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The Big Picture

The Big Picture. George Smoot. Particle Production in Heavy Ion Collisions. pQCD Strings Thermal models Hydrodynamics … Overview of results from different approaches. Standard Model. Steven Weinberg. Abdus Salam. Sheldon Glashow. Beta decay, Neutrino scattering. d  u.

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The Big Picture

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  1. The Big Picture George Smoot

  2. Particle Production in Heavy Ion Collisions • pQCD • Strings • Thermal models • Hydrodynamics • … • Overview of results from different approaches

  3. Standard Model Steven Weinberg Abdus Salam Sheldon Glashow

  4. Beta decay, Neutrino scattering d  u

  5. Fathers of QCD George Zweig  biology hedge funds Murray Gell-Mann

  6. QCD • Psi_n: Quarks • A_mu: Gluon Field • F_mu nu: Gluon field tensor • m_n: Quark masses • t_a: Gell-Mann Matrices/2 • a: Gluon Colour index (1..8)

  7. Parts of the Lagrangian • , C are the SU(3) structure constants • , like in QED, but with non-commutative part • , quark couple to gluons through color current

  8. Invention of color: Omega, Delta-, Delta++ Yoichiro Nambu

  9. How do we know there are quarks and colours? • Deep inelastic scattering experiments:direct observation of Rutherford scattering off the quarks • Measured cross section for hadron production in e+ + e- interactions

  10. 2 e- f s ~ gamma* fbar e+ ~ charge (f) ~ charge (e)

  11. Our prediction for the number of quarks and colours…

  12. Cross section e+e-  hadrons E_CM (GeV)

  13. Ratio R

  14. Discovery of charm (74), bottom (77) and top (95) Sam Ting (the J in J/Psi) Luciano Maiani, predicted charm to avoid flavour changing currents Makoto Kobayashi, pred. bottom for CP violation Toshihide Maskawa pred. bottom for CP violation Leon Ledermann “Ups-Leon”

  15. Hadron structure (I) • To first approximation: three quarks (baryon) or quark--anti-quark (meson) • Calculated as irreducible representationsof SU(n). E.g. with help of Young Tableaux(see e.g. W. Greiner, Symmetries) • First realized by Gell-Mann (quarks) (PRL, Eightfold Way, Nobel prize) and Zweig (aces).(Zweig’s paper is still pre-print and never got accepted for publication ;-) …)

  16. Quarks couple to hadrons

  17. Hadron structure (II) • Hadrons are complicated objects of many quarks and gluons (partons) • We know this from the momentum distribution of the partons in the hadrons(measurements by HERMES etc…) • The number of partons in a hadron depends on the resolution (i.e. momentum transfer, usually called Q).

  18. Parton model He who needs not be explained James Bjorken

  19. Sets of PDFs • CTEQ, from the CTEQ Collaboration • GRV, from M. Glück, E. Reya, and A. Vogt • GJR, from M. Glück, P. Jimenez-Delgado, and E. Reya • MRST, from A. D. Martin, R. G. Roberts, W. J. Stirling, and R. S. Thorne  new dev., generalized pdf’s

  20. The pQCD scattering cross section Within perturbative QCD a scattering process can be easily described on the basis of the parton distribution functions and the pQCD scattering cross section

  21. Running coupling constant, asymptotic freedom Frank Wilzcek Mark Alford Krishna Rajagopal David Gross Wilzcek Witten Pisarski

  22. Why can we use pQCD? The QCD coupling constant decreases with increasing momentum transfer (i.e. at small distances) Typical Q for alpha~1, is Q~200 MeV, i.e. 1fm

  23. Hadronization of a quark (gluon jet) • pQCD only describes the scattering of the parton, not the hadronization process • I.e. the pQCD scattering formula needs to be supplemented with a model for the ‘fragmentation’ of the parton (the parton shower or the jet, resp) • This function is called the fragmentation function Dqh(z), with z being the fraction of the total parton momentum given to the hadron

  24. e- q gamma* qbar e+ Back to e+e- • The fragmentation of a jet is easiest understood in the simple process:e+e-  q qbar hadrons

  25. Lattice people Micheal Creutz

  26. More lattice people Fritjof Karsch Zoltan Fodor Owe Philipsen

  27. Linear potential from lattice

  28. If the quarks travel away from each other the QCD potential leads to particle production in the critical field

  29. Understanding the q-qbar system • We expect the production of new q-qbar pairs from the decay of the critical vacuum between the quarks  q….qbar-q….qbar-q….qbar-q….qbar-q…qbar

  30. rotator model of the hadron (I) • Motivated by the behaviour of angular momentum vs. mass J J(M2)=alpha(0)+alpha’ M2 alpha(0) = Regge interceptalpha’ = Regge slope ~ 1 GeV-2 M2

  31. Rotator (II) Model hadron as two (massless) color charges moving at the speed of light on a circle r

  32. String tension estimate

  33. Lattice results color electric and magnetic Flux tube between quarks and anti-quarks 22 lattice spacing apart

  34. Particle production: Tunneling A(z) 0 z L I II III

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