Longitudinal and Transverse Cross Sections in the1H(e,e′<

Abstract

The 1 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

Electromagnetic production ofKΣon the nucleon near threshold

“…More than a decade ago, Niculescu et al [68] have measured the e + p → e ′ + K + + Λ process and found that the longitudinal cross section dσ L /dΩ at Q 2 = 0.52 GeV 2 is significantly large, almost as large as the transverse one dσ T /dΩ. In order to reproduce these data an isobar model must dramatically increases both cross sections from photon point up to a certain value of Q 2 (see Fig.…”

Electroproduction of strangeness above the resonance region

“…Q 2 dependence of σT and σL (upper plot) and σL/σT (lower plot) for the γ * + p → K + + Λ reaction, at W = 1.84 GeV. Experimental data points are from : (•, •, ⋆) : [6] and (△) : [7]. Besides our calculation, on the lower panel are also shown the models of Ref.…”

“…The signs of the K * strong coupling constants are also in accordance with SU(3). It turns out that the recent measurement [6], at Jefferson Lab, of the ratio between the Coulomb (σ L ) and the transverse (σ T ) cross-sections of the p(e, e ′ K + )Λ reaction clearly favors the Regge model over the resonance models, already in the CEBAF energy range. Fig.…”

Electromagnetic production of kaons from protons, and baryon electromagnetic form factors

“…Most of the recent data has been obtained at Jefferson Lab, either by the Hall C Collaboration [33] or by CLAS [34][35][36]. The earliest theoretical studies of electroproduction date from the mid 1970s, and were based on a simple Regge model [37].…”