Session FL: Hadrons: Nucleon Structure Functions

$\mathrm F_{2}^{P}$ and $\mathrm F_{2}^{d}$ extractions at large Bjorken X from $\mathrm h(e,e^{\prime})$ and $\mathrm d(e,e^{\prime})$ cross sections measured during E12-10-002 in Hall C at Jefferson Lab

Extractions of the $\mathrm F_{2}$ structure functions from inclusive $\mathrm h(e,e^{\prime})$ and $\mathrm d(e,e^{\prime})$ reactions are important for the study of nucleon structure. Such extractions help with constraining the PDF (specially at large Bjorken X), facilitate the studies of Quark Hadron Duality and are important for non-singlet moments calculation as a test of LQCD.\par Experiment E12-10-002 ran in Hall C at JLab in spring 2018 with a focus on measuring the precession cross sections on h and d for $\mathrm F_{2}$ structure functions extraction. Our measurements cover a large kinematic range in X from 0.2 to 1.0, and in $\mathrm Q^{2}$ from 4 to 16 $\mathrm GeV^{2}$.\par I will show the preliminary results of $\mathrm h(e,e^{\prime})$, $\mathrm d(e,e^{\prime})$ cross sections, d/h cross section ratios and $\mathrm F_{2}$ structure functions. I will also discuss the comparison between our data and models such as Christy$'$s f1f220 , CTEQ-JLAB (CJ) and Kulagin (DIS and hybrid) .   

Probing Charge Symmetry Violation in Quark Distributions using SIDIS

Charge symmetry has been universally assumed to be valid in all global fits of data to extract parton distribution functions. At the quark level, the violation of this symmetry arises due to the small mass difference between the up and the down quarks as well as the electromagnetic interaction between the quarks. Although the charge symmetry violation (CSV) is expected to be very small, the precision of the existing data can only constrain it to be $<$ $\pm$ 10 \%. Jefferson Lab Hall-C experiment E12-09-002 was the first experiment that aimed to place the constraints on the degree of CSV in the valence quark distributions in the nucleon via semi-inclusive deep inelastic scattering (SIDIS). In this experiment, a 10.6 GeV electron beam was incident on a liquid deuterium target with the scattered electrons and charged pions detected in coincidence in the HMS and SHMS spectrometers respectively. We measure the ratios of charged pion cross-sections with high precision to extract and place limits on the charge symmetry violating parton distribution functions. Some preliminary results and the current progress in data analysis will be discussed in this talk.   

Precision Measurement of the Neutron Asymmetry $A_1^n$ at Large Bjorken $x$ at 12 GeV JLab

The virtual photon asymmetry $A_1$ is one of the fundamental quantities that provide information on the spin structure of the nucleon. The value of $A_1$ at high $x_{Bj}$ is of particular interest because valence quark dominate in this region, which makes it a relatively clean region to study the nucleon spin structure. There are several theoretical calculations that apply to the high $x$ valence quark region, and here we will focus on the neutron $A_1^n$. With the 12 GeV upgrade of JLab, a new experiment on $A_1^n$ is being carried out using a 10.4 GeV beam, a polarized $^3He$ target, and the HMS and the Super-HMS (spectrometers) in Hall C. This measurement will reach a deeper valence quark region: $x\sim 0.75$. And once combined with expected data from the upgraded CLAS12 experiment on the proton $A_1^p$, we will finally be able to reveal whether $\Delta d/d$ turns positive (as in pQCD) or remain negative at high $x$ (as in RCQM). We will present the physics of $A_1^n$ and present preliminary analysis results of the experiment. Performance of an upgraded polarized $^3He$ target will be presented.   

Probing Nucleon Spin Structure with Deep Inelastic Scattering: Neutron g$_2$ and d$_2$

The experiment E12-06-121 at Jefferson Lab aims to do a precision measurement of the neutron spin structure function g$_2$ using the deep inelastic scattering of electrons over the kinematic range 0.20 $<$ x$_{Bj} <$ 0.95 and 2.5 $<$ Q$^{2} <$ 6.0 (GeV/c)$^2$. The large kinematic coverage will allow for the precision determination of d$_2$, the third moment of the linear combination of the spin structure functions g$_1$ and g$_2$. As one of the cleanest higher twist observables, g$_2$ contains information on quark-gluon correlations and d$_2$ is connected to the ``color polarizability" of the nucleon. The experiment will be performed in Hall C using a longitudinally polarized about 11 GeV electron beam and polarized helium-3 target. The combination of Super High Momentum Spectrometer (SHMS) and High Momentum Spectrometer (HMS) will allow us to run the experiment for four truly constant Q$^2$ values over a wide range of x$_{Bj}$ for the first time. Physics will be explored to test several existing theoretical predictions including Lattice QCD. An overview (the present status) of the experiment will be presented.   

Simultaneous Extraction of Spin-Depedent and Spin-Averaged PDFs at high x

We present a new global QCD analysis of inclusive unpolarized and polarized DIS data, using a Monte Carlo approach to simultaneously extract both the spin-averaged and spin-dependent PDFs. We focus on the high-$x$, low-$W$ region, where effects from power corrections, such as target mass corrections (TMCs) and higher twists, are particularly important. We quantify the effects on the extracted PDFs from various theoretical treatments of the power corrections and cuts on the experimental kinematics.   

SIDIS Single Pion Multiplicity with CLAS12

In the current fragmentation region, the cross section of electroproduced hadrons in Semi-Inclusive Deep Inelastic Scattering (SIDIS) can be expressed as convolution of two universal functions: the partonic distribution functions and the fragmentation functions. The former describing properties of the parton within the nucleon, the latter describing its hadronization process. When the SIDIS cross section is normalized to the deep inelastic scattering cross section - which can be parametrized only in terms of partonic distribution functions - one refers to this observable as multiplicity. In this talk, the preliminary multiplicities of electroproduced pions in SIDIS on an unpolarized hydrogen target are shown by using the JLab CLAS12 data. The high luminosity achieved at JLab and the wide kinematic range covered by the CLAS12 spectrometer have allowed for the extraction of this observable in a multidimensional fashion.   

Measurement of p+d/p+p J/$\psi$ cross section ratio with 120 GeV proton beam in the SeaQuest experiment

The SeaQuest experiment at Fermilab was designed to measure dimuons produced in the interaction of 120 GeV proton beam with liquid hydrogen and liquid deuterium targets. First result on the measurement of sea-quark flavor asymmetry from the p+d/p+p Drell-Yan cross section ratio is expected be reported soon. The SeaQuest experiment also provides a measurement of the p+d/p+p J/$\psi$ cross section ratio, which offer an independent means to examine the sea-quark asymmetry in proton. The interest for measuring the p+d/p+p J/$\psi$ cross section ratio will be discussed. Current status of the analysis will also be presented in this talk.   

Accessing e(x) through di-hadron correlations at CLAS12

Correlations between the azimuthal angles of the hadron pairs produced in semi-inclusive deep-inelastic scattering provide valuable probes of nucleon structure. Several parton distribution functions (PDFs) such as the higher-twist collinear PDF e(x) can be extracted from this information. The PDF e(x) encapsulates knowledge of the interaction between gluons and the struck quark and is sensitive to the pion-nucleon sigma term. The additional degree of freedom present in the two hadron final state allows for additional studies of correlations in the hadronization process, which can provide easier access to e(x) and other observables than in single hadron production. We present preliminary results from charged pion beam-spin asymmetries from data taken in 2018 with the CLAS12 detector at Jefferson Lab. The large kinematic acceptance and sample size allow for a rich multidimensional analysis and a clear signal sensitive to e(x) is observed.