A Precision Measurement of the Spin Structure of the Proton at SLAC
E143 at SLAC Endstation A performed deep-inelastic scattering measurements of polarized electrons from polarized protons and deuterons within cryogenic {sup 15}NH{sub 3} and {sup 15}ND{sub 3}, respectively. Data were taken at incident energies of 29.1, 16.2 and 9.7 GeV, and covered the kinematical range x > 0:03 and 0:3 < Q{sup 2} < 12 (GeV/c){sup 2}. The scattered electrons were detected by two spectrometers at angles of 4.5{sup o} and 7.0{sup o}. From these data, the spin-dependent structure functions g{sub 1}{sup p}(x; Q{sup 2}) and g{sub 1}{sup d}(x; Q{sup 2}) were determined. This dissertation describes the experiment, with emphasis on the results on the proton spin structure. The integral of g{sub 1} over the range 0 < x < 1 was found to be {Gamma}{sub 1}{sup p} = 0.130 {+-} 0.003 {+-} 0.008 for the proton and {Gamma}{sub 1}{sup d} = 0.044 {+-} 0.003 {+-} 0.004 for the deuteron. Both values are in agreement with world data, and violate the Ellis-Jaffe sum rule by more than 3 standard deviations. The neutron structure function was obtained by combining proton and deuteron results, giving {Gamma}{sub 1}{sup n} = [0.035 {+-} 0.007 {+-} 0.010]. From this the integral {Gamma}{sub 1}{sup p}-{Gamma}{sub 1}{sup n} followed, yielding 0.165 {+-} 0.009 {+-} 0.016 at Q{sup 2} = 3 (GeV/c){sup 2}, in agreement with the Bjorken sum rule to within one standard deviation. The Q{sup 2}-dependence of the ratio g{sub 1}/F{sub 1} was determined to be small for Q{sup 2} > 1 (GeV/c){sup 2}, validating the assumption of no Q{sup 2}-dependence used in obtaining the integrals. A small rise with increasing Q{sup 2} was seen in the ratio for Q{sup 2} < 1 (GeV/c){sup 2}, however. The total quark contribution to the spin was found to be {Delta}q = 0.28 {+-} 0.09 for the proton, and {Delta}q = 0.32 {+-} 0.05 for the deuteron. Furthermore, a large negative spin contribution from the strange sea quarks was measured for both nucleons, giving {Delta}s = 0.10 {+-} 0.03 and {Delta}s = -0.09 {+-} 0.02 for the proton and deuteron respectively, in contradiction to the Ellis-Jaffe assumption of no polarized strange sea.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research (ER) (US)
- DOE Contract Number:
- AC03-76SF00515
- OSTI ID:
- 15083
- Report Number(s):
- SLAC-R-546; TRN: US0204540
- Resource Relation:
- Other Information: PBD: 22 Sep 1999
- Country of Publication:
- United States
- Language:
- English
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