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

Proton propagation in nuclei was studied using the (e,elp ) reaction in the quasifree region. The coincidence (e,elp) cross sections were measured at an electron angle of 50.4" and proton angles of 50. lo, 58.2", 67.9", and 72.9" for I2C, "~1 , 58Ni, and I8'Ta targets at a beam energy of 779.5 MeV. The average outgoing proton energy was 180 MeV. The ratio of the ( e , e l p ) yield to the simultaneously measured (e, e') yield was compared to that calculated in the plane-wave impulse approximation and an experimental transmission defined. These experimental transmissions are considerably larger (a factor of -2 for 1 8 '~a ) than those one would calculate from the free N-N cross sections folded into the nuclear density distribution. A new calculation that includes medium effects (N-N correlations, density dependence of the N-N cross sections and Pauli suppression) accounts for this increase.

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Electroproduction of the A isobar in C and Fe has been studied for incident electrons with energies between 0.6 and 1.6 GeV. A longitudinal-transverse decomposition of the inclusive cross section has been made for qj =0.1 (GeV/c) 2 . The residual longitudinal cross sections measured do not provide the additional strength needed above the quasifree region to satisfy the Coulomb sum rule. The transverse cross sections are in good agreement with data from photoabsorption.PACS numbers: 25.30.Fj Excitation of the A(3,3) resonance is the dominant feature of electromagnetic and hadronic interactions with nuclei in the region of energy transfer between pion threshold and 500 MeV. Because of strong interactions with other nucleons in the nuclear interior, one expects the A to be broadened and possibly shifted in energy when excited as a constituent nucleon in nuclear matter. The nuclear response in inelastic electron scattering has been studied 1 " 3 in the A region for energy transfers to the nucleus up to 550 MeV. To date, theoretical models for electron scattering have not given a satisfactory description of the data. 4 Although calculations which include nuclear-medium effects do predict a reduction of the peak cross section and a spreading of the A width, they do not account for the -34% enhancement in the integrated strength which O'Connell et al. 4 observe in the A region. It has been speculated that the origin of this enhancement may be a "quasideuteron electrodisintegration" mode of excitation 5,6 which is strongest in the region between the quasifree peak and the A peak in the nuclear response function.The experiment reported here extends high-energy (> 1.5 GeV) measurements to the medium-heavy nucleus, Fe, and includes for the first time a longitudinaltransverse decomposition of the inclusive cross section from pion threshold through the A region. Such a decomposition is vital to understanding the nuclear response to relatively large transfers of energy and momentum. The new data provide limits on the contributions of charge-dependent processes including the lond\ dndco ^M 1 9/f R L (q,(a) + qi + tan 2 -gitudinal tail of quasifree scattering into the A region. Because A excitation on the free nucleon results from a transverse yNA coupling, experimental sensitivity to A processes is increased in the transverse component of the inclusive cross section.The experiment was performed at the Stanford Linear Accelerator Laboratory with the NPAS (Nuclear Physics at SLAC) facility. Electron beams with energies of 653, 1300, 1500, and 1650 MeV were scattered from natural targets of C and Fe. Scattered electrons were observed in the 8-GeV/c spectrometer whose detector system includes a gas Cherenkov counter, ten planes of wire chambers, and a total-absorbing segmented leadglass shower detector array. The thicknesses of the carbon and iron targets were 324 and 122 mg/cm 2 , respectively. Observation of elastic scattering from a hydrogen target provided the absolute calibration of the spectrometer. Cross sections for the C ...