their implications.

HarryDaniels
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Edit, the title is electron, positron collision.
Sorry.

In the Feynmans Diagram involving a collision between a positron and a electron (or e+ and e-) a photon is generated and becomes a quark and anti-quark pair. Once these two are generate I know that one releases (radiates) a gluon. Can someone explain the formula and tell me whether or not this quark-antiquark pair use the gluon to become a meson?

Thank You
-Harry.
 
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HarryDaniels said:
Edit, the title is electron, positron collision.
Sorry.

In the Feynmans Diagram involving a collision between a positron and a electron (or e+ and e-) a photon is generated and becomes a quark and anti-quark pair. Once these two are generate I know that one releases (radiates) a gluon. Can someone explain the formula and tell me whether or not this quark-antiquark pair use the gluon to become a meson?

Thank You
-Harry.
Which formula are you asking about exactly?

In your example, for low energies, the quark and antiquark could become a meson, but at higher energies they would fly apart and combine with additional quarks/antiquarks (possibly created from ambient virtual photons, a.k.a. vacuum fluctuations) to become two distinct showers of particles, called jets. The emitted gluon can even separate from the quark and antiquark and produce a jet of its own. This is called a "three-jet event" (technical term :wink: no, really!) and it's frequently seen at large particle accelerators.
 


Sorry,
I was thinking of another formula.
 
Another Electron-positron collision

In my A-level book there is a diagram of an electron and a positron colliding and forming two EM radiation photons which go off at a 90 degree angle away from the direction in which the electron/positron hit. My problem is that in the Feynman Diagram an electron and a positron hit and one photon is created which becomes a quark anti quark pair.

Can someone explain to me why these are different?
 
first you should not think of Feynman diagrams of what is actually going on, the angles and lines etc are not REAL.

Thus the diagram in you A level book is repsenting the momentum arrows in the centre of mass frame for the electron (positron) and the photons.

Feynman diagram are something else.
 

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