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Color flow of quarks and gluons in high-energy collisions

Color flow of quarks and gluons in high-energy collisions. Maarten Buffing (VUA) Track: theoretical physics Amsterdam master of physics symposium April 29, 2011. Content. Introduction to QCD and color High-energy collisions Theory: phases Importance to experiments Conclusion and outlook.

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Color flow of quarks and gluons in high-energy collisions

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  1. Color flow of quarks and gluons in high-energy collisions Maarten Buffing (VUA) Track: theoretical physics Amsterdam master of physics symposium April 29, 2011

  2. Content • Introduction to QCD and color • High-energy collisions • Theory: phases • Importance to experiments • Conclusion and outlook

  3. QCD • Standard Model • Internal structure of proton • Focus on quarks and gluons Leptons: Quarks: Gauge bosons: Proton

  4. QCD • Standard Model • Internal structure of proton • Focus on quarks and gluons Leptons: Quarks: Gauge bosons: Proton

  5. Color • QCD has color charges (cc’s) forming a symmetry group • There exist 3 cc’s and 3 anti-cc’s • All observables are colorless Feynman diagram description: Quarks: Gluons:

  6. Color • QCD has color charges (cc’s) forming a symmetry group • There exist 3 cc’s and 3 anti-cc’s • All observables are colorless Feynman diagram description: Quarks: Gluons:

  7. Colorflow (1) • Quark-quark-gluon vertices give rise to multiple color flows • Singlet gluon contributions must be subtracted

  8. Colorflow (2) • In Feynman diagrams, multiple color flows contribute • Consider qq-scattering with two gluons as an example

  9. Colorflow (2) • In Feynman diagrams, multiple color flows contribute

  10. Collisions (1) • Consider quark-quark scattering • Toy model: no color exchange

  11. Collisions (2) • Implications for the cross-section of high energy collisions even in the case of no color exchange • Distribution functions • Fragmentation functions Δ

  12. Collisions (2) • Implications for the cross-section of high energy collisions even in the case of no color exchange • Distribution functions • Fragmentation functions Δ

  13. Collisions (2) • Implications for the cross-section of high energy collisions even in the case of no color exchange • Distribution functions • Fragmentation functions Δ

  14. Collisions (3) • Additional leading gluons need to be considered, for instance: • They complicate color flow • Color entanglement T.C. Rogers, P.J. Mulders (2010)

  15. Collisions (3) • Additional leading gluons need to be considered, for instance: • They complicate color flow • Color entanglement T.C. Rogers, P.J. Mulders (2010)

  16. Theory: phases (1) • Color entanglement spoils factorization

  17. Theory: phases (2) • Enormous amount of contributing Feynman diagrams: lots of mathematics • Example: a number of three gluon contributions

  18. Importance to experiments • It turns out that summation of all diagrams with arbitrary number of gluons gives phases • The phases save color-gauge invariance • Non-trivial experimental effects in transverse plane for certain polarisations

  19. Conclusion and outlook • Color flow is relevant for the understanding of high-energy collisions in specific observables • Inclusion of all possible diagrams assures color-gauge invariance and gives rise to novel features • M.G.A. Buffing, P.J. Mulders, “Gauge links for Transverse Momentum Dependent Correlators at tree-level” (will appear on the Archive soon)

  20. Backup slides

  21. Transverse momentum • Decomposition of quark momentum: Proton

  22. Preventing double counting • Certain diagrams are identical, for example:

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