S. E. Rock

The spin structure function of the neutron ${\mathit{g}}_{1}^{\mathit{n}}$ has been determined over the range 0.03x0.6 at an average ${\mathit{Q}}^{2}$ of 2 (GeV/c${)}^{2}$ by measuring the asymmetry in deep inelastic scattering of polarized electrons from a polarized $^{3}\mathrm{He}$ target at energies between 19 and 26 GeV. The integral of the neutron spin structure function is found to be ${\mathcal{F}}_{0}^{1}$${\mathit{g}}_{1}^{\mathit{n}}$(x)dx=-0.022\ifmmode\pm\else\textpm\fi{}0.011. Earlier reported proton results together with the Bjorken sum rule predict ${\mathcal{F}}_{0}^{1}$${\mathit{g}}_{1}^{\mathit{n}}$(x)dx=-0.059\ifmmode\pm\else\textpm\fi{}0.019.

We report results of an electron-beam-dump search for neutral particles with masses in the range 1 to 15 MeV and lifetimes \ensuremath{\tau} between ${10}^{\mathrm{\ensuremath{-}}14}$ and ${10}^{\mathrm{\ensuremath{-}}10}$ s. No evidence was found for such an object. We fule out the existence of any 1.8-MeV pseudoscalar boson with \ensuremath{\tau}>8.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}15}$ s and an absorption cross section in matter less than 1 mb per nucleon, and exclude \ensuremath{\tau}>1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}14}$ s were its cross section to equal 50 mb per nucleon. In conjunction with measurements of the electron's anomalous magnetic moment, this experiment shows that the narrow positron peaks observed in heavy-ion collisions at the Gessellschaft fu\ifmmode\ddot\else\textasciidieresis\fi{}r Schwerionenforschung are not due to an elementary pseudoscalar.

The deep-inelastic electron-scattering cross sections per nucleon ${\ensuremath{\sigma}}_{A}$ for D, He, Be, C, A1, Ca, Fe, Ag, and Au were measured in the kinematic range $0.09<~x<~0.9$ and $2<~{Q}^{2}<~15$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ with use of electrons with energies ranging from 8 to 24.5 GeV. The ratio $\frac{{\ensuremath{\sigma}}_{A}}{{\ensuremath{\sigma}}_{\mathrm{D}}}$ is consistent with unity in the range $0.1<x<0.3$. For $0.3<x<0.8$, the ratio decreases logarithmically with atomic weight $A$, or linearly with average nuclear density. No ${Q}^{2}$ dependence in the ratio was observed over the kinematic range of the data.

Measurements are reported of the proton and deuteron spin structure functions ${g}_{1}^{p}$ and ${g}_{1}^{d}$ at beam energies of 29.1, 16.2, and 9.7 GeV, and ${g}_{2}^{p}$ and ${g}_{2}^{d}$ at a beam energy of 29.1 GeV. The integrals ${\ensuremath{\Gamma}}_{p}={\ensuremath{\int}}_{0}^{1}{g}_{1}^{p}{(x,Q}^{2})dx$ and ${\ensuremath{\Gamma}}_{d}={\ensuremath{\int}}_{0}^{1}{g}_{1}^{d}{(x,Q}^{2})dx$ were evaluated at fixed ${Q}^{2}=3(\mathrm{GeV}{/c)}^{2}$ using the full data set to yield ${\ensuremath{\Gamma}}_{p}=0.132\ifmmode\pm\else\textpm\fi{}0.003(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.009(\mathrm{syst})$ and ${\ensuremath{\Gamma}}_{d}=0.047\ifmmode\pm\else\textpm\fi{}0.003\ifmmode\pm\else\textpm\fi{}0.006.$ The ${Q}^{2}$ dependence of the ratio ${g}_{1}{/F}_{1}$ was studied and found to be small for ${Q}^{2}>1(\mathrm{GeV}{/c)}^{2}.$ Within experimental precision the ${g}_{2}$ data are well described by the twist-2 contribution, ${g}_{2}^{\mathrm{WW}}.$ Twist-3 matrix elements were extracted and compared to theoretical predictions. The asymmetry ${A}_{2}$ was measured and found to be significantly smaller than the positivity limit $\sqrt{R}$ for both proton and deuteron targets. ${A}_{2}^{p}$ is found to be positive and inconsistent with zero. Measurements of ${g}_{1}$ in the resonance region show strong variations with $x$ and ${Q}^{2},$ consistent with resonant amplitudes extracted from unpolarized data. These data allow us to study the ${Q}^{2}$ dependence of the integrals ${\ensuremath{\Gamma}}_{p}$ and ${\ensuremath{\Gamma}}_{n}$ below the scaling region.