Session KH: Nucleon Structure I

Nucleon structure functions at large Bjorken x from 12 GeV commissioning experiment E12-10-002 in Hall C

Extractions of F$_{2}$ structure function from inclusive inelastic electron-proton scattering cross sections is important for the study of nucleon structure. Most existing data have large statistical uncertainties in the region of large Bjorken x. After the successful 12 GeV upgrade of Jefferson Lab, E12-10-002 is one of the first commissioning experiments ran in Hall C to measure the inclusive inelastic electron-proton scattering cross sections in the Q$^{2}$ region of 4 to 14 GeV$^{2}$. In this talk an overview of experiment E12-10-002 and first results will be presented.   

Preliminary cross section and F$_2$ structure function results from E12-10-002 in 12 GeV era at Jefferson Lab

Measurements of H(e,e') and D(e,e') cross sections were done at Jefferson Lab in experimental Hall C in Spring 2018. As part of the 12 GeV early running, we took data to explore a wide range in Bjorken x and to reach a four-momentum transfer Q$^2$ of up to 17 GeV$^2$. In this talk, I will show the preliminary cross section and F$_2$ structure function results of our analysis and I will discuss the upcoming physics output.   

Studies on Nuclear dependence of Anti-Quarks in Nuclei at the SeaQuest experiment

The Fermilab E906/SeaQuest is an experiment aimed at studying the anti-quark distributions in nucleons and nuclei. The experiment uses a 120 GeV proton beam extracted from the Main Injector at Fermilab to collide with liquid deuterium, carbon, iron and tungsten targets to study the nuclear dependence of anti-quarks in nuclei. The experiment takes advantage of the Drell-Yan process and the acceptance is tuned to probe specifically the anti-quark structure in nucleons and nuclei. In the Drell-Yan process, a quark from one hadron annihilates with an anti-quark from another hadron, producing a virtual photon which eventually decays into a dileptons. The ratio of cross sections of these three targets relative to deuterium are studied to extract the relevant nuclear dependence and the physics implications. Recent progress on the nuclear dependence analysis at SeaQuest will be reported in this talk.   

The SpinQuest Polarized Drell-Yan Experiment at Fermilab

The E1039/SpinQuest experiment at Fermilab aims to measure azimuthal asymmetries in the Drell-Yan production of dimuon pairs from 120 GeV/c unpolarized protons scattering off polarized nucleons to extract the Sivers functions for $\bar{u}$ and $\bar{d}$ quarks at 0.1$<$$x$$<$0.5. Measuring a non-zero Sivers asymmetry would be a significant discovery and present strong evidence for non-zero quark orbital angular momentum of sea quarks. First data taking is scheduled for fall 2019. In this talk we will present an experimental overview and current plans for the SpinQuest experiment.   

Constraining the Sea Quark Distributions Through $W$ and $Z$ Cross Sections and Cross Section Ratios Measurements at STAR

Over the past several years, parton distribution functions (PDFs) have become more precise. However there are still kinematic regions where more data are needed to help constrain global PDF extractions, such as the the ratio of the sea quark distributions $\bar{d}$/$\bar{u}$ near the valence region. Current measurements appear to suggest different high-$x$ behaviors of this ratio. The STAR experiment at RHIC is well equipped to measure the leptonic decays for $W$ and $Z$ bosons in proton+proton collisions at $\sqrt{s}$ = 500/510 GeV. These cross sections and their ratios are sensitive to quark and anti-quark distributions. In particular the $W^+/W^-$ cross section ratio is sensitive to the $\bar{d}/\bar{u}$ ratio. RHIC runs from 2011 through 2013 have collected about 350 pb$^{-1}$ of integrated luminosity. This talk will present preliminary results of the 2011-2013 $W^+/W^-$ and $W/Z$ cross section ratios, as well as $W$ and $Z$ differential and total cross sections.   

Constraining the glue in the pion through Drell-Yan lepton pair production

Recently, a new global Monte Carlo analysis of parton distribution functions (PDFs) of the pion determined its valence quark distribution using Drell-Yan data from Fermilab and its sea quark and gluon PDFs from leading neutron electroproduction data from HERA [1]. While that analysis provided greater constraints at small parton momentum fractions $x$, the pion's gluon PDF remains poorly known at large values of $x$. In the present study, we explore the extent to which transverse momentum ($p_T$)-dependent Drell-Yan cross section data can provide for greater sensitivity to the pion's gluon PDF at large $x$. We present preliminary results of a combined QCD analysis of all available $p_T$-integrated and $p_T$-dependent pion data, which will provide the most complete imaging of the PDFs in the pion to date across all momentum fractions. [1] P. Barry et al., Phys. Rev. Lett. 121, 152001 (2018)   

Simultaneous Monte Carlo analysis of parton distributions: a new paradigm in global QCD studies

We report the results of the first simultaneous extraction of unpolarized and polarized parton distributions and parton-to-hadron fragmentation functions from a Monte Carlo analysis of global high energy lepton and hadron scattering data. We use data resampling techniques to thoroughly explore the Bayesian posterior distribution of the extracted functions, and use $k$-means clustering on the parameter samples to identify the configurations that give the best description across all reactions. Inclusion of semi-inclusive deep-inelastic scattering data reveals a strong suppression of the strange quark distribution in the proton, in contrast with recent results from $W^\pm$ and $Z$ production at the LHC. The analysis is the first to include jet production data in both unpolarized and polarized proton-proton collisions, which provides the best constraints to date on the momentum and spin carried by gluons in the proton.