The spin content of the proton in full QCD

We present preliminary results on the proton spin structure function in full QCD. The measurement has been done using 4 flavours of staggered fermions and an improved definition of the lattice topological charge density.Comment: 3 pages, 3 figures, contribution to Lattice-97. Latex file including espcrc2.sty. The colour of a line in the first figure has been changed to avoid problems on some printer

Evolution of Gluon Spin in the Nucleon

We examine the $Q^2$ evolution of gluon polarization in polarized nucleons. As is well known, the evolution of $\alpha_s \Delta G(Q^2)$ is negligible for typical momentum transfer variations found in experimental deep inelastic scattering. As $\alpha_s$ increases, however, the leading nonzero term in the evolution equation for the singlet first moment reduces the magnitude of the gluon spin. At low $Q^2$ the term $\alpha_s \Delta G$ can vanish, and ultimately become negative. Thus, low energy model calculations yielding negative $\Delta G$ are not necessarily in conflict with experimental evidence for positive gluon polarization at high $Q^2$.Comment: ReVTeX + psfig, 7 pages, 3 figures (postscript), accepted in Physics Letters B, ([email protected]

Review of recent results in spin physics

Recent results in polarized DIS are reviewed. Particular emphasis is placed on new measurements of transverse and longitudinal asymmetries, on the tests of the spin sum rules and on the analysis of the spin structure function $g_1$ in perturbative QCD at NLO.Comment: 15 pages, LaTex, 15 eps figures included, to be published in Proceedings of 7th Int. Workshop on Deep Inelastic Scattering and QCD (DIS99

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

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

Calculations of Higher Twist Distribution Functions in the MIT Bag Model

We calculate all twist-two, three and four parton distribution functions involving two quark correlations using the wavefunction of the MIT bag model. The distributions are evolved up to experimental scales and combined to give the various nucleon structure functions. Comparisons with recent experimental data on higher twist structure functions at moderate values of $Q^{2}$ give good agreement with the calculated structure functions.Comment: 26 pages LaTeX document, 11 figures include

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 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)