THE QCD PARTON MODEL: A USEFUL APPROXIMATION

Approximate relations among transverse momentum dependent quark distribution functions are established in the framework of the QCD parton model. The validity of such results survives QCD evolution effects, owing to the Politzer theorem on equations of motion. Furthermore the model fixes an energy scale, involved in the parametrization of the correlator, which determines the Q2 dependence of the azimuthal asymmetries in inclusive reactions. Some of the present data — in particular the sin 2ϕ single spin asymmetry in semi-inclusive deep inelastic scattering (SIDIS) and the cos ϕ asymmetry in unpolarized SIDIS — support model predictions. Further measurements of SIDIS and Drell–Yan asymmetries are suggested, in particular the SIDIS double spin asymmetry, which allows to determine approximately the proton transversity.

Download Full-text

Asymmetry Effects in Polarized Hadron Scattering

International Journal of Modern Physics A ◽

10.1142/s0217751x97003054 ◽

1997 ◽

Vol 12 (32) ◽

pp. 5827-5846

Author(s):

Yaw-Hwang Chen ◽

Su-Long Nyeo ◽

Chung-Yi Wu

Keyword(s):

Cross Sections ◽

Differential Cross ◽

Helicity Amplitude ◽

Spin Asymmetry ◽

Distribution Functions ◽

Differential Cross Sections ◽

Parton Distribution Functions ◽

Double Spin Asymmetry ◽

Single Spin ◽

Double Spin

We calculate the single-spin and double-spin asymmetry differential cross sections for the polarized hadron scattering PP → l+ l- + jet up to O(αs) by the helicity amplitude method. Numerical results of the differential cross sections, which can be used to probe the spin contents of the proton, are obtained from several sets of polarized parton distribution functions.

Download Full-text

The role of transverse momentum on the nuclear valence and sea quark distribution functions

The European Physical Journal C ◽

10.1140/epjc/s10052-020-7720-5 ◽

2020 ◽

Vol 80 (2) ◽

Author(s):

H. Nematollahi

Keyword(s):

Transverse Momentum ◽

Quark Distribution ◽

Parton Model ◽

Distribution Functions ◽

Momentum Dependence ◽

Free Nucleon ◽

Parton Distribution Functions ◽

Transverse Momentum Dependent ◽

Nuclear Modifications

Abstract We investigate the transverse momentum dependence of valence and sea quark distribution functions of light asymmetric nuclei ($$^{3}He$$3He and $$^{7}Li$$7Li). To this end, we first calculate the valence and sea distributions of these nuclei applying a parametrization method in which the parton distribution functions (PDFs) of nucleus are related to those of free nucleon via a weight function that contains the nuclear modifications. Then we obtain the unpolarized transverse momentum dependent (TMD) PDFs of the nucleus using the covariant parton model (CPM) approach. We also compute the valence and sea quark distributions ratios of $$^{3}He$$3He and $$^{7}Li$$7Li to those of deuteron and present the results with respect to x (Bjorken variable) at fixed values of transverse momentum. It is found that these ratios shift to the larger values of x by increasing the transverse momentum value as expected and they are not transverse momentum dependent in large x region.

Download Full-text

SINGLE/DOUBLE-SPIN ASYMMETRY MEASUREMENTS OF SEMI-INCLUSIVE PION ELECTRO-PRODUCTION ON A TRANSVERSELY POLARIZED 3He TARGET THROUGH DEEP INELASTIC SCATTERING

Modern Physics Letters A ◽

10.1142/s0217732312300212 ◽

2012 ◽

Vol 27 (21) ◽

pp. 1230021

Author(s):

◽

XIN QIAN

Keyword(s):

Inelastic Scattering ◽

Deep Inelastic Scattering ◽

Parton Distribution ◽

Spin Asymmetry ◽

Valence Quark ◽

Distribution Functions ◽

Scattered Electron ◽

Parton Distribution Functions ◽

Transverse Momentum Dependent ◽

Double Spin

Parton distribution functions, which represent the flavor and spin structure of the nucleon, provide invaluable information in illuminating quantum chromodynamics in the confinement region. Among various processes that measure such parton distribution functions, semi-inclusive deep inelastic scattering is regarded as one of the golden channels to access transverse momentum dependent parton distribution functions, which provide a 3D view of the nucleon structure in momentum space. The Jefferson Lab experiment E06-010 focuses on measuring the target single and double spin asymmetries in the [Formula: see text] reaction with a transversely polarized 3 He target in Hall A with a 5.89 GeV electron beam. A leading pion and the scattered electron are detected in coincidence by the left High-Resolution Spectrometer at 16° and the BigBite spectrometer at 30° beam right, respectively. The kinematic coverage concentrates in the valence quark region, x ~ 0.1–0.4, at Q2 ~ 1–3 GeV 2. The Collins and Sivers asymmetries of 3 He and neutron are extracted. In this review, an overview of the experiment and the final results are presented. Furthermore, an upcoming 12-GeV program with a large acceptance solenoidal device and the future possibilities at an electron–ion collider are discussed.

Download Full-text

Transverse-momentum-dependent quark distribution functions of spin-one targets: Formalism and covariant calculations

Physical Review C ◽

10.1103/physrevc.96.045206 ◽

2017 ◽

Vol 96 (4) ◽

Cited By ~ 8

Author(s):

Yu Ninomiya ◽

Wolfgang Bentz ◽

Ian C. Cloët

Keyword(s):

Transverse Momentum ◽

Quark Distribution ◽

Distribution Functions ◽

Transverse Momentum Dependent

Download Full-text

Color Entanglement in Hadronic Processes for Transverse Momentum Dependent Parton Distribution Functions

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194515600228 ◽

2015 ◽

Vol 37 ◽

pp. 1560022

Author(s):

M. G. A. Buffing ◽

P. J. Mulders

Keyword(s):

Transverse Momentum ◽

Parton Distribution ◽

Distribution Functions ◽

Parton Distribution Functions ◽

Initial State ◽

Color Flow ◽

Transverse Momentum Dependent ◽

Gauge Link ◽

Azimuthal Asymmetries ◽

Different Parts

In the description of protons, we go beyond the ordinary collinear parton distribution functions (PDFs), by including transverse momentum dependent PDFs (TMDs). As such, we become sensitive to polarization modes of the partons and protons that one cannot probe without accounting for transverse momenta of partons, in particular when looking at azimuthal asymmetries. Hadronic processes require the inclusion of gluon contributions forming the gauge links, which are path-ordered exponentials tracing the color flow. In processes with two hadrons in the initial state, such as Drell-Yan (DY), the gauge links from different parts of the process get entangled. We show that in color disentangling this gauge link structure, one becomes sensitive to this color flow. After disentanglement, particular combinations of TMDs will require a different numerical color factor than one naively might have expected. Such color factors will even play a role for azimuthal asymmetries in the simplest hadronic processes such as DY.

Download Full-text

Single-spin asymmetry ATsin(2ϕ−ϕS) in π−p Drell-Yan process within TMD factorization

EPJ Web of Conferences ◽

10.1051/epjconf/202225803002 ◽

2022 ◽

Vol 258 ◽

pp. 03002

Author(s):

Hui Li ◽

Xiaoyu Wang ◽

Zhun Lu

Keyword(s):

Spin Asymmetry ◽

Distribution Functions ◽

Single Spin Asymmetry ◽

Parton Distribution Functions ◽

Sudakov Form Factor ◽

Transverse Momentum Dependent ◽

Single Spin ◽

Mulders Function ◽

Light Cone Wave Function ◽

The Asymmetry

We study the single-spin asymmetry ATsin(2ϕ−ϕS) in the pion-induced Drell-Yan process within the transverse momentum dependent factorization (TMD factorization). The asymmetry can be expressed as the convolution of the Boer-Mulders function and the transversity function. We numerically estimate the asymmetry ATsin(2ϕ−ϕS) at the COMPASS kinematics with the model results for the pion meson distributions from the light-cone wave function approach and the available parametrization for the proton distributions. We also include the TMD evolution formalism both proton and pion parton distribution functions by using two different parametrizations on nonperturbative Sudakov form factor. We find that the asymmetry ATsin(2ϕ−ϕS) as functions of xp, xπ, xF and q⊥ is qualitatively consistent with the recent COMPASS measurement.

Download Full-text