R. Jakob

Linking parton distributions to form-factors and Compton scattering

Abstract. We relate ordinary and skewed parton distributions to soft overlap contributions to elastic form factors and large angle Compton scattering, using light-cone wave functions in a Fock state expansion of the nucleon. With a simple ansatz for the wave functions of the three lowest Fock states we achieve a good description of unpolarised and polarised parton distributions at large x, and of the data for the Dirac form factor and for Compton scattering, both of which can be saturated with soft contributions only. Large angle Compton scattering appears as a good case to investigate the relative importance of soft and hard contributions in exclusive processes which are sensitive to the end point regions of the nucleon wave function.

Generalized parton distributions from nucleon form factor data

Abstract.We present a simple empirical parameterization of the x- and t-dependence of generalized parton distributions at zero skewness, using forward parton distributions as input. A fit to experimental data for the Dirac, Pauli and axial form factors of the nucleon allows us to discuss quantitatively the interplay between longitudinal and transverse partonic degrees of freedom in the nucleon (“nucleon tomography”). In particular we obtain the transverse distribution of valence quarks at given momentum fraction x. We calculate various moments of the distributions, including the form factors that appear in the handbag approximation to wide-angle Compton scattering. This allows us to estimate the minimal momentum transfer required for reliable predictions in that approach to be around

The overlap representation of skewed quark and gluon distributions

\vert t\vert \simeq 3 {\rm GeV}^2

Asymmetries in polarized hadron production in

. We also evaluate the valence contributions to the energy-momentum form factors entering Ji’s sum rule.

e^{+}e^{-}

Within the framework of light-cone quantisation we derive the complete and exact overlap representation of skewed parton distributions for unpolarised and polarised quarks and gluons. Symmetry properties and phenomenological applications are discussed.

annihilation up to order 1/Q

We present the results of the tree-level calculation of inclusive two-hadron production in electron-positron annihilation via one photon up to subleading order in 1/Q. We consider the situation where the two hadrons belong to different, back-to-back jets. We include polarization of the produced hadrons and discuss azimuthal dependences of asymmetries. New asymmetries are found, in particular there is a leading cos(2 phi) asymmetry, which is even present when hadron polarization is absent, since it arises solely due to the intrinsic transverse momenta of the quarks

Leading asymmetries in two-hadron production in e^+e^- annihilation at the Z pole.

Abstract We present the leading unpolarized and single spin asymmetries in inclusive two-hadron production in electron-positron annihilation at the Z pole. The azimuthal dependence in the unpolarized differential cross section of almost back-to-back hadrons is a leading cos(2 φ ) asymmetry, which arises solely due to the intrinsic transverse momenta of the quarks. An extensive discussion on how to measure this asymmetry and the accompanying time-reversal odd fragmentation functions is given. A simple estimate indicates that the asymmetry could be of the order of a percent.

Skewed parton distributions in real and virtual compton scattering

The handbag contribution to Compton scattering at moderately large momentum transfer factorises into parton-photon subprocess amplitudes and new form factors representing 1/x-moments of skewed parton distributions. A detailed phenomenological study for polarised and unpolarised real and virtual Compton scattering is presentedAbstract The handbag contribution to Compton scattering at moderately large momentum transfer factorises into parton-photon subprocess amplitudes and new form factors representing 1/ x -moments of skewed parton distributions. A detailed phenomenological study for polarised and unpolarised real and virtual Compton scattering is presented.

Accessing transversity with interference fragmentation functions

We discuss in detail the option to access the transversity distribution function

Interference fragmentation functions in electron-positron annihilation

{h}_{1}(x)