8 research outputs found
Quark Wigner Distributions and Orbital Angular Momentum
We study the Wigner functions of the nucleon which provide multidimensional
images of the quark distributions in phase space. These functions can be
obtained through a Fourier transform in the transverse space of the generalized
transverse-momentum dependent parton distributions. They depend on both the
transverse position and the three-momentum of the quark relative to the
nucleon, and therefore combine in a single picture all the information
contained in the generalized parton distributions and the transverse-momentum
dependent parton distributions. We focus the discussion on the distributions of
unpolarized/longitudinally polarized quark in an unpolarized/longitudinally
polarized nucleon. In this way, we can study the role of the orbital angular
momentum of the quark in shaping the nucleon and its correlations with the
quark and nucleon polarizations. The quark orbital angular momentum is also
calculated from its phase-space average weighted with the Wigner distribution
of unpolarized quarks in a longitudinally polarized nucleon. The corresponding
results obtained within different light-cone quark models are compared with
alternative definitions of the quark orbital angular momentum, as given in
terms of generalized parton distributions and transverse-momentum dependent
parton distributions.Comment: 29 pages, 10 figures, 3 table
The Parton Orbital Angular Momentum: Status and Prospects
Theoretical progress on the formulation and classification of the quark and
gluon orbital angular momenta (OAM) is reviewed. Their relation to parton
distributions and open questions and puzzles are discussed. We give a status
report on the lattice calculation of the parton kinetic and canonical OAM and
point out several strategies to calculate the quark and gluon canonical OAM on
the lattice.Comment: 16 pages, contribution to the EPJA speical issue on "3D Structure of
the Nucleon
Hadron tomography through Wigner distributions
We study the Wigner functions of the nucleon which provide multidimensional
images of the quark distributions in phase space and combine in a single
picture all the information contained in the generalized parton distributions
(GPDs) and the transverse-momentum dependent parton distributions (TMDs). In
particular, we present results for the distribution of unpolarized quarks in a
longitudinally polarized nucleon obtained in a light-cone constituent quark
model. Treating the Wigner distribution as it was a classical distribution, we
obtain the quark orbital angular momentum and compare it with alternative
definitions given in terms of the GPDs and the TMDs.Comment: 6 pages, 1 figure, 1 table, Prepared for the Third International
Workshop on Transverse Polarization Phenomena in Hard Scattering
(Transversity2011), Veli Lo\v{s}inj, Croatia, 29 Aug - 2 Sep 201
The Gluon Sivers Distribution:Status and Future Prospects
We review what is currently known about the gluon Sivers distribution and what are the opportunities to learn more about it. Because single transverse spin asymmetries in p up arrow p -> pi X provide only indirect information about the gluon Sivers function through the relation with the quark-gluon and tri-gluon Qiu-Sterman functions, current data from hadronic collisions at RHIC have not yet been translated into a solid constraint on the gluon Sivers function. SIDIS data, including the COMPASS deuteron data, allow for a gluon Sivers contribution of natural size expected from large N-c arguments, which is O(1/N-c) times the nonsinglet quark Sivers contribution. Several very promising processes to measure the gluon Sivers effect directly have been suggested, which besides RHIC investigations, would strongly favor experiments at AFTER@LHC and a possible future Electron-Ion Collider. Due to the inherent process dependence of TMDs, the gluon Sivers TMD probed in the various processes are different linear combinations of two universal gluon Sivers functions that have different behavior under charge conjugation and that therefore satisfy different theoretical constraints. For this reason both hadronic and DIS type of collisions are essential in the study of the role of gluons in transversely polarized protons.</p
The QCD energy-momentum tensor for massive hadrons of arbitrary spin
International audienceWe present the parametrisation of the energy-momentum tensor (EMT) for massive hadrons of any spin, writing explicitly the expansion in terms of gravitational form factors (GFFs). Such a complete and general parametrisation allows one to derive universal properties that are valid for all hadrons independently of their spin
IUPAP Report 41 Introduction
IUPAP Report 41 is a document that gives summary information about the major nuclear physics facilities around the world. It is updated approximately every five years by Working Group 9 of the International Union of Pure and Applied Physics. The introduction to the report gives an overview of the field of nuclear physics and outlines the major questions facing the field. This most recent version of Report 41 has been updated to reflect the state of the field in 2018. The full report can be found at http://www.triumf.info/hosted/iupap/icnp/report41.htm