Narrow Results

In this paper, we construct the generalized parton distribution (GPD) in terms of the kinematical variables $x$, $\xi$, $t$, using the double distribution model. By employing these functions, we could extract some quantities which makes it possible to gain a three-dimensional insight into the nucleon structure function at the parton level. The main objective of GPDs is to combine and generalize the concepts of ordinary parton distributions and form factors. They also provide an exclusive framework to describe the nucleons in terms of quarks and gluons. Here, we first calculate, in the Double Distribution model, the GPD based on the usual parton distributions arising from the GRV and CTEQ phenomenological models. Obtaining quarks and gluons angular momenta from the GPD, we would be able to calculate the scattering observables which are related to spin asymmetries of the produced quarkonium. These quantities are represented by $A_N$ and $A_{LS}$. We also calculate the Pauli and Dirac form factors in deeply virtual Compton scattering. Finally, in order to compare our results with the existing experimental data, we use the difference of the polarized cross-section for an initial longitudinal leptonic beam and unpolarized target particles $(\mathrm{\Delta }{\sigma }_{LU})$. In all cases, our obtained results are in good agreement with the available experimental data.

Sivers effect is describing the correlation between the transverse polarization of nucleon and the transverse momentum, $k_{\perp }$, of its unpolarized constituent partons. This effect is an outstanding subject and in this regard, a great deal in recent years has been considered from experimental and phenomenological points of view. It also plays an essential role to extend our understanding from nucleon structure. Semi-inclusive DIS (SIDIS) process provides us an opportunity to access to Sivers function which is dependent on transverse momentum of partons. In this paper, for the first time the covariant parton model is used to deliver us the $k_{\perp }$ and $x$ dependence part of Sivers function. Based on this model, this combinatory dependence is arising out from the HERAPDF parametrization group. In this paper the other required parametrized functions in Sivers function is also changed with respect to Ref. 1. The unknown parameters which exist in Sivers function can be extracted, doing a global fit over the recent available experimental data, including HERMES, COMPASS and JLAB collaborations for the single spin asymmetry (SSA) in ${\pi }^{-}$ and ${\pi }^{+}$ meson production as well as kaon production to constrain the evolved strange quark. This is done, considering advanced mathematical manipulations to overcome the difficulties which exist to compute the required multiple integrals and finally employing the CERN MINIUTE program to do a global fit. Our results for SSA are in good agreement with the available experimental data. For more confirmation a comparison between our results and the ones from Ref. 2 is also done.

We present a recent calculation of single-inclusive high-p_T jet production in pp collisions at RHIC, when the initial protons are unpolarized and also when they are longitudinally polarized. We investigate the effect of the algorithm adopted to define the jets on the numerical results of cross sections and spin asymmetries.

In the two papers published recently,^{1, 2} we apply collinear expansion to both inclusive ($e^{+}{e}^{-}\to h+X$) and semi-inclusive ($e^{+}{e}^{-}\to h+\bar{q}+X$) hadron production in $e^{+}{e}^{-}$ annihilation to derive a formalism suitable for a systematic study of leading as well as higher twist contributions to fragmentation functions at the tree level. We carry out the calculations for hadrons with spin-0, spin-1/2 as well as spin-1. This proceeding is mainly a summary of these two papers.