Measurements of the electroproduction reaction e-+ pe -AX' f n carried out at the Wilson Synchrotron Laboratory a r e reported. For fixed virtual photon-hadron center-of-mass energy, W=2.67 GeV, data are presented with the mass of the virtual photon, -k 2 , centered at 0.6, 1.2, and 2.0 G~v'. At the central -k 2 =1.2 (GeV)' point, results are also given for W =2.15 GeV. For the W =2.67, -k 2 = 1.2 Gev2 setting, an angular scan is presented and the longitudinal transverse-interference term is extracted. The data are compared with an electric Born-model calculation of Berends which has a s its only free parameter the pion electromagnetic form factor. The theory is used to extract new results for the pion form factor up to -k 2 =2.0 G~v'.
We report measurements of kaon electroproduction from hydrogen and deuterium targets carried out at the Wilson Synchrotron Laboratory at Cornell IJniversity. The reactions y,,p--. K +xo, K 'A, and K '2' were studied in the kinematic region 2.15 5 W 5 3.1 GeV and 1.2 < Q' < 4.0 GeV' as a function of Q 2 , W, and w. The Kcross sections fall much more rapidly with increasing Q than the K + A cross sections 50 that K A Z o /~~+ O as Q 2 increases.
We report measurements of the electroproduction of cp mesons from hydrogen at Q 2 values of 0.23, 0.43, and 0.97 GeV 2 with \t\ varying from 0.125 to 1.3 GeV 2 at'each Q 2 point. The data show no evidence for a Q 2 dependence of the slope of the t distribution; the forward cross section falls with increasing Q 2 as the square of the cp propagator; the decay angular distributions agree with the predictions of s-channel helicity conservation; and the ratio of the longitudinal to the transverse component increases linearly withQ 2 .Theoretical considerations imply that the hadronic size of the photon decreases as the photon becomes increasingly spacelike and massive. 1 " 3 Some measurements of p electroproduction which suggest that the t dependence becomes flatter as Q 2 increases support this photon-shrinkage hypothesis. 4 ' 5 However, since the shape of the p mass distribution is not well understood and in general is t dependent, there is no well-defined method for subtracting a substantial nonresonant 7T-7T background. As a result the experimental evidence for photon shrinkage is at best obscure.This Letter reports an experiment in which the electroproduction of cp mesons was observed over a range of \t\ from 0.125 to 1.3 GeV 2 at several values of Q 2 . Because it is composed dominantly of strange quarks, the cp meson is expected to be produced primarily by a diffractive process. 6 ' 7 Thus not only does cp electroproduction give a further test of the vector-dominance model, but the narrow width and diffractive production of the cp make it an ideal vehicle to test for photon shrinkage.The apparatus consisted of two magnetic spectrometers. One measured the momentum and angle of the scattered electron, thus giving the mass, -Q 2 , and energy, v, of the virtual photon. The electron was identified with a lead-Lucite shower counter. The other spectrometer measured the two charged kaons from the decay cp -~K + K~. A more complete description of the spectrometer system is given by Browman et al. 8
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