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Precision measurement of the neutron spin dependent structure functions

Yury Georgievich Kolomensky, University of Massachusetts Amherst


In experiment E154 at the Stanford Linear Accelerator Center the spin dependent structure function $g\sbsp{1}{n}(x,Q\sp2)$ of the neutron was measured by scattering longitudinally polarized 48.3 GeV electrons off a longitudinally polarized $\sp3$He target. The high beam energy allowed us to extend the kinematic coverage compared to the previous SLAC experiments to $0.014\leq x\leq0.7$ with an average $Q\sp2$ of 5 GeV$\sp2.$ We report the integral of the spin dependent structure function in the measured range to be $\int\sbsp{0.014}{0.7}dx\ g\sbsp{1}{n}(x,5\ {\rm GeV}\sp2)={-}0.036\pm0.004({\rm stat}.)\pm0.005({\rm syst}.).$ We observe relatively large values of $g\sbsp{1}{n}$ at low x that call into question the reliability of data extrapolation to $x\to0.$ Such divergent behavior disagrees with predictions of the conventional Regge theory, but is qualitatively explained by perturbative QCD. We perform a Next-to-Leading Order perturbative QCD analysis of the world data on the nucleon spin dependent structure functions $g\sbsp{1}{p}$ and $g\sbsp{1}{n}$ paying careful attention to the experimental and theoretical uncertainties. Using the parameterizations of the helicity-dependent parton distributions obtained in the analysis, we evolve the data to $Q\sp2$ = 5 GeV$\sp2,$ determine the first moments of the polarized structure functions of the proton and neutron, and find agreement with the Bjorken sum rule.

Subject Area

Particle physics|Nuclear physics

Recommended Citation

Kolomensky, Yury Georgievich, "Precision measurement of the neutron spin dependent structure functions" (1997). Doctoral Dissertations Available from Proquest. AAI9737551.