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 measurements of cross sections for the reaction 1 H(e,eЈK ϩ )Y , for both the ⌳ and ⌺ 0 hyperon states, at an invariant mass of Wϭ1.84 GeV and four-momentum transfers 0.5ϽQ 2 Ͻ2 (GeV/c) 2 . Data were taken for three values of virtual photon polarization ⑀, allowing the decomposition of the cross sections into longitudinal and transverse components. The ⌳ data are a revised analysis of prior work, whereas the ⌺ 0 results have not been previously reported.

The 1 H͑e, e 0 K 1 ͒L reaction was studied as a function of the squared four-momentum transfer, Q 2 , and the virtual photon polarization,´. For each of four Q 2 settings, 0.52, 0.75, 1.00, and 2.00 ͑GeV͞c͒ 2 , the longitudinal and transverse virtual photon cross sections were extracted in measurements at three virtual photon polarizations. The Q 2 dependence of the s L ͞s T ratio differs significantly from current theoretical predictions. This, combined with the precision of the measurement, implies a need for revision of existing calculations. [S0031-9007 (98) Flavor degrees of freedom provide qualitatively new tests of our understanding of baryon and meson structure. The electromagnetic production of kaons is important for further progress in many fields and subfields of physics such as hypernuclear production and spectroscopy ͑ ͑ ͑providing information complementary to that from hadronic reactions such as ͑K, p͒, ͑p, K͒, and ͑p, p 0 K͒ [1,2]͒ ͒ ͒, and some aspects of QCD model building ͑ ͑ ͑the ͑g, K͒ and the ͑e, e 0 K͒ reactions are important for an improved understanding of the basic coupling constants needed in various nucleon-meson and quark models [3]͒ ͒ ͒ to name only a few. The use of virtual photons (electroproduction) as opposed to real photons (photoproduction) offers access to a much richer body of information because both the virtual photon mass and polarization can be varied independently [4].This Letter is a report on the first results of a study of associated kaon electroproduction on hydrogen using the medium-energy, high-intensity, electron beam at the Jefferson Laboratory (formerly CEBAF). The excellent beam qualities of the CEBAF accelerator combined with precision magnetic spectrometers allowed a detailed 0031-9007͞98͞81(9)͞1805(4)$15.00

A separation of the longitudinal and transverse 12 C(e,eЈp) cross sections in the quasifree region has been performed in parallel kinematics at Q 2 of 0.64 and 1.8 GeV 2 for initial proton momentum Ͻ80 MeV. The separated transverse and longitudinal spectral functions at Q 2 ϭ0.64 GeV 2 show significant differences for missing energy between 25 and 60 MeV indicating a breakdown in the single nucleon knockout picture. The transverse spectral functions exhibit definite momentum transfer dependence.PACS number͑s͒: 25.30.Fj, 25.30.Rw

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