The Unexpected Role of Final State Interactions in Deep Inelastic Scattering

Rescattering of the struck quark in Deep Inelastic Scattering implies that measured parton distributions are not directly related to the Fock state probabilities of the target wave function. The production amplitudes acquire dynamical phases, which gives rise to shadowing and diffraction in DIS. I review the kinematics and dynamics of DIS as seen in various frames and gauges.Comment: 11 pages, 6 figures. Talk at the "International Conference: I. Ya. Pomeranchuk and Physics at the Turn of the Centuries", Moscow, January 200

Duality in Semi-Exclusive Processes

Bloom-Gilman duality relates parton distributions to nucleon form factors and thus constrains the dynamics of exclusive processes. The quark electric charge dependence implies that exclusive scattering is incoherent on the quarks even at high momentum transfers. Data on semi-exclusive meson production exceeds the duality prediction by more than an order of magnitude and violates quark helicity conservation. This suggests that the subprocess is dominated by soft `endpoint' contributions which obey dimensional scaling. The large transverse size of the subprocess may explain the absence of color transparency in fixed angle processes.Comment: Talk at the ``Workshop on Exclusive Processes at High Momentum Transfer'' at Jefferson Laboratory, Newport News, USA (May 2002). 7 page

Measuring transverse size with virtual photons

Fourier transforming the virtual photon transverse momentum in \gamma*(q)+N \to f processes allows new insight into hadron dynamics as a function of impact parameter b. I discuss how previous analyses of charge density based on elastic and transition form factors (f=N, N*) can be generalized to any multi-hadron final state (f=\pi N, \pi\pi N, \bar D \Lambda_c,...). The b-distribution determines the transverse positions of the quarks that the photon couples to, and can be studied as a function of multiplicity, the relative transverse momenta, quark masses and polarization. The method requires no factorization nor leading twist approximation. Data with spacelike photon virtualities in the range 0 1/Q_{max} in impact parameter.Comment: Talk at the Third International Workshop on Transverse Polarization Phenomena in Hard Scattering (Transversity 2011), in Veli Losinj, Croatia, 29 August - 2 September 2011. 7 page

Parton Propagation in a Gluon Field

The phenomenological success of PQCD is based on processes where the effects of the color field environment on parton propagation can be eliminated or is universal. In hard diffraction and quarkonium production the PQCD subprocess is the same as in fully inclusive scattering, but the sensitivity to reinteractions is different. I discuss how this may be exploited to give new information on the dynamics of hard collisions.Comment: Talk at Workshop on In-Medium Hadron Physics, University of Giessen, November 2004. 10 pages, 5 figure

Summary Talk on Quark-Hadron Duality

I ascribe the origin of Bloom-Gilman duality in DIS to a separation of scales between the hard subprocess and soft resonance formation. The success of duality indicates that the subprocesses of exclusive form factors are the same as in DIS. The observed dominance of the longitudinal structure function at large x in \pi N \to \mu^+\mu^- X can explain why local duality works for DIS with a pion target. The failure of duality in semi-exclusive processes indicates that high momentum transfer t is not sufficient to make the corresponding subprocesses compact.Comment: 8 pages, 5 figures. Summary talk at the First Workshop on Quark-Hadron Duality and the Transition to pQCD, Frascati, 6-8 June 200