We have measured exclusive pa, w , and 4 meson electroproduction at the Cornell Wilson Synchrotron. The final data sample included 4637 four-constraint e +p-e +a+ +a-+p events, with incident energy E = 11.5 GeV and electroproduction variables Q2 and W in the region 0.7 < Q2 <4 G~V~ and 1.9 < W < 4 GeV. We find that the width of the forward po diffraction peak increases rapidly as the lifetime of the intermediate hadron states decreases below CAT= 1 fm and that the peak is wider for longitudinal p' than it is for transverse pa. The longitudinal-transverse cross-section ratio R,=uL/uT, obtained assuming s-channel helicity conservation, becomes constant at high Q ' . At fixed W the diffractive vector-meson-dominance (VMD) model reproduces the Q dependence of our cross section, U = ( U T + E U L ), but is is not able to account for the rapid decrease in the cross section with increasing W we observe. We find that u,/up depends on W but is independent of Q2 for 0 . 7 < Q2 < 3 G~V~ and 2.2 < W < 3.7 GeV. However, a, is substantially larger than the diffractive VMD cross section. Our results for ad are consistent with the Q2 dependence of the diffractive VMD model for 0.8 < Q2 < 4 GeV2 and 2 < W < 3.7 GeV, but this model again fails to predict the W dependence we observe. D. G. CASSEL et al. WATER. PROPORTIONAL WIRE COUNTERS--J CHAMBERS

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