Session LL: Mini-Symposium: Nucleon Structure in the Valence Regime II

Recent Progress in Lattice Nucleon Parton Distribution Calculations

The large‐momentum effective theory (LaMET) framework has been widely used to calculate the Bjorken‐$x$ dependence of PDFs in lattice‐QCD hadron-structure calculations. In this talk, I will review the latest progress made in lattice-QCD towards the nucleon parton distribution function both in LaMET and traditional moment methods.   

Comparing Quark Distribution Moments Extracted from Experimental Data to Precision Lattice QCD Calculations

Thanks to advances in Lattice QCD (LQCD), calculations of the moments of quark flavor Parton Distribution Function (PDF) combinations are now available. These precision calculations can be compared to quark distribution moments extracted from experimental data, specifically using the difference between the proton and neutron $F_{2}$ structure function moments. Details of the analysis and the resulting comparison with numerous different LQCD calculations will be presented. This work is supported in part by NSF grant PHY-1812369.   

Short-Range Correlations and the Free-Neutron Valance Structure

The lack of a neutron target has resulted in a decades-long effort to understand the free neutron structure in order to test SU(6) symmetry breaking mechanisms. Approaches to address this open question span a wide range of activities, many focused on extracting~the free neutron structure from proton $+$ deuterium DIS data. Here we present a novel approach to extracting the free neutron structure by utilizing all available structure functions of nuclei (from deuterium to lead), while consistently accounting for partonic medium-modifications in atomic nuclei. Using such a wide span of nuclei provides a large lever arm that allows us to precisely constrain the neutron~structure function, even at high-x. We also discuss extracting the free neutron structure from A$=$3 nuclei, as proposed by the MARATHON collaboration, and the theoretical uncertainties associated with such an extraction.~Finally, we present a complimentary approach to extracting nucleon modification from A$=$2,3 nuclei within a convolution model.   

Systematics of Deuteron Smearing Corrections in Global PDF fits

Use of DIS data on light A=2,3 nucleus targets for up and down quark flavor separation at large x crucially depends on the theoretical treatment of nuclear effects such as binding and Fermi motion, and off-shell deformation of the quark and gluon structure of bound nucleons. The amount and precision of available data from JLab 6 and, increasingly, from the JLab 12 experimental programs require a correspondingly precise treatment of nuclear corrections. In this talk, I will discuss recent work that scrutinizes systematic uncertainties in the so-called nuclear smearing, and its applications to global QCD fits of parton distribution functions at large x values.   

A new comparison of the F2A/F2p and F2A/F2n structure function ratios

Using electron scattering data from SLAC E139 and muon scattering data from NMC in the DIS region, we determine the F2A/F2p and F2A/F2n structure function ratios, spanning 0.3 lt xlt 0.8 and 1 lt Q2 lt 200 GeV/c This region is of particular relevance to studies of the EMC Effect. The structure of the free proton is well known from numerous experiments, but the free neutron structure function has remained difficult to access. Recently, the free neutron structure function has been extracted in a systematic study of the global data within a parton distribution function extraction framework and is available from the CTEQ-Jefferson Lab (CJ) Collaboration. In this talk, we leverage the recent global free neutron extraction to introduce a new method to study the EMC Effect in nuclei by re-examining existing data and by now determining the magnitude of the medium modifications to the free neutron and proton structure functions, independently. We further examine the nuclear effects in deuterium and their contribution to our interpretation of the EMC Effect. This talk will summarize the results of the mentioned ratios for the SLAC E139 nuclei using the F2n global data from the CJ Collaboration.   

Extracting the Neutron Structure Function F2 from DIS Data with the CJ15 Global Fit

The CJ (CTEQ-Jefferson Lab) Collaboration provides a global fit of parton distribution functions (PDFs) with a special emphasis on the large x region. The latest fit (CJ15) implemented deuteron nuclear corrections at the parton level, and included data that were sensitive specifically to the neutron. These nuclear corrections allow for a calculation of the F2 structure functions of the proton, deuteron, and neutron from PDFs. In this work we re-estimated the uncertainties in the DIS F2 data utilized in CJ15, and collected an extended set of existing high-precision, small Q2, large x DIS data from JLab 6 GeV experiments. We employed the CJ15 calculation to remove nuclear effects from deuteron data where the proton was available from the same experiment, and thereby constructed a global data set for the F2 neutron structure function. In this talk, we will present the extracted F2 neutron data sets, as well as applications such as new neutron excess (isoscalar) corrections and a comparison to lattice QCD.   

Measuring the Neutron Spin Asymmetry A$_{\mathrm{1}}^{\mathrm{n}}$ in the Valence Quark Region in Hall C at Jefferson Lab

The ``spin crisis'' ushered in by the measurements on the integral of the proton polarized structure function g$_{\mathrm{1}}^{\mathrm{p}}$ conducted at SLAC and CERN, which revealed that the spin contribution of the valence and sea quarks comprised only a small fraction of the total proton spin, has inspired immense theoretical and experimental activity on nucleon spin structure. The extent to which quark (and gluon) angular momentum plays in forming the nucleon spin is still a mystery. Since QCD has a non-perturbative nature, the valence domain (x$_{\mathrm{bj}}$ \textgreater 0.5) is an ideal region to explore nucleon spin structure because it's considered to be a perturbative region, where the valence quarks dominate, and so is the only region where pQCD and many other models can make absolute predictions for structure function ratios. The neutron spin asymmetry A$_{\mathrm{1}}^{\mathrm{n}}$ was measured in the deep inelastic scattering region of 0.3 \textless x \textless 0.77 and 3 \textless Q$^{\mathrm{2}}$ \textless 10 (GeV/c)$^{\mathrm{2}}$ in Hall C at Jefferson Lab using an 10.4 GeV longitudinally polarized electron beam, upgraded polarized $^{\mathrm{3}}$He target, and the High Momentum Spectrometer (HMS) and Super High Momentum Spectrometer (SHMS). The wide Q$^{\mathrm{2}}$ range will explore possible Q$^{\mathrm{2}}$ dependence on A$_{\mathrm{1}}^{\mathrm{n}}$, provide the first precision data in the valence quark region above x $=$ 0.61, and therefore test various predictions from the relativistic constituent quark model and perturbative QCD.