Precision Measurement of the Neutron Asymmetry An 1 at Large Bjorken x at 12GeV Jefferson Lab

Thesis/Dissertation · Wed Nov 01 04:00:00 EDT 2023

OSTI ID:2326020

Chen, Mingyu ^[1]

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1. Univ. of Virginia, Charlottesville, VA (United States)

The virtual photon asymmetry A1 is one of the fundamental quantities that provide information on the spin structure of the nucleon. The value of A1 at high xBj is of particular interest because valence quarks dominate in this region, which makes it a relatively clean region to study the nucleon structure. Several theoretical calculations, including naive SU(6) quark model, relativistic constituent quark model (RCQM), perturbative QCD (pQCD), predict the behavior for A1 and the quark polarization in the high xBj valence quark region. The An 1 experiment during the 6 GeV JLab era showed that An 1 turns positive at x ? 0.5, while up to the highest measured x value of 0.61 the down quark polarization ?d/d remains negative, in contrast to the pQCD prediction. Subsequent theoretical studies following the 6 GeV results claimed that quark orbital angular momentum could delay the upward turn of ?d/d to higher xBj or the non-perturbative nature of the strong interaction could keep it negative all the way to xBj = 1 as predicted in a Schwinger-Dyson approach with di-quark model assumptions. With the 12 GeV upgrade of JLab, a new experiment on An1 (E12-06-110)1 was 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 reached a deeper valence quark region, reaching up to x ? 0.75. This thesis reports on the 3He asymmetries A?, A?, A3He 1 , and A3He 2 without radiative corrections.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 2326020
• Report Number(s): JLAB-PHY-23-4012; DOE/OR/23177-7428
• Country of Publication: United States
• Language: English