Presentation on theme: "Parton Model & Parton Dynamics Huan Z Huang Department of Physics and Astronomy University of California, Los Angeles Department of Engineering Physics."— Presentation transcript:
Parton Model & Parton Dynamics Huan Z Huang Department of Physics and Astronomy University of California, Los Angeles Department of Engineering Physics Tsinghua University Oct 2006 @ Tsinghua
Quantum Chromodynamics QCD: Field Theory of strong interaction in matter SU flavor (3) X SU color (3) Confinement: No free quarks, gluons (so-called partons) Color singlet Hadrons: meson baryon
Momentum Scale and Position Resolution P x > hc ~ 200 MeV fm
Rutherford Hofstadter SLAC FNAL CERN HERA Discoveries New Machine and Energy Frontier Discovery
Exploring nuclear structure - elastic electron-nucleus scattering l Scattering of electron (Spin 1/2) on point- charge charge (Spin 0): Mott cross-section l Take into account finite charge distribution: Form factor Ignore recoil! 12 C Hofstadter, 1953
fraction of the proton momentum carried by the charged parton fraction of the electron energy carried by the virtual photon ( inelasticity ) (mass) 2 of * p system center of mass energy of ep system (momentum transfer) 2 virtuality of *, Z 0, W ( size of the probe) -1 Kinematic Variables
Exploring the Proton structure - inelastic ep scattering Friedman, Kendall and Taylor l Scattering of electron (Spin 1/2) on proton (Spin 1/2) Deep-inelastic scattering (DIS) Nobel Prize 1990 Scattering on point- like objects: Quarks!
Structure Functions Structure function measurement: Formalism –In terms of laboratory variables: –Formulate this now in relativistic invariant quantities: –Instead of W 1 and W 2, use: F 1 and F 2 : Longitudinal structure function: F L
Parton Model Interpretation of F 2 ) Isospin Symmetry
Spin Physics Program The Spin Structure of the Proton: ½ = ½ q + G + q up, down and strange quarks G gluons L angular momentum of quarks and gluons Experimentally: 1) total spin in quarks ~ 30% 2) sea quarks are polarized too 3) little info about the gluon polarization 4) even less know about and how to measure
RHIC Spin Physics At RHIC we use polarized p+p collisions to study 1)Gluon spin structure function q+g q+ 2)Sea quark spin structure function q+q W boson 3)Quark transverse spin distribution Essential to measure photons, electrons and jets ! STAR: TPC and Electromagnetic Calorimeter- Lead/Plastic Scintillator sandwich, Shower Max Detector for electron/hadron separation.
QCD Masses Dominate !! Proton Mass ~ 940 MeV three quarks uud each quark ~ 300 MeV Pion two quarks: Mass ~ 140 MeV, spin=0 Rho meson (same quark content as pion): Mass ~ 776 MeV Very large component of the mass from Interactions The Interaction energy strongly spin-dependent !