Conveners
Nucleon Helicity Structure: Helicity I
- Andrey Tarasov (North Carolina State University)
Nucleon Helicity Structure: Helicity III
- Andrey Tarasov (North Carolina State University)
Nucleon Helicity Structure: Helicity IV
- Andrey Tarasov (North Carolina State University)
Nucleon Helicity Structure: Helicity V
- Sebastian Kuhn (Old Dominion University)
Nucleon Helicity Structure: Helicity VI
- Sebastian Kuhn (Old Dominion University)
How do quarks and gluons conspire to provide the total spin of proton is a long-standing puzzle in quantum chromodynamics (QCD). The unique capability of RHIC, that can provide longitudinally polarized $p+p$ collisions at both $\sqrt{s} = 200$ GeV and $\sqrt{s} = 510$ GeV, opened new territory to constrain the helicity structure of the proton with unprecedented depth and precision.
Results...
Run Group C (RGC) is a series of Electron-nucleon scattering experiments sensitive to target- and double-spin observables. It has been recently performed with the CLAS12 spectrometer in Hall B at Jefferson Lab. The experiments scattered highly polarized 11 GeV electrons by longitudinally polarized proton/neutron targets, a first with the newly upgraded CLAS12. In this presentation, we overview...
After decades of study of the nucleon spin structure, the deep-valence quark (high x) region remains difficult to access experimentally. On the other hand, the deep valence quark region is is a clean testing ground of various predictions for the ratio of polarized and unpolarized structure functions, and quark polarization inside the proton. These predictions include relativistic...
Parton distribution functions (PDFs) capture the one-dimensional longitudinal momentum structure of hadrons and relate the properties of hadrons to their constituent quarks and gluons. Helicity PDFs, in particular, encode information directly relevant to the origin of hadron spin. Our knowledge of the PDFs of the nucleon has been significantly improved by the wealth of data from the Large...
I describe recent progress by the HadStruc Collaboration at extracting the helicity distribution from Lattice QCD calculations using the pseudo-PDF framework. I begin by briefly outlining the pseudo-PDF framework, before proceeding to its implementation for our study of the gluon PDF. I describe the variety of methods employed to overcome the poor signal-to-noise ratios inherent in such...
Pseudo-distributions, which regularized co-linear divergences using space-like separations in quark bilinear operators, are accessible from lattice QCD calculations in Euclidean space. In the recent years, parton distribution functions have been computed in lattice QCD using this approach. In this talk I present recent results by the HadStruc collaboration utilizing the pseudo-distribution approach.
Quasi parton distribution functions (QPDFs) are defined in terms of QCD fields at spacelike separations evaluated in matrix elements of hadrons moving with velocity v. These objects can be studied in lattice QCD. In the limit when v approaches the speed of light, QPDFs converge in PDFs. It is insightful to study QPDFs and their convergence in models. In this work, we first study the QPDFs in a...
The SeaQuest experiment at Fermilab is designed to detect the Drell-Yan process in $p+p$ and $p+d$ reactions using the 120 GeV proton beam from the FNAL Main Injector in a fixed-target arrangement. SeaQuest recently observed a large $\bar{d}(x)/\bar{u}(x)$ asymmetry up to Bjorken $x$ as large as 0.45. The mechanism of this asymmetry has been studied via various theoretical models, and it was...
We present an update on the calculation of nucleon quark distribution functions using a confining Nambu-Jona-Lasinio (NJL) model. Originally developed for nucleons, the NJL model is now seen as an effective theory of low-energy QCD that is based on quark degrees of freedom. The nucleon bound state is obtained by solving the Faddeev equation in the quark–diquark approximation, where we include...
We present the latest global QCD analysis results from the Jefferson Lab Angular Momentum (JAM) collaboration on helicity PDFs. We focus on the light quark sea asymmetry, including in the analysis the latest $W$-lepton production data from the STAR collaboration at RHIC, as well as the sign of the gluon's helicity, including the latest jet production data from RHIC. We find a nonzero sea...
Understanding the contribution of gluons to the spin of the proton is crucial for unraveling the proton spin puzzle. This has been one of the primary motivations behind the spin program conducted at the Relativistic Heavy Ion Collider (RHIC). The longitudinal spin structure of the proton is probed by colliding two protons with longitudinal polarization ($\vec{p}+\vec{p}$) and measuring the...
Understanding the origin of the proton spin is one of the most fundamental and challenging questions in QCD. Much progress has been made since the first surprising result by the EMC experiment in the late 1980s. However, the helicity distributions of strange quarks and anti-quarks inside the proton are still not well constrained by the experimental data. Measurement of the longitudinal double...
We construct an exact analytic solution of the revised small-$x$ helicity evolution equations derived previously. The equations we solve are obtained in the large-$N_c$ limit (with $N_c$ the number of quark colors) and are double-logarithmic (summing powers of $\alpha_s \ln^2(1/x)$ with $\alpha_s$ the strong coupling constant and $x$ the Bjorken $x$ variable). Our solution provides small-$x$,...
We revisit the problem of the small Bjorken-$x$ asymptotics of the quark and gluon orbital angular momentum (OAM) distributions in the proton utilizing the revised formalism for small-$x$ helicity evolution derived recently in [1]. We relate the quark and gluon OAM distributions at small $x$ to the polarized dipole amplitudes and their (first) impact-parameter moments. To obtain the...
The sensitivity to the strong coupling $\alpha_S(M^2_Z)$ is investigated using existing Deep Inelastic Scattering data from HERA in combination with projected future measurements from the Electron Ion Collider (EIC) in a next-to-next-to-leading order QCD analysis. A potentially world-leading level of precision is achievable when combining simulated inclusive neutral current EIC data with...
