181 research outputs found

### 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

### $\pi-N$ 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

- …