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Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function ~(x, Q2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target. The data cover the kinematic range 0.023 < x < 0.6 and 1 (GeV/c) 2 < Q2 < 15 (GeV/c) 2. The integral fo~i0623 ~(x) dx evaluated at a fixed Qz of 2.5 (GeV/c) 2 is-0.0344-0.013(stat.)+0.005(syst.). Assuming Regge behavior at low x, the first moment F'~ = fl ~(x)dx is-0.037 ± 0.013(stat.)±0.005(syst.)±0.006(extrapol.

A general framework for applying radiative corrections to (e,eЈp) coincidence reactions at GeV energies is presented, with special emphasis to higher-order bremsstrahlung effects, radiation from the scattered hadron, and the validity of peaking approximations. The sensitivity to the assumptions made in practically applying radiative corrections to (e,eЈp) data is extensively discussed. The general framework is tested against experimental data of the 1 H(e,eЈp) reaction at momentum transfer values larger than 1.0 (GeV/c) 2 , where radiative processes become a dominant source of uncertainty. The formulas presented here can easily be modified for any other electron-induced coincidence reaction.

The (e, e 0 p) reaction was studied on targets of C, Fe, and Au at momentum transfers squared Q 2 of 0.6, 1.3, 1.8, and 3.3 GeV 2 in a region of kinematics dominated by quasifree electron-proton scattering. Missing energy and missing momentum distributions are reasonably well described by plane wave impulse approximation calculations with Q 2 and A dependent corrections that measure the attenuation of the final state protons. [S0031-9007 (98) The (e, e 0 p) reaction with nearly free electron-proton kinematics (quasifree) has proven to be a valuable tool to study the propagation of nucleons in the nuclear medium [1][2][3]. The relatively weak interaction of the electron with the nucleus allows the electrons to penetrate the nuclear interior and knock out protons. These studies complement nucleon-induced measurements of proton propagation in nuclei which give more emphasis to the nuclear surface. This paper reports the first results of a systematic study of the quasifree knockout of protons of 300-1800 MeV kinetic energy from carbon, iron, and gold targets. This energy range includes the minimum of the nucleon-nucleon (N-N) total cross section, the rapid rise in this cross section with energy above the pion production threshold, and extends to the long plateau in the energy dependence of the N-N total cross section. These features of the N-N interaction would be expected to be reflected in the energy dependence of attenuation of protons as they pass 5072 0031-9007͞98͞80(23)͞5072(5)$15.00

We report on precision measurements of the elastic cross section for electron-proton scattering performed in Hall C at Jefferson Lab. The measurements were made at 28 distinct kinematic settings covering a range in momentum transfer of 0.4 < Q 2 < 5.5 (GeV/c) 2 . These measurements represent a significant contribution to the world's cross section data set in the Q 2 range where a large discrepancy currently exists between the ratio of electric to magnetic proton form factors extracted from previous cross section measurements and that recently measured via polarization transfer in Hall A at Jefferson Lab. This data set shows good agreement with previous cross section measurements, indicating that if a here-to-fore unknown systematic error does exist in the cross section measurements then it is intrinsic to all such measurements.

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Spin transfer in deep-inelastic ⌳ electroproduction has been studied with the HERMES detector using the 27.6 GeV polarized positron beam in the DESY HERA storage ring. For an average fractional energy transfer ͗z͘ϭ0.45, the longitudinal spin transfer from the virtual photon to the ⌳ has been extracted. The spin transfer along the ⌳ momentum direction is found to be 0.11Ϯ0.17(stat)Ϯ0.03(syst); similar values are found for other possible choices for the longitudinal spin direction of the ⌳. This result is the most precise value obtained to date from deep-inelastic scattering with charged lepton beams, and is sensitive to polarized up quark fragmentation to hyperon states. The experimental result is found to be in general agreement with various models of the ⌳ spin content, and is consistent with the assumption of helicity conservation in the fragmentation process.