Search

In this paper, we study the contribution of color correlations to Double Parton Scattering (DPS). We show that there is a specific class of Feynman diagrams related to so-called 1 → 2 processes when the contribution of these color correlations is not Sudakov suppressed with the transverse scales. The effective absence of Sudakov suppression gives hope that although they are small relative to color singlet correlations, they eventually can be observed. [ABSTRACT FROM AUTHOR]

Abstract: In this review, we present and discuss the most recent results on inclusive and exclusive diffractive processes at HERA and Tevatron colliders. Measurements from fixed target experiments at HERMES and Jefferson laboratory are also reviewed. The complementarity of all these results is analyzed in the context of perturbative QCD and new challenging issues in nucleon tomography are studied. A first understanding of how partons are localized in the nucleon to build orbital momenta can be addressed with these experimental results. Some prospects are outlined for new measurements in fixed target kinematic, at Jefferson laboratory and CERN, at COMPASS, or at the LHC. Of special interest is the exclusive (coherent) production of Higgs boson and heavy objects at the LHC. Based on the present knowledge, some perspectives are presented on this issue. [Copyright &y& Elsevier]

Abstract: We calculate the non-forward quark matrix elements of operators with two covariant derivatives needed for the renormalisation of the second moment of generalised parton distributions in one-loop lattice perturbation theory using Wilson fermions. For some representations of the hypercubic group commonly used in simulations we determine the sets of all possible mixing operators. For those representations the one-loop mixing matrices of renormalisation factors are found. Due to non-vanishing contributions of operators with external ordinary derivatives the number of contributing operators increases compared to forward matrix elements. [Copyright &y& Elsevier]

We report on a measurement of hard exclusive π 0 muoproduction on the proton by COMPASS using 160 GeV/ c polarised μ + and μ − beams of the CERN SPS impinging on a liquid hydrogen target. From the average of the measured μ + and μ − cross sections, the virtual-photon proton cross section is determined as a function of the squared four-momentum transfer between initial and final proton in the range 0.08 (GeV / c) 2 < | t | < 0.64 (GeV/ c) 2. The average kinematics of the measurement are 〈 Q 2 〉 = 2.0 (GeV / c) 2 , 〈 ν 〉 = 12.8 GeV , 〈 x B j 〉 = 0.093 and 〈 − t 〉 = 0.256 (GeV / c) 2. Fitting the azimuthal dependence reveals a combined contribution by transversely and longitudinally polarised photons of (8.2 ± 0.9 stat − 1.2 + 1.2 | sys) nb / (GeV / c) 2 , as well as transverse-transverse and longitudinal-transverse interference contributions of (− 6.1 ± 1.3 stat − 0.7 + 0.7 | sys) nb / (GeV / c) 2 and (1.5 ± 0.5 stat − 0.2 + 0.3 | sys) nb / (GeV / c) 2 , respectively. Our results provide important input for modelling Generalised Parton Distributions. In the context of the phenomenological Goloskokov-Kroll model, the statistically significant transverse-transverse interference contribution constitutes clear experimental evidence for the chiral-odd GPD E ‾ T. [ABSTRACT FROM AUTHOR]