Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session DC: 1D Parton Structure of Hadrons I |
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Chair: Amilkar Quintero, Temple University Room: Studio 2 |
Tuesday, October 12, 2021 9:30AM - 9:42AM |
DC.00001: Measurements of the Inclusive Electron Scattering off Protons with CLAS12 Valerii S Klimenko, Nikolay Markov Electron scattering data off protons from the CLAS12 detector in Hall B at Jefferson Laboratory have become available and cover a wide kinematic range in W up to 4 GeV and Q2 up to 10 GeV2, offering new opportunities to explore inclusive, semi-inclusive, and fully exclusive reactions. A study that aims to extract the inclusive electroproduction cross sections from the CLAS12 data collected at a beam energy of 10.6 GeV from an unpolarized liquid-hydrogen target is now in progress and preliminary results will be presented. Because of the large acceptance of CLAS12, these data offer a unique opportunity to measure inclusive cross sections at W from the meson electroproduction threshold to W from 2.0 GeV to 3.0 GeV within any given Q2-bin. This unique W- coverage at fixed Q2-values is of particular importance for the extension of our knowledge on the nucleon parton distribution function from the data on F2 structure function in the resonance region by employing the existing CLAS results on the γpN* electroexcitation amplitudes. These studies also offer valuable input for the exploration of quark-hadron duality. |
Tuesday, October 12, 2021 9:42AM - 9:54AM |
DC.00002: Measurements of $W$ and $Z/\gamma^*$ cross sections and their ratios in $pp$ collisions at STAR Jae D Nam, Matthew R Posik While the unpolarized valence quark ($d$ and $u$) distributions are well determined from DIS experiments, the sea quark distributions, $\bar{d}$ and $\bar{u}$, are much less constrained, in particular, near the valence region. |
Tuesday, October 12, 2021 9:54AM - 10:06AM |
DC.00003: Extraction of Spin-Averaged Light Quark Sea Asymmetry using SeaQuest Data Christopher Cocuzza, Andreas Metz, Jacob Ethier, Wally Melnitchouk, Nobuo Sato We present a new global QCD analysis of inclusive unpolarized data, using a Monte Carlo approach to extract the spin-averaged PDFs. We focus on the light quark sea asymmetry and include new Drell-Yan data from the SeaQuest experiment at Fermilab and $W$-lepton production data from the STAR collaboration at RHIC. We find that the SeaQuest experiment provides strong constraints on the asymmetry, and confirms that it must remain positive up to parton momentum fractions of $x=0.4$, as predicted by models in which the asymmetry arises from chiral symmetry breaking in QCD. |
Tuesday, October 12, 2021 10:06AM - 10:18AM |
DC.00004: Helicity Evolution at Small x: the Single-Logarithmic Contribution Yossathorn Tawabutr, Yuri V Kovchegov, Andrey Tarasov We calculate single-logarithmic corrections to the small-x flavor singlet helicity evolution equations derived recently in the double-logarithmic approximation. The new single-logarithmic part of the evolution kernel sums up powers of αs ln(1/x), which are an important correction to the dominant powers of αs ln2(1/x) summed up by the double-logarithmic kernel derived previously at small values of Bjorken x and with αs the strong coupling constant. The single-logarithmic terms arise separately from either the longitudinal or transverse momentum integrals. Consequently, the evolution equations we derive simultaneously include the small-x evolution kernel and the leading-order polarized DGLAP splitting functions. We further enhance the equations by calculating the running coupling corrections to the kernel. |
Tuesday, October 12, 2021 10:18AM - 10:30AM |
DC.00005: First analysis of world polarized SIDIS data with small-$x$ helicity evolution Daniel M Adamiak, Yuri V Kovchegov, Daniel Pitonyak, Matthew D Sievert, Nobuo Sato, Wally Melnitchouk We use small-$x$ helicity evolution equations to analyze the world polarized DIS and Semi-inclusive DIS (SIDIS) data. After successfully describing the $g_1$ structure function extracted from polarized DIS, we extend this analysis to the small-$x$ $g^h_1$ structure function measured in polarized SIDIS. The fit is performed through a Monte-Carlo analysis within the JAM global framework. Combining the DIS and SIDIS data we are able to extract the individual helicity PDFs for both the light quarks and light anti-quarks. The advantage of our approach is that our evolution predicts the small-$x$ behavior of these helicity distributions, allowing for a precise extrapolation of our helicity PDFs to smaller values of $x$, in the region that cannot be accessed experimentally. This brings us one step closer to resolving the proton spin problem. |
Tuesday, October 12, 2021 10:30AM - 10:42AM |
DC.00006: Calculation of the d/u ratio at large x in the residual mean field model Christopher A Leon, Misak M Sargsian We developed a new model to describe the non-singlet patron distribution functions (PDFs) for valence quarks inside the nucleon. In the model three relativistic, massless valence quarks reside in the strong residual field of the nucleon. The calculations are performed using the light front diagrammatic framework. We calculated the down and up valence PDFs covering a range of 0.1 < x < 1. The parameters of the model were fitted to match the PDF peak height and position at x ≈ 0.2. With these parameters we get dV(x)/uV (x). The result of dV(x)/uV (x)| x→1 ≈ 0.21 is in good agreement with recent data and analyses. We discuss calculations of other observables. |
Tuesday, October 12, 2021 10:42AM - 10:54AM |
DC.00007: Inverse Mappers for QCD global analysis Manal Almaeen, Nobuo Sato, Wally Melnitchouk, Yaohang Li We present a new Machine Learning technique based on Variational Autoencoders in the context of deep learning to construct an effective “inverse function” that maps experimental data into quantum correlation functions (QCFs) such as parton distribution functions in the nucleon. As such it provides a powerful complementary tool for QCD global analysis where the Bayesian inference associate with the inverse problem of QCFs can be implemented efficiently allowing the possibility to explore systematically different choices for the likelihood functions, Bayesian priors and have the possibility to understand in great detail how each data point or sets of data points influence the uncertainty quantification for the QCFs. |
Tuesday, October 12, 2021 10:54AM - 11:06AM |
DC.00008: Measuring the Neutron Spin Asymmetry A1n in the Valence Quark Region in Hall C at Jefferson Lab Melanie Rehfuss, Zein-Eddine Meziani Due to the non-perturbative nature of QCD, making absolute predictions of nucleon spin structure is generally difficult. While successful lattice QCD calculations of spin and orbital angular momentum (OAM) of the quarks and gluons, integrated over their longitudinal momentum fraction (xbj), exist, there remains much to learn about their xbj-dependence. With the breakthrough of the quasi-PDFs formalism, confronting ab-initio calculations of unintegrated spin observables including OAM will be possible. The neutron spin asymmetry A1n at high xbj is a key observable for probing nucleon spin structure since in the valence domain (xbj > 0.5) sea effects are expected to be negligible, where the total nucleon spin is considered to be carried by the valence quarks, and can enable us to study the role of quark OAM and other non-perturbative effects of the strong force. A1n was measured in the deep inelastic scattering region of 0.30 < x < 0.75 and 3 < Q2 < 10 (GeV/c)2 in Hall C at Jefferson Lab using a 10.4 GeV longitudinally polarized electron beam, upgraded polarized 3He target, and the High Momentum Spectrometer (HMS) and Super High Momentum Spectrometer (SHMS). The wide Q2 range will explore possible Q2 dependence on A1n, provide the first precision data in the valence quark region above xbj = 0.61, and therefore test various predictions and ultimately ab-initio lattice QCD calculations. |
Tuesday, October 12, 2021 11:06AM - 11:18AM |
DC.00009: Precision Measurement of Neutron g2 and d2 at Jefferson Lab Junhao Chen, Todd D Averett Serving as a precision measurement of the neutron spin structure function g2 and first time evaluation of the d2 at constant Q2 for Q2 > 1 GeV2/c2, the expeiment E12-06-121 was successfully completed in Hallc C of Jefferson Lab. While g2 contains information of quark-gluon correlations, d2, which is a linear combination of g1 and g2, is related to "color polarizabilities" and color Lorentz force acting on stuck quark. This experiement utilized the longitudinally polarized 10.4 GeV electron beam and a polarized helium-3 target which can be polarized both longitudinally and transversely. Aslo the large acceptance of the Super High Momentum Spectrometer (SHMS) combined with High Momentum Spectrometer (HMS) allows the measurment over nearly constan Q2 in a very broad xBj region. This work will present an overview of the experiment and preliminary results from data analysis. |
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