[PDF] Precision Measurement Of The Neutron Spin Structure Function eBook

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File Size : 38,89 MB
Release : 2001
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In experiment E154 at the Stanford Linear Accelerator Center the spin dependent structure function g[sub 1][sup n] (x, Q[sup 2]) of the neutron was measured by scattering longitudinally polarized 48.3 GeV electrons off a longitudinally polarized[sup 3]He target. The high beam energy allowed the author to extend the kinematic coverage compared to the previous SLAC experiments to 0.014[le] x[le] 0.7 with an average Q[sup 2] of 5 GeV[sup 2]. The author reports the integral of the spin dependent structure function in the measured range to be[integral][sub 0.014][sup 0.7] dx g[sub 1][sup n](x, 5 GeV[sup 2])=[minus]0.036[+-] 0.004(stat.)[+-] 0.005(syst.). The author observes relatively large values of g[sub 1][sup n] at low x that call into question the reliability of data extrapolation to x[r-arrow] 0. Such divergent behavior disagrees with predictions of the conventional Regge theory, but is qualitatively explained by perturbative QCD. The author performs a Next-to-Leading Order perturbative QCD analysis of the world data on the nucleon spin dependent structure functions g[sub 1][sup p] and g[sub 1][sup n] paying careful attention to the experimental and theoretical uncertainties. Using the parameterizations of the helicity-dependent parton distributions obtained in the analysis, the author evolves the data to Q[sup 2]= 5 GeV[sup 2], determines the first moments of the polarized structure functions of the proton and neutron, and finds agreement with the Bjorken sum rule.

Author : T. Smith
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Page : 205 pages
File Size : 35,69 MB
Release : 2003
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This thesis describes a precision measurement of the neutron spin dependent structure function, g{sub 1}{sup n}(x). The measurement was made by the E154 collaboration at SLAC using a longitudinally polarized, 48.3 GeV electron beam, and a {sup 3}He target polarized by spin exchange with optically pumped rubidium. A target polarization as high as 50% was achieved. The elements of the experiment which pertain to the polarized {sup 3}He target will be described in detail in this thesis. To achieve a precision measurement, it has been necessary to minimize the systematic error from the uncertainty in the target parameters. All of the parameters of the target have been carefully measured, and the most important parameters of the target have been measured using multiple techniques. The polarization of the target was measured using nuclear magnetic resonance techniques, and has been calibrated using both proton NMR and by measuring the shift of the Rb Zeeman resonance frequency due to the {sup 3}He polarization. The fraction of events which originated in the {sup 3}He, as measured by the spectrometers, has been determined using a physical model of the target and the spectrometers. It was also measured during the experiment using a variable pressure {sup 3}He reference cell in place of the polarized {sup 3}He target. The spin dependent structure function g{sub 1}{sup n}(z) was measured in the Bjorken x range of 0.014