The ${}^1\mathrm{H}\left({e,e}^{\prime }{K}^{+}\right)\Lambda$ reaction was studied as a function of the squared four-momentum transfer, $Q^2$, and the virtual photon polarization, $\varepsilon$. For each of four $Q^2$ settings, 0.52, 0.75, 1.00, and 2.00 $(\mathrm{GeV}/c{)}^2$, the longitudinal and transverse virtual photon cross sections were extracted in measurements at three virtual photon polarizations. The $Q^2$ dependence of the ${\sigma }_L/{\sigma }_T$ ratio differs significantly from current theoretical predictions. This, combined with the precision of the measurement, implies a need for revision of existing calculations.

• Received 27 March 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.1805