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Quark Structure and RHIC Highlights

Quark Structure and RHIC Highlights

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Quark Structure and RHIC Highlights

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  1. Quark Structure andRHIC Highlights Abby Bickley University of Colorado July 8, 2005

  2. Standard Model: Particles • Provides a description of the fundamental particles and forces that govern matter • Quarks and leptons as identified as the elementary particles • Each quark and lepton has an antimatter partner which is referred to as an antiquark or antilepton

  3. Elementary Particles: Quarks • Spin 1/2 fermions • Exist in the bound state as hadrons • Baryon: 3 bound quarks • Meson: 2 bound quarks • Never observed in isolation • Naturally occur in three families

  4. Elementary Particles: Quarks • We know that the nucleus of an atom is composed of nucleons (protons & neutrons) • But these nucleons also have a quark substructure • Proton = uud • Neutron = udd • The antimatter equivalent to the proton is the antiproton (uud) • The most common mesons are pions and kaons +: ud, -: ud, K+: us, K-: us

  5. Elementary Particles: Leptons • Spin 1/2 fermions • Point-like => no substructure • Never bound

  6. Standard Model - Forces • Standard model includes the forces that govern the interactions between matter • Each force is conveyed by a mediating (or exchange) particle • Weak force governs radioactive decay • Strong force binds quarks in hadrons and nucleons in the nucleus • Gravitational force has not yet been incorporated into the standard model

  7. Quantum Chromodynamics • Theory that describes the properties of the strong force • Color = property associated with interaction (analogous to electric charge) • Every quark carries a color charge of red or green or blue • Every gluon (exchange particle) also carries a color charge • Results in important consequences for RHIC

  8. Quantum Chromodynamics • Coupling between color carriers INCREASES with distance • (opposite behavior to the more familiar electromagnetic force) • Confinement: • At large distances the QCD potential is large and confines quarks inside bound state  it is not possible to separate bound quarks • Asymptotic Freedom: • At very small distances the QCD potential is weak and quarks behave as if they are unbound

  9. Confinement • The energy required to pull apart a quark antiquark pair is greater than the rest mass of the pair • As energy is introduced to the system a new quark antiquark pair will be produced from the vacuum instead of separating the original pair

  10. Asymptotic Freedom • Quarks behave as if they are unbound or free when separated by only very small distances • Theory tells us that it might be possible to achieve this state in systems of extreme temperature and/or density • It is this deconfined state that is known as the Quark Gluon Plasma (QGP) • Conceptually the QGP can be visualized as a soup of freely moving quarks and gluons

  11. H2O Nuclear Matter Critical Point 225 Quark Gluon Plasma Liquid 170 Pressure (atm) Phase Transition Solid Gas Hadron Gas Temperature (MeV) 0.006 Triple Point Neutron Stars Nuclei 0 1 0.01 374 Temperature (C) Baryochemical Potential (GeV) 170 MeV ~ 2 x 1012 C Phase Diagrams of Matter

  12. Cosmology

  13. Time Initial Geometry Parton Production Hadron Formation Chemical Freezeout Thermal Freezeout 0 fm/c ~2 fm/c ~7 fm/c >7fm/c Characterized by alignment of colliding nuclei. Collision Evolution 1 fm/c ~ 3x10-24 seconds

  14. Time Initial Geometry Parton Production Hadron Formation Chemical Freezeout Thermal Freezeout 0 fm/c ~2 fm/c ~7 fm/c >7fm/c Quarks and gluons generated; Rescattering may lead to thermal equilibrium. Collision Evolution 1 fm/c ~ 3x10-24 seconds

  15. Time Initial Geometry Parton Production Hadron Formation Chemical Freezeout Thermal Freezeout 0 fm/c ~2 fm/c ~7 fm/c >7fm/c Collision Evolution Quarks and gluons combine to form particles, but inelastic collisions continue. 1 fm/c ~ 3x10-24 seconds

  16. Time Initial Geometry Parton Production Hadron Formation Chemical Freezeout Thermal Freezeout 0 fm/c ~2 fm/c ~7 fm/c >7fm/c Collision Evolution Inelastic collisions cease; Final particle yields fixed. 1 fm/c ~ 3x10-24 seconds

  17. Time Initial Geometry Parton Production Hadron Formation Chemical Freezeout Thermal Freezeout 0 fm/c ~2 fm/c ~7 fm/c >7fm/c Collision Evolution Elastic collisions cease; Particles travel to detector. 1 fm/c ~ 3x10-24 seconds

  18. QGP Signals: J/ Suppression • J/ suppression • J/ particle is a meson consisting of a cc pair • Commonly referred to as hidden charm • Color screening = dynamic screening of long range confining potential in the medium • End result of color screening is the reduction of the number of J/ particles produced in the collision • Consequently an enhancement in the number of open charm particles might be expected

  19. QGP Signals: J/ Suppression • J/ particle can not be measured directly since it’s half life is too small • Must instead measure its decay products J/  e++ e- BR = 6% J/   ++ - BR = 6% • These can be measured in the PHENIX central arm detectors (RICH & EMC) and muon arm detectors, respectively • Compare results from very heavy dense systems with lighter less dense collisions • Measure as a function of collision centrality

  20. QGP Signals: J/ Suppression • First Au+Au 200 GeV collision data taken in the fall of 2001 • PHENIX collected ~50 Million minimum bias events • Suggestive of suppression but limited by insufficient statistics

  21. QGP Signals: Jet Suppression • Hard scattering processes lead to the emission of high energy sprays of back to back particles • One of these jets must pass through the bulk of the medium in order to be detected • In the presence of a QGP expect “away side” jet to be suppressed relative to the “near side” jet

  22. Probes of the Medium Sometimes a high energy photon is created in the collision. We expect it to pass through the plasma without pause.

  23. Probes of the Medium Sometimes we produce a high energy quark or gluon. If the plasma is dense enough we expect the quark or gluon to be swallowed up.

  24. Jet correlations in proton-proton reactions. Strong back-to-back peaks. Jet Quenching ! Azimuthal Angular Correlations

  25. Jet correlations in central Gold-Gold. Away side jet disappears for particles pT > 2 GeV Jet correlations in proton-proton reactions. Strong back-to-back peaks. Jet Quenching ! Azimuthal Angular Correlations

  26. Jet correlations in central Gold-Gold. Away side jet reappears for particles pT>200 MeV Jet correlations in proton-proton reactions. Strong back-to-back peaks. Jet correlations in central Gold-Gold. Away side jet disappears for particles pT > 2 GeV Jet Quenching ! Azimuthal Angular Correlations

  27. Superfluidity & RHICaka “The Perfect Liquid”

  28. Properties of Superfluidity? • Ideal superfluid: • Viscosity of the fluid is zero • Experiences no resistance to flow • Only hypothetically possible at absolute zero where no excitations exist • Real superfluid: • Characterized as a two-fluid system • Superfluid component - fraction of liquid in ground state • Normal component - fraction of liquid in excited state; experiences finite viscosity

  29. Example 1: 4He • Observation: • Early 1930’s => liquid state does not solidify as absolute zero is approached • Late 1930’s => below the temperature of 2.17 K resistance to flow decreases by a factor of >1500 • Explanation: • Obeys Bose statistics • Wavefunction of system is symmetric to the exchange of any two atoms • A finite fraction of the atoms occupy a single one particle state • Superfluid component is a Bose-Einstein Condensate • Normal component carries the entropy of the system

  30. Example 2: 3He • Observation: • Pre-1970 => liquid state does not solidify as absolute zero is approached • Early 1970’s => below the temperature of 3 mK three distinct phases exist that exhibit properties of superfluidity • Explanation: • Obeys Fermi statistics • Fermions pair up into Cooper pairs • “a sort of giant diatomic quasi-molecule whose characteristic ‘radius’ is very much larger than the typical interatomic distance” • Cooper pairs obey Bose statistics and undergo Bose-Einstein Condensation

  31. Viscosity Bound • Recent work by Son et al. has shown that a lower viscosity bound may exist even in superfluids • Finite viscosity results from normal component hep-th/0405231

  32. Relevance to RHIC • Hydrodynamics can be used to describe the collision medium formed in a heavy ion collision • A hydro representation is favored over perturbative calculations by the strong collective effects observed • The viscosity of the collision system results in a deviation in the observed particle distributions relative to that predicted by hydro • Figure shows deviation of measured elliptic flow from hydro predictions

  33. Relevance to RHIC • Model estimates of the viscosity of QGP very small • (/s) ~1/10 • (/s) >1 for water • Heavy ion collision system formed at RHIC could be used to test the viscosity bound • How could QGP be considered a superfluid???? • In a strongly coupled system bound pairs of quarks and gluons could be formed and experience analogous properties to Cooper pairs

  34. References • Leggett, A.J., Reviews of Modern Physics, Vol. 71, No. 2, Centenary 1999. • Wilks, J., “The Theory of Liquid 4He”, www.iop.org/EJ/article/0034-4885/20/1/302/rpv20i1p38.pdf • Shuryak, E., hep-ph/0312227