Abstract
In the spectator models of the nucleon with scalar and axial-vector diquarks, we show that the effect of Pauli coupling in photon-quark vertex to the parton distribution functions (PDFs) of nucleon and azimuthal asymmetry in the unpolarized semi-inclusive deep inelastic scattering (SIDIS). This anomalous coupling gives obvious contribution to unpolarized and polarized PDFs, and also leads to a $\cos 2\phi_h$ azimuthal asymmetry proportional to the squared Pauli form factor, due to the helicity flip of the struck quark. After determining the model parameters by fitting PDFs to the global fits, this new distribution for $\cos 2\phi_h$ asymmetry is given numerically. In the framework of transverse momentum dependence (TMD), we find that it is positive and of a few percent in the kinematical regime of HERMES and COMPASS collaborations, in the same order of magnitude with Cahn effect.
Highlights
The semi-inclusive deep inelastic scattering (SIDIS) plays an essential role in studying the parton distribution functions (PDF) of the nucleon, and its azimuthal asymmetries are important observables related to the transverse spin of quarks inside target hadrons [1]
One of them involves the convolution of the Boer-Mulders function [2], which measures the transverse polarization asymmetry of quarks inside an unpolarized hadron and the spin-dependent Collins fragmentation function (FF) of the produced hadron [3,4]
It does not affect the kinematical relationships of involved momenta, but it would influence the virtualities of internal lines of hard scattering
Summary
The semi-inclusive deep inelastic scattering (SIDIS) plays an essential role in studying the parton distribution functions (PDF) of the nucleon, and its azimuthal asymmetries are important observables related to the transverse spin of quarks inside target hadrons [1]. Dirac vector coupling is widely explored in the quark electromagnetic and chromomagnetic current, but the tensor coupling with respect to the anomalous Pauli form factor is less recognized These Pauli couplings can flip the quark helicity, which is one of the important ingredients to induce single-spin asymmetries (SSA) in SIDIS. Alternative approaches, e.g., instanton background field [25], MIT bag model [26], and single instanton approximation [27], arrive at similar conclusions This remarkable mechanism could be promising for our understanding of the large SSAs observed in high-energy hadronic reactions and in SIDIS [1]. High-energy elastic pp scattering [33], and in the pp → π0X reaction [34] In these analyses it was suggested that this quark-gluon interaction would cause the explicit breakdown of transverse-momentum-dependent (TMD) factorization.
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