The proton and deuteron structure functions F p 2 and F d 2 are measured in inelastic muon scattering with an average beam energy of 470 GeV. The data were taken at Fermilab experiment E665 during 1991-92 using liquid hydrogen and deuterium targets. The F2 measurements are reported in the range 0:0008 < x < 0 : 6 and 0:2 < Q 2 < 75 GeV 2. These are the rst precise measurements of F2 in the low x and Q 2 range of the data. In the high x range of the data where they overlap in x and Q 2 with the measurements from NMC, the two measurements are in agreement. The E665 data also overlap in x with the HERA data, and there is a smooth connection in Q 2 between the two data sets. At high Q 2 the E665 measurements are consistent with QCDevolved leading twist structure function models. The data are qualitatively described 2 by structure function models incorporating the hadronic nature of the photon at low Q 2. The Q 2 and the W dependence of the data measure the transition in the nature of the photon between a point-like probe at high Q 2 and a hadronic object at low Q 2 .

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

The A-dependence of the quasielastic A(e, e ′ p) reaction has been studied at SLAC with 2 H, C, Fe, and Au nuclei at momentum transfers Q 2 = 1, 3, 5, and 6.8 (GeV/c) 2 . We extract the nuclear transparency T (A, Q 2 ), a measure of the average probability that the struck proton escapes from the nucleus A without interaction. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as Color Transparency. No significant rise within errors is seen for any of the nuclei studied.PACS numbers: 25.30 In 1982, Mueller and Brodsky [1] proposed that in wide angle exclusive processes, the soft initial and final state interactions (ISI and FSI) of hadrons in nuclei would vanish at high energies. This effect, originally based on arguments using perturbative QCD, is called "Color Transparency" (CT), in reference to the disappearance of the color forces between the hadrons and nuclei. Evidence for the CT effect can be sought by measurement of the nuclear transparency T , defined as the ratio of the measured cross section to the cross section expected in the limit of complete CT (i.e., no ISI or FSI), as a function of the 4-momentum transfer squared, Q 2 , and nuclear mass, A. For CT to be observable in quasielastic A(e, e ′ p) scattering, the recoiling proton must maintain its reduced interaction with other nucleons over a distance comparable to the nuclear radius. This is probed directly by measuring the A dependence of T . At low energies, T < 1 because of absorption or deflection of the hadrons by ISI and FSI with the nucleus. As the energy increases, and if CT effects begin to dominate the scattering, T should increase towards unity [2]. Some recent models of CT predict significant increases in T for Q 2 as low as 5 (GeV/c) 2 [2-6]. We present measurements of T for the reaction A(e, e ′ p) on 2 H, C, Fe, and Au nuclei at Q 2 = 1, 3, 5, and 6.8 (GeV/c) 2 .The first experiment to investigate CT was performed by Carroll et al. [7] using simultaneous measurements of A(p, 2p) and H(p, 2p) reaction rates at Brookhaven National Laboratory. Their results showed T increasing for Q 2 ≃ 3-8 (GeV/c) 2 , but then decreasing for Q 2 ≃ 8-11 (GeV/c) 2 . Because of the subsequent decrease, the rise at lower momentum transfer cannot be taken as an unambiguous signal of CT. Ralston and Pire [6] suggest that the maximum in T is due to a soft process that interferes with the perturbative QCD amplitude in free proton-proton scattering but is suppressed in the nuclear environment. Such ambiguities should be smaller in A(e, e ′ p) reactions because of the simplicity of the elementary electron-proton interaction compared to the proton-proton interaction.

The ratio of cross sections for inelastic muon scattering on xenon and deuterium nuclei was measured at very low Bjorken x (0.00002 < XBJ < 0.25). The data were taken at Fermilab experiment E665 with a 490 GeV/c muon beam incident on liquid deuterium and gaseous xenon targets. Two largely independent analysis techniques gave statistically consistent results. The xenon-to-deuterium per-nucleon cross-section ratio is constant at approximately 0.7 for XBJ below 0.003.

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