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The Quark-Gluon Plasma

The Quark-Gluon Plasma. Marco van Leeuwen. Elementary particles. Standard Model: elementary particles. Quarks: Electrical charge Strong charge (color). up charm top down strange bottom. +anti-particles. Leptons: Electrical charge. electron Muon Tau n e n m n t.

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The Quark-Gluon Plasma

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  1. The Quark-Gluon Plasma Marco van Leeuwen

  2. Elementary particles Standard Model: elementary particles Quarks: Electrical charge Strong charge (color) up charm top down strange bottom +anti-particles Leptons: Electrical charge electron Muon Tau nenmnt photon EM force gluon strong force W,Z-boson weak force Force carriers: Atom Electronelementary, point-particle Protons, neutrons Composite particle  quarks EM force binds electronsto nucleus in atom Strong force binds nucleonsin nucleus and quarks in nucleons

  3. QCD and hadrons Quarks and gluons are the fundamental particles of QCD (feature in the Lagrangian) However, in nature, we observe hadrons: Color-neutral combinations of quarks, anti-quarks Baryon multiplet Meson multiplet S strangeness I3 (u,d content) I3 (u,d content) Mesons: quark-anti-quark Baryons: 3 quarks

  4. Seeing quarks and gluons In high-energy collisions, observe traces of quarks, gluons (‘jets’)

  5. How does it fit together? S. Bethke, J Phys G 26, R27 Running coupling: as decreases with Q2 Pole at m = L LQCD ~ 200 MeV ~ 1 fm-1 Hadronic scale

  6. Asymptotic freedom and pQCD At high energies, quarks and gluons are manifest At large Q2, hard processes: calculate ‘free parton scattering’ + more subprocesses

  7. Low Q2: confinement a large, perturbative techniques not suitable Bali, hep-lat/9311009 Lattice QCD: solve equations of motion (of the fields) on a space-time lattice by MC Lattice QCD potential String breaks, generate qq pair to reduce field energy

  8. QCD matter Energy density from Lattice QCD g: deg of freedom Nuclear matter Quark Gluon Plasma Bernard et al. hep-lat/0610017 Tc ~ 170 -190 MeV ec ~ 1 GeV/fm3 Deconfinement transition: sharp rise of energy density at Tc Increase in degrees of freedom: hadrons (3 pions) -> quarks+gluons (37)

  9. QCD phase diagram Quark Gluon Plasma (Quasi-)free quarks and gluons Temperature Critical Point Early universe Confined hadronic matter High-density phases? Elementary collisions (accelerator physics) Neutron stars Nuclear matter Bulk QCD matter: T and mB drive phases

  10. Heavy ion collisions Lac Leman Lake Geneva Geneva airport CERN Meyrin site Collide large nuclei at high energy to generate high energy density  Quark Gluon PlasmaStudy properties RHIC: Au+Au sNN = 200 GeV LHC: Pb+Pb √sNN≤ 5.5 TeV 27 km circumference

  11. Nuclear geometry: Npart, Nbin, L, e b y L Npart: nA + nB (ex: 4 + 5 = 9 + …) Nbin: nA x nB (ex: 4 x 5 = 20 + …) • Two limits: • - Complete shadowing, each nucleon only interacts once, s Npart • No shadowing, each nucleon interact with all nucleons it encounters, s  Nbin • Soft processes: long timescale, large s,stot Npart • Hard processes: short timescale, small s, stot Nbin Transverse view Density profile r: rpart or rcoll Eccentricity x Path length L, mean <L>

  12. Centrality examples ... and this is what you see in a presentation central peripheral mid-central This is what you really measure

  13. Centrality dependence of hard processes Total multiplicity: soft processes Binary collisions weight towards small impact parameter ds/dNch 200 GeV Au+Au • Rule of thumb for A+A collisions (A>40) • 40% of the hard cross section is contained in the 10% most central collisions

  14. Selected topics in Heavy Ions • Elliptic flow • Bulk physics, low pT, expansion driven by pressure gradients • Parton energy loss • High-energy parton ‘probes’ the quark gluon plasma • Light/heavy flavour

  15. Collective Motion Only type of collective transverse motion in central collision (b=0) is radial flow. Integrates pressure history over complete expansion phase Elliptic flow, caused by anisotropic initial overlap region (b > 0) More weight towards early stage of expansion (the QGP phase)

  16. Forming a system and thermalizing Animation: Mike Lisa 1) Superposition of independent p+p: momenta pointed at random relative to reaction plane b

  17. Forming a system and thermalizing Animation: Mike Lisa 1) Superposition of independent p+p: high density / pressure at center momenta pointed at random relative to reaction plane 2) Evolution as a bulksystem Pressure gradients (larger in-plane) push bulk “out” “flow” “zero” pressure in surrounding vacuum more, faster particles seen in-plane b

  18. How does the system evolve? N N   0 0 /4 /4 /2 /2 3/4 3/4 -RP (rad) -RP (rad) 1) Superposition of independent p+p: momenta pointed at random relative to reaction plane 2) Evolution as a bulksystem Pressure gradients (larger in-plane) push bulk “out” “flow” more, faster particles seen in-plane Animation: Mike Lisa

  19. Energy dependence of flow • Flow at RHIC consistent with ideal hydrodynamics!! … so what will we get at LHC ? NA49, PRC68, 034903

  20. Hard probes of QCD matter Use ‘quasi-free’ partons from hard scatterings Calculable with pQCD to probe ‘quasi-thermal’ QCD matter Quasi-thermal matter: dominated by soft (few 100 MeV) partons Interactions between parton and medium: • Radiative energy loss • Collisional energy loss • Hadronisation: fragmentation and coalescence Sensitive to medium density, transport properties

  21. Energy loss in QCD matter radiated gluon propagating parton m2 QCD bremsstrahlung(+ LPM coherence effects) Transport coefficient l Energy loss Energy loss probes: Density of scattering centers: Nature of scattering centers, e.g. mass: radiative vs elastic loss Or no scattering centers, but fields  synchrotron radiation?

  22. p0 RAA – high-pT suppression : no interactions RAA = 1 Hadrons: energy loss RAA < 1 : RAA = 1 0: RAA≈ 0.2 Hard partons lose energy in the hot matter

  23. Two extreme scenarios Scenario I P(DE) = d(DE0) Scenario II P(DE) = a d(0) + b d(E) 1/Nbin d2N/d2pT ‘Energy loss’ ‘Absorption’ p+p Downward shift Au+Au Shifts spectrum to left pT P(DE) encodes the full energy loss process Need multiple measurements to distentangle processes RAA gives limited information

  24. RAA at LHC GLV BDMPS T. Renk, QM2006 RHIC RHIC S. Wicks, W. Horowitz, QM2006 LHC: typical parton energy > typical E Expected rise of RAA with pT depends on energy loss formalism Nuclear modification factor RAA at LHC sensitive to radiation spectrum P(E)

  25. Summary • Elementary particles of the strong interaction (QCD): quarks and gluon • Bound states: p, n, p, K (hadrons) • Bulk matter: Quark-Gluon-Plasma • High T~200 MeV • Heavy ion collisions: • Produce and study QGP • Elliptic flow • Parton energy loss

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