The strange-sea quark spin distribution in the nucleon from inclusive and semi-inclusive deep-inelastic scattering

We propose new method which allows determination of the strange-sea quark spin distribution in the nucleon through measurement of various inclusive and semi-inclusive polarized deep inelastic electron- or muon-proton reactions. It is shown, that using combinations of inclusive data and semi-inclusive data containing neutral pions in the final state, it is possible to extract the strange-sea quark spin distribution. Similar result can be obtained for charged pions and some other hadrons also

Higher Twist Effects in Deep Inelastic Scattering on Nuclei

Particle production in deep inelastic scattering on nuclei is reduced due to absorption of the produced particles in the nucleus. The photon ejects a quark from a bound nucleon which propagates through the nucleus forming a prehadron before turning into a hadron. We calculate the higher twist effect in hadronization which dominates the $z \to 1$ region of fragmentation.Comment: Based on a talk given by H.J. Pirner at the Fifth International Conference on Perspectives in Hadronic Physics, Trieste, May 200

Deep Exclusive Scattering and Generalized Parton Distributions : Experimental Review

Since the Generalized Parton Distribution theoretical framework was introduced in the late 90's, a few published and numerous preliminary results from Deep Exclusive Scattering (DES) have been extracted from non-dedicated experiments at HERA and Jefferson Lab. We review most of these results, comment on the ongoing dedicated research in this topic and conclude with the expectations from the next generation of experiments in the near future.Comment: 10 pages, 8 figures, Baryons '04 proceeding

An introduction to the Generalized Parton Distributions

The concepts of Generalized Parton Distributions (GPD) are reviewed in an introductory and phenomenological fashion. These distributions provide a rich and unifying picture of the nucleon structure. Their physical meaning is discussed. The GPD are in principle measurable through exclusive deeply virtual production of photons (DVCS) or of mesons (DVMP). Experiments are starting to test the validity of these concepts. First results are discussed and new experimental projects presented, with an emphasis on this program at Jefferson Lab.Comment: 5 pages, 3 figures Proc. Int. Conf. on Quark Nuclear Physics (QNP2002), to be published in Eur. Phys. Jour.

Time Dependent Hadronization via HERMES and EMC Data Consistency

Using QCD-inspired time dependent cross sections for pre-hadrons we provide a combined analysis of available experimental data on hadron attenuation in DIS off nuclei as measured by HERMES with 12 and 27 GeV and by EMC with 100 and 280 GeV lepton beam energies. We extract the complete four-dimensional evolution of the pre-hadrons using the JETSET-part of PYTHIA. We find a remarkable sensitivity of nuclear attenuation data to the details of the time-evolution of cross sections. Only cross sections evolving linearly in time describe the available data in a wide kinematical regime. Predictions for experimental conditions at JLAB (5 and 12 GeV beam energies) are included.Comment: version as publishe

Radial excitations of Q-balls, and their D-term

We study the structure of the energy-momentum tensor of radial excitations of Q-balls in scalar field theories with U(1) symmetry. The obtained numerical results for the $1\le N \le 23$ excitations allow us to study in detail patterns how the solutions behave with N. We show that although the fields and energy-momentum tensor densities exhibit a remarkable degree of complexity, the properties of the solutions scale with N with great regularity. This is to best of our knowledge the first study of the D-term d1 for excited states, and we demonstrate that it is negative --- in agreement with results from literature on the d1 of ground state particles.Comment: 11 pages, 12 figure

Delta G from high pT events at SMC and high pT analysis at COMPASS

Measurements of the longitudinal spin cross section asymmetry for deep inelastic muon-nucleon interactions with two high transverse momentum hadrons ($p_T >$ 0.7 GeV) in the final state are presented for SMC data for polarized proton and deuteron and for data on polarized deuteron from COMPASS taken in 2002 and 2003. The muon asymmetries determined with a cut on $Q^2>$ 1 GeV$^2$ in SMC are: $A_p = 0.03 \pm 0.057\pm 0.01$ and $A_d = 0.070 \pm 0.076 \pm 0.010$, respectively. From these values a gluon polarization $\Delta G /G = -0.20\pm 0.28\pm 0.10$ was obtained at an average fraction of nucleon momentum carried by gluons $\eta = 0.07$. The measured asymmetry (with cut on $Q^2>$ 1 GeV$^2$) in COMPASS is $(A_d/D) = -0.015 \pm 0.08 \pm 0.013$ where D is depolarization factor and the gluon polarization $\Delta G /G = 0.06\pm 0.31\pmComment: 4 pages, 3 figures, Talk given at 10-th International Conference Baryons04, October 25-29, 2004, Ecole Polytechnique, Palaiseau, Franc

Evidence for Quark-Hadron Duality in the Proton Spin Asymmetry A_1

Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry A_1. Longitudinally polarized positrons were scattered off a longitudinally polarized hydrogen target for values of Q^2 between 1.2 and 12  GeV^2 and values of W^2 between 1 and 4  GeV^2. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable x. This finding implies that the description of A_1 in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of Q^2 above 1.6  GeV^2