Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session B04: Nucleon Structure at Large xInvited Live Streamed
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Sponsoring Units: DNP GHP Chair: Shujie Li, Lawrence Berkeley National Laboratory Room: Salon 2 |
Saturday, April 9, 2022 10:45AM - 11:21AM |
B04.00001: Overview of quark distributions at Large x Invited Speaker: Aurore Courtoy Hadron structure in the large-x regime offers a window on the nonperturbative nature of parton distribution functions (PDFs). It is in the valence region where low-energy models are meaningful, and at x going to 1 where the first principles of QCD guide the shape of the PDFs. It is then tantalizing to explore the large-x region to bridge the perturbative and nonperturbative pictures of QCD. In this talk, we discuss phenomenological efforts towards describing the hadron structure at large x using global QCD analyses, from low to high energy. We review experimental as well as theoretical developments. We expand on the role of first-principle constraints on PDFs in general. |
Saturday, April 9, 2022 11:21AM - 11:57AM |
B04.00002: New Results on Nucleon Structure in the Valence Quark Region at Large Bjorken-x Invited Speaker: Michael E Christy Lepton scattering has provided a powerful tool in both establishing Quantum Chromodynamics as the correct theory for the strong interaction and for unraveling the internal structure of nucleons and nuclei in terms of the fundamental quarks and gluons (partons) constituents. Structure functions extracted from inclusive scattering cross sections and their spin asymmetries provide critical information on this structure and depend on both the 4-momentum transfer and the Bjorken scaling variable, x, representing the longitudinal momentum fraction of the nucleon carried by the struck quark. At large values of x, where the scattering is dominated by a single valence quark, the momentum distributions can be more directly related to the nonperturbative structure of the nucleon. In this talk I will discuss recent developments in understanding nucleon structure at large x, from both polarized and unpolarized scattering, with particular emphasis on the new generation of experiments at Jefferson Lab utilizing the upgraded 12 GeV electron accelerator. |
Saturday, April 9, 2022 11:57AM - 12:33PM |
B04.00003: Polarized Nucleon Structure at Large x Invited Speaker: Xiaochao Zheng The virtual photon asymmetry of the neutron $A_1^n$ is one of the fundamental quantities which provides information about the spin structure of the nucleon. $A_1^n$ at high $x$ is of particular interest because valence quarks dominate in this region, allowing for a cleaner interpretation of experimental results in terms of the nucleon spin structure. The 6 GeV Jefferson Lab (JLab) results on $A_1^n$ showed that the down quark helicity in the proton ($\Delta d/d$) is negative up to $x\approx 0.61$, in contrast with pQCD predictions that $\Delta d/d$ turns positive and approaches 1 at $x\to 1$. In this talk I will report on a recently completed precision $A_1^n$ measurement using the 11 GeV beam and an upgraded polarized $^3$He target at Jefferson Lab, that provided data up to $x=0.75$. |
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