Twist-3 fragmentation functions in a spectator model with gluon rescattering

We study the twist-3 fragmentation functions $H$ and $\tilde{H}$, by applying a spectator model. In the calculation we consider the effect of the gluon rescattering at one loop level. We find that in this case the hard-vertex diagram, which gives zero contribution to the Collins function, does contribute to the fragmentation function $H$. The calculation shows that the twist-3 T-odd fragmentation functions are free of light-cone divergences. The parameters of the model are fitted from the known parametrization of the unpolarized fragmentation $D_1$ and the Collins function $H_1^\perp$. We find our result for the favored fragmentation function is consistent with the recent extraction on $H$ and $\tilde{H}$ from pp data. We also check numerically the equation of motion relation for $H$, $\tilde{H}$ and find that relation holds fairly well in the spectator model.Comment: typo corrected, version published in PL

Orbital structure of quarks inside the nucleon in the light-cone diquark model

We study the orbital angular momentum structure of the quarks inside the proton. By employing the light-cone diquark model and the overlap representation formalism, we calculate the chiral-even generalized parton distribution functions (GPDs) $H_q(x,\xi,\Delta^2)$, $\widetilde{H}_q(x,\xi,\Delta^2)$ and $E_q(x,\xi,\Delta^2)$ at zero skewedness for $q=u$ and $d$ quarks. In our model $E_u$ and $E_d$ have opposite sign with similar size. Those GPDs are applied to calculate the orbital angular momentum (OAM) distributions, showing that $L_u(x)$ is positive, while $L_d(x)$ is consistent with zero compared with $L_u(x)$. We introduce the impact parameter dependence of the quark OAM distribution. It describes the position space distribution of the quark orbital angular momentum at given $x$. We found that the impact parameter dependence of the quark OAM distribution is axially symmetric in the light-cone diquark model.Comment: 15 pages, 6 figure

π−N\pi-N Drell-Yan process in TMD factorization

This article presents the review of the current understanding on the pion-nucleon Drell-Yan process from the point of view of the TMD factorization. Using the evolution formalism for the unpolarized and polarized TMD distributions developed recently, we provide the theoretical expression of the relevant physical observables, namely, the unpolarized cross section, the Sivers asymmetry, and the $\cos2\phi$ asymmetry contributed by the double Boer-Mulders effects. The corresponding phenomenology, particularly at the kinematical configuration of the COMPASS $\pi N$ Drell-Yan facility, is displayed numerically.Comment: Version published in Advances in High Energy Physic

On the beam spin asymmetries of electroproduction of charged hadrons off the nucleon targets

We study the beam single-spin asymmetries $A_{LU}^{\sin\phi_h}$ for charged hadrons produced in semi-inclusive deep inelastic scattering process, by considering the $e H_1^\perp$ term and the $g^\perp D_1$ term simultaneously. Besides the asymmetries for charged pions, for the first time we present the analysis on the asymmetries in the production of charged kaons, protons and antiprotons by longitudinally polarized leptons scattered off unpolarized proton and deuteron targets. In our calculation we use two sets of transverse momentum dependent distributions $g^\perp(x,\bm k_T^2)$ and $e(x,\bm k_T^2)$ calculated from two different spectator models, and compare the numerical results with the preliminary data recently obtained by the HERMES Collaboration. We also predict the beam spin asymmetries for $\pi^\pm$, $K^\pm$, $p/\bar{p}$ electroproduction in semi-inclusive deep-inelastic scattering of 12 GeV polarized electrons from unpolarized proton and deuteron targets.Comment: 9 pages, 6 figures, version accepted by EPJ