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

The cross section for quasielastic 12C(e, e'p) scattering has been measured at momentum transfer Q~ = 1, 3, 5 , and 6.8 (Gev/c) ' [I] have suggested that, at sufficiently high momentum transfer, the final (and initial) state interactions of hadrons with the nuclear medium should be reduced, leading to the phenomenon termed "color transparency." Although the arguments were originally formulated within the context of perturbative QCD (high momentum transfer approximation of the strong interaction), recent work [2] indicates that this phenomenon occurs in a wide variety of model calculations with nonperturbative reaction mechanisms.The requirements for the existence of color transparency have been discussed recently [2] and are briefly summarized here. First, high momentum transfer scattering should take place via selection of amplitudes in the initial and final state hadrons characterized by a small transverse size (much smaller than the hadron radius). Secondly, this small object should be "color neutral" outside of this small radius in order not to radiate gluons (which would lead to inelasticity). The object, being small and color neutral, would then have reduced inter-003 1 -9007/94/72( 1 3)/1986(4)$06.00

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.

A newly obtained sample of inclusive electron-nucleon scattering data has been analyzed for precision tests of quark-hadron duality. The data are in the nucleon resonance region, and span the range 0.3 , Q 2 , 5.0 ͑GeV͞c͒ 2 . Duality is observed both in limited and extended regions around the prominent resonance enhancements. Higher twist contributions to the F 2 structure function are found to be small on average, even in the low Q 2 regime of ഠ0.5 ͑GeV͞c͒ 2 . Using duality, an average scaling curve is obtained. In all cases, duality appears to be a nontrivial property of the nucleon structure function.PACS numbers: 13.60. Hb, 12.38.Qk The interpretation of the resonance region in inclusive electron-proton scattering and its possible connection with deep inelastic scattering has been a subject of interest for nearly three decades since quark-hadron duality ideas, which successfully described hadron-hadron scattering [1], were first extended to electroproduction. Bloom and Gilman [2] showed that it was possible to equate the nucleon resonance region structure function nW 2 ͑n, Q 2 ͒ (at some typically low Q 2 value) to the structure function F 2 in the deep inelastic regime of electron-quark scattering (at some higher value of Q 2 ). These structure functions are obtained from inclusive electron-nucleon scattering where the substructure of the nucleon is probed with virtual photons of mass-squared 2Q 2 and energy n. The resonance structure function was demonstrated to be equivalent in average to the deep inelastic one, with these averages obtained over the same range in a scaling variable v 0 1 1 W 2 ͞Q 2 , where W is the invariant mass. Bloom and Gilman's quark-hadron duality qualitatively explained the data in the range 1 # Q 2 # 10 ͑GeV͞c͒ 2 . This relationship between resonance electroproduction and the scaling behavior observed in deep inelastic scattering suggests a common origin for both phenomena. Inclusive deep inelastic scattering on nucleons is a firmly established tool for the investigation of the quark-parton model. At large enough values of W and Q 2 , quantum chromodynamics (QCD) provides a rigorous description of the physics that generates the Q 2 behavior of the nucleon structure function F 2 nW 2 . The well-known logarithmic scaling violations in the F 2 structure function of the nucleon, predicted by asymptotic freedom, played a crucial role in establishing QCD as the accepted theory of strong interactions [3,4]. However, as Q 2 decreases, the description of the nucleon's structure cannot be expressed in terms of single parton densities with simple logarithmic behavior in Q 2 . Inverse power violations in Q 2 , physically representing initial and final state interactions between the struck quark and the remnants of the target (termed higher twist effects), must be taken into account as well.An analysis of the resonance region in terms of QCD was first presented in [5,6], where Bloom and Gilman's approach was reinterpreted, and the integrals of the average scaling curves were equated to the ...

We report the first measurement of the parity-violating asymmetry in elastic electron scattering from the proton. The asymmetry depends on the neutral weak magnetic form factor of the proton which contains new information on the contribution of strange quark-antiquark pairs to the magnetic moment of the proton. We obtain the value G Z M 0.34 6 0.09 6 0.04 6 0.05 n.m. at Q 2 0.1 ͑GeV͞c͒ 2 . [S0031-9007(97)03181-5] PACS numbers: 13.60. Fz, 11.30.Er, 13.40.Gp, 14.20.Dh The measurement of strange quark-antiquark (ss) effects in the nucleon offers a unique window to study the effects of the qq "sea" at low momentum transfers. This information is an important clue to the dynamical effects of QCD that are responsible for form factors in the nonperturbative regime, and may lead to new insight into the origins of these effects.It has been shown [1] that the neutral weak current can be used to determine the ss contributions to nucleon form factors. The magnetic moment is one important nucleon property that can be studied in this fashion. The neutral weak magnetic form factor of the proton can be measured in parity-violating electron scattering, [2], thus providing information on the ss content of the nucleon's magnetic moment. In this Letter, we report the first such measurement and obtain the first direct experimental data relevant to determination of the strange magnetic moment of the proton.To lowest order (tree-level), the neutral weak magnetic form factor of the proton G Z M can be related to nucleon electromagnetic form factors and a contribution from strange quarks: As mentioned above, the quantity G Z M for the proton can be measured via elastic parity-violating electron scattering at backward angles [2]. The difference in cross sections for right and left handed incident electrons arises from interference of the electromagnetic and neutral weak amplitudes, and so contains products of electromagnetic and neutral weak form factors. The expression for elastic scattering from the proton is given by