Spin structure measurements from E143 at SLAC

Measurements were made of the proton and deuteron spin structure functions g{sub 1}{sup p} and g{sub 1}{sup d} at beam energies of 29.1, 16.2, and 9.7 GeV, and g{sub 2}{sup p} and g{sub 2}{sup d} at a beam energy of 29.1 GeV. The integrals {Lambda}{sub p} = {integral}{sub 0}{sup 1} g{sub 1}{sup p} (x, Q{sup 2})dx and {Lambda}{sub d} = {integral}{sub 0}{sup 1} g{sub 1}{sup d}(x, Q{sup 2})dx were evaluated at fixed Q{sup 2} = 3 (GeV/c){sup 2} using the 29.1 GeV data to yield {Lambda}{sub p} = 0.127 {+-} 0.004(stat.) {+-} 0.010(syst.) and {Lambda}{sub d} = 0.041 {+-} 0.003 {+-} 0.004. The Q{sup 2} dependence of the ratio g{sub 1}/F{sub 1} was studied and found to be small for Q{sup 2} > 1 (GeV/c){sup 2}. Within experimental precision the g{sub 2} data are well-described by the twist-2 contribution, g{sub 2}{sup WW}. Twist-3 matrix elements were extracted and compared to theoretical predictions. The asymmetry A{sub 2} was measured and found to be significantly smaller than the positivity limit {radical}R for both proton and deuteron targets. A{sub 2}{sup p} is found to be positive and inconsistent with zero

Next-to-Leading order approximation of polarized valon and parton distributions

Polarized parton distributions and structure functions of the nucleon are analyzed in the improved valon model. The valon representation provides a model to represent hadrons in terms of quarks, providing a unified description of bound state and scattering properties of hadrons. Polarized valon distributions are seen to play an important role in describing the spin dependence of parton distributions in the leading order (LO) and next-to-leading order (NLO) approximations. In the polarized case, a convolution integral is derived in the framework of the valon model. The Polarized valon distribution in a proton and the polarized parton distributions inside the valon are necessary to obtain the polarized parton distributions in a proton. Bernstein polynomial averages are used to extract the unknown parameters of the polarized valon distributions by fitting to the available experimental data. The predictions for the NLO calculations of the polarized parton distributions and proton structure functions are compared with the LO approximation. It is shown that the results of the calculations for the proton structure function, $xg_1^p$, and its first moment, $\Gamma_{1}^p$, are in good agreement with the experimental data for a range of values of $Q^{2}$. Finally the spin contribution of the valons to the proton is calculated.Comment: 22 pages, 7 figures. Published in Journal of High Energy Physics (JHEP

Recent SLAC measurements of the spin dependent structure functions for the proton and neutron

The authors present results from SLAC experiments E142 and E143 for the spin dependent structure functions of the proton g{sub 1}{sup p}(x, Q{sup 2}) and neutron g{sub 1}{sup n}(x,Q{sup 2}) measured in deep inelastic scattering of polarized electrons from a polarized target. Experiment E142 measures {integral}{sub 0}{sup 1} g{sub 1}{sup n}(x)dx = {minus}0.022 {+-} 0.011 at = 2 (GeV/c){sup 2} using a polarized {sup 3}He target. Experiment E143 measures {integral}{sub 0}{sup 1} g{sub 1}{sup p}(x)dx = 0.129 {+-} 0.011 at = 3 (GeV/c){sup 2} using a polarized NH{sub 3} target. These results are combined at Q{sup 2} = 3 (GeV/c){sup 2} to yield {integral}{sub 0}{sup 1} [g{sub 1}{sup p}(x) {minus} g{sub 1}{sup n}(x)]dx = 0.151 {+-} 0.015. The Bjorken sum rule predicts 0.171 {+-} 0.008

Measurements of the Proton and Deuteron Spin Structure Functions g1 and g2

SLAC-PUB-7753, February 1998Measurements are reported of the proton and deuteron spin structure functions gp1 and gd1 at beam energies of 29.1, 16.2, and 9.7 GeV, and gp2 and gd2 at a beam energy of 29.1 GeV.Work supported in part by Department of Energy contract DE-AC03-76SF00515

Measurements of the Proton and Deuteron Spin Structure Function g2 and Asymmetry A2

Submitted to Physical Review Letters. The article of record may be found at http://dx.doi.org/10.1103/PhysRevLett.76.587.We have measured proton and deuteron virtual photon-nucleon asymmetries Ap2 and Ad2 and structure functions gp2 and gd2 over the range 0.03<x<0.8 and 1.3<Q2<10(GeV/c)2 by inelastically scattering polarized electrons off polarized ammonia targets. Results for A2 are significantly smaller than the positivity limit R‾‾√ for both targets. Within experimental precision the g2 data are well described by the twist-2 contribution, gWW2. Twist-3 matrix elements have been extracted and are compared to theoretical predictions.Work supported in part by Department of Energy contract DE-AC03-76SF00515

Precision measurement of the proton spin structure function g(p1)

We have measured the ratio (gi) /F(gi) over the range 0.029 ( x ( 0.8 and 1.3 (Q+/- ( 10 (GeV/c) using deep-inelastic scattering of polarized electrons from polarized ammonia. An evaluation of the integral fo g+/_ (x, Q2) dx at fixed Q2 = 3 (GeV/c)2 yields 0.127 +/- 0.004(stat) +/- 0.010(syst), in agreement with previous experiments, but well below the Ellis-Jaffe sum rule prediction of 0.160 +/- 0.006. In the quark-parton model, this implies Aq = 0.27 +/- 0.10.This work was supported by Department of Energy Contracts No. DE-AC05-84ER40150 (CEBAF), No. W-2795-Eng-48 (LLNL), No. DE-AC0376SF00515 (SLAC), No. DE-FG03-88ER40439 (Stanford), No. DE-FG05-88ER40390 and No. DEFG05-86ER4026 (Virginia), and No. DE-AC02-76ER00881 (Wisconsin); by National Science Foundation Grants No. 9114958 (American), No. 9307710 (Massachusetts), No. 9217979 (Michigan), No. 9104975 (ODU) and No. 9118137 (U. Penn.); by the Schweizersche Nationalfonds (Basel); by the Commonwealth of Virginia (Virginia); by the Centre NAtional de la Recherche Scientifique and the Commissariat a l'Energie Atomique (French groups); and by the Japanese Ministry of Education, Science and Culture (Tohoku)

Precision measurement of the deuteron spin structure function gd1

We report on a high-statistics measurement of'. the deuteron spin structure function g(di) at a beam energy of 29 GeV in the kinematic range 0.029 < x < 0.8 and 1 < Q2 < IO (GeV / c) (2) • The integral r(di) = f(1o) g(di) dx evaluated at fixed Q2 = 3 (GeV/c) 2 gives 0.042 ± 0.003(stat) ± 0.004(syst). Combining this result with our earlier measurement of g(di), we find r(pi) - r(nt) = 0.163 ± O.OIO(stat) ± 0.016(syst), which agrees with the prediction of the Bjorken sum rule with O(a(3x)) corrections, r(pi) - r(ni) = 0.171 ± 0.008. We find the quark contribution to the proton helicity to be liq = 0.30 ± 0.06.This work was supported by Department of Energy Contracts No. DE-AC05-84ER40150 (CEBAF), No. W-2795-Eng-48 (LLNL), No. DE-AC0376SF00515 (SLAC), No. DE-FG03-88ER40439 (Stanford), No. DE-FG05-88ER40390 and No. DEFG05-86ER4026 (Virginia), and No. DE-AC02-76ER00881 (Wisconsin); by National Science Foundation Grants No. 9114958 (American), No. 9307710 (Massachusetts), No. 9217979 (Michigan), No. 9104975 (ODU) and No. 9118137 (U. Penn.); by the Schweizersche Nationalfonds (Basel); by the Commonwealth of Virginia (Virginia); by the Centre NAtional de la Recherche Scientifique and the Commissariat a l'Energie Atomique (French groups); and by the Japanese Ministry of Education, Science and Culture (Tohoku)

Measurements of R = σL/σT for 0.03 < x < 0.1 and Fit to World Data

Measurements were made at SLAC of the cross section for scattering 29 GeV electrons from carbon at a laboratory angle of 4.58, corresponding to 0.03-x-0.1 and 1.3-Q2-2.7 GeV2. Values of RssLrsT were extracted in this kinematic range by comparing these data to cross sections measured at a higher beam energy by the NMC collaboration. The results are in reasonable agreement with pQCD calculations and with extrapolations of the R1990 parameterization of previous data. A new fit is made including these data and other recent results. q1999 Published by Elsevier Science B.V. All rights reserved.This work was supported by Department of Energy contracts: No. W-2705-Eng-48 ŽLLNL., No. DE-AC03-76SF00515 ŽSLAC., No. DE-FG03- 88ER40439 ŽStanford., Nos. DE-FG05-88ER40390 and DEFG05-86ER40261 ŽVirginia., and No. DE- AC02-76ER00881 ŽWisconsin.; by National Science Foundation Grants No. 9114958 ŽAmerican., No. 9307710 ŽMassachusetts., No. 9217979 ŽMichigan., and No. 9104975 ŽODU.; by the Schweizerische Nationalfonds ŽBasel.; by the Commonwealth of Virginia; and by the Ministry of Science, Culture and Education of Japan ŽTohoku..This work was supported by Department of Energy contracts: No. W-2705-Eng-48 LLNL., No. DE-AC03-76SF00515 ŽSLAC., No. DE-FG03- 88ER40439 Stanford., Nos. DE-FG05-88ER40390 and DEFG05-86ER40261 Virginia., and No. DE- AC02-76ER00881 Wisconsin.; by National Science Foundation Grants No. 9114958 American., No. 9307710 Massachusetts., No. 9217979 Michigan., and No. 9104975 ŽODU.; by the Schweizerische Nationalfonds ŽBasel.; by the Commonwealth of Virginia; and by the Ministry of Science, Culture and Education of Japan Tohoku.