LONGITUDINAL AND TRANSVERSE CROSS SECTIONS IN THE ¹H(E, E'K⁺)Λ REACTION

Abstract

The1 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