[PDF] Precision Measurement Of The Neutron Spin Asymmetry Asub 1sup N And Spin Flavor Decomposition In The Valence Quark Region eBook

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Release : 2004
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The authors present here recent progress on the experimental study of the neutron spin structure at Jefferson Lab Hall A. They focus on two precision experiments. The physics motivation and the experimental setup will be described first. Then they present results for the neutron spin asymmetry A1(superscript n) and results for spin-flavor decomposition of the nucleon spin in the valence quark region, and preliminary results for the neutron spin structure function g2(superscript n) at low Q2.

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Page : 339 pages
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Release : 2014
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The current data for the nucleon-virtual photon longitudinal spin asymmetry A1 on the proton and neutron have shown that the ratio of the polarized-to-unpolarized down-quarkparton distribution functions, Dd=d, tends towards -1/2 at large x, in disagreement with the perturbative QCD prediction that Dd/d approaches 1 but more in line with constituent quark models. As a part of experiment E06-014 in Hall A of Jefferson Lab, double-spin asymmetries were measured in the scattering of a longitudinally polarized electron beam of energies 4.74 and 5.89 GeV from a longitudinally and transversely polarized 3He target in the deep inelastic scattering and resonance region, allowing for the extraction of the neutron asymmetry An1 and the ratios Dd/d and Du/u. We will discuss our analysis of the data and present results for A1 and g1/F1 on both 3He and the neutron, and the resulting quark ratios for the up and down quarks in the kinematic range of 0.2.

Author : David Flay
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Page : 339 pages
File Size : 31,29 MB
Release : 2014
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The current data for the nucleon-virtual photon longitudinal spin asymmetry A1 on the proton and neutron have shown that the ratio of the polarized-to-unpolarized down-quark parton distribution functions, d/d, tends towards -1/2 at large x, in disagreement with the perturbative QCD prediction that d/d approaches 1 but more in line with constituent quark models. As a part of experiment E06-014 in Hall A of Jefferson Lab, double-spin asymmetries were measured in the scattering of a longitudinally polarized electron beam of energies 4.74 and 5.89 GeV from a longitudinally and transversely polarized 3He target in the deep inelastic scattering and resonance region, allowing for the extraction of the neutron asymmetry A1n and the ratios d/d and u/u. We will discuss our analysis of the data and present results for A1 and g1/F1 on both 3He and the neutron, and the resulting quark ratios for the up and down quarks in the kinematic range of 0.2 2 2 for our deep inelastic scattering data. Invoking duality, we also extract A1n and g1n/F1n in the resonance region, characterized by 0.6 2 2. Our measurements are compared to the world data and various theoretical models and more recent predictions using the Dyson-Schwinger Equation approach. We also present analysis of the unpolarized cross section data, which contributes to the g1 spin structure function and eventually the a2 matrix element, an x2-weighted moment of g1. The extracted a2 data are compared to a Lattice QCD calculation.

Author : Melanie Leigh Cardona
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Page : 0 pages
File Size : 13,22 MB
Release : 2023
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The quest to understand how the nucleon spin is decomposed into its constituent quark and gluon spin and orbital angular momentum (OAM) components has been at the forefront of nuclear physics for decades. Due to the non-perturbative nature of Quantum Chromodynamics (QCD) - the theory describing how quarks and gluons bind together to form protons and neutrons - making absolute predictions of nucleon spin structure is generally difficult, especially as a function of its quark and gluon longitudinal momentum fraction x. Measurements involving nucleon spin structure serve as a sensitive test for QCD, including ab-initio lattice QCD calculations due to the advent of the quasi-PDF formalism, and various predictions that diverge at large-x. The neutron spin asymmetry A1n at high-x is a key observable for probing nucleon spin structure. In the valence domain (x > 0.5), sea effects are expected to be negligible, and so the total nucleon spin is considered to be carried by the valence quarks. The valence region can therefore enable us to study the role of quark OAM and other non-perturbative effects of the strong force. A1^n was measured in the deep inelastic scattering region of 0.40

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File Size : 50,46 MB
Release : 2002
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We have measured the neutron virtual photon asymmetry A1(superscript n) over the kinematic range 0.33 (less-than or equal to) x (less-than or equal to) 0.61 and 2.8 (less-than or equal to) Q2 (less-than or equal to) 4.8 (GeV/c)2. To extract A1(superscript n), longitudinal and transverse spin asymmetries have been measured for inclusive 3{rvec H}e({rvec e}, e(prime)) scattering, using a 5.7 GeV longitudinally polarized electron beam at Jefferson Lab and a high-density polarized 3He target in Hall A. Preliminary results of A1(superscript n) are presented and compared to existing data and various models, including the predictions of SU(6), broken SU(6) constituent quark models and perturbative QCD based models.

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File Size : 31,14 MB
Release : 2004
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Recent progress from Jefferson Lab has significantly improved our understanding of the nucleon spin structure in the high-x region. Results from two experiments in Hall A are presented. The first experiment is a precision measurement of the neutron spin asymmetry, A1(superscript n), in the high-x (valence quark) region. The results show for the first time that A1(superscript n) becomes positive at large x, strongly breaking SU(6) (spin-flavor) symmetry. The data trend is in good agreement with SU(6)-breaking valence quark models and with the fits to the previous world data. Combining the A1(superscript n) results with the world A1(superscript n) data, the up and down quark spin distributions in the nucleon were extracted. The results showed that for the proton the valence down quark spin is in the opposite direction from that of the proton, in disagreement with predictions of leading-order perturbative QCD models, which neglect quark orbital angular momentum.

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File Size : 38,70 MB
Release : 2005
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Recent precision spin structure data from Jefferson Lab have significantly advanced our knowledge of nucleon structure in the valence quark (high-x) region and improved our understanding of higher-twist effects, spin sum rules and quark-hadron duality. First, results of a precision measurement of the neutron spin asymmetry, A[sub 1][sup n], in the high-x region are discussed. The new data shows clearly, for the first time, that A[sub 1][sup n] becomes positive at high x. They provide crucial input for the global fits to world data to extract polarized parton distribution functions. Preliminary results on A[sub 1][sup p] and A[sub 1][sup d] in the high-x region have also become available. The up and down quark spin distributions in the nucleon were extracted. The results for [Delta]d/d disagree with the leading-order pQCD prediction assuming hadron helicity conservation. Then, results of a precision measurement of the g[sub 2][sup n] structure function to study higher-twist effects are presented. The data show a clear deviation from the lead-twist contribution, indicating a significant higher-twist (twist-3 or higher) effect. The second moment of the spin structure functions and the twist-3 matrix element d[sub 2][sup n] results were extracted at a high Q[sup 2] of 5 GeV[sup 2] from the measured A[sub 2][sup n] in the high-x region in combination with existing world data and compared with a Lattice QCD calculation. Results for d[sub 2][sup n] at low-to-intermediate Q[sup 2] from 0.1 to 0.9 GeV[sup 2] were also extracted from the JLab data. In the same Q[sup 2] range, the Q[sup 2] dependence of the moments of the nucleon spin structure functions was measured, providing a unique bridge linking the quark-gluon picture of the nucleon and the coherent hadronic picture. Sum rules and generalized forward spin polarizabilities were extracted and compared with Chiral Perturbation Theory calculations and phenomenological models. Finally, preliminary results on the resonance spin structure functions in the Q[sup 2] range from 1 to 4 GeV[sup 2] were presented, which, in combination with DIS data, will enable a detailed study of the quark-hadron duality in spin structure functions.

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Page : 234 pages
File Size : 40,96 MB
Release : 2002
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This dissertation will first give an introduction to the theories and formalism of polarized deep inelastic scattering and a review of the theories of A$n\atop{1}$. Next the experiment E99-117 at JLab Hall A will be described, followed by the data analysis. The data presented greatly improve the current world fit of neutron polarized structure functions and provide valuable insight in the understanding of the neutron spin structure.