Exclusive electroproduction of K+ Lambda and K+ Sigma^0 final states at Q^2 = 0.030-0.055 (GeV/c)^2

TL;DR

This study measures exclusive K+ Lambda and K+ Sigma^0 electroproduction cross sections at low Q^2 using the Kaos spectrometer, revealing a smooth transition from photoproduction and constraining theoretical models of nucleon resonances.

Contribution

First-time measurement of these reactions at low Q^2 with the Kaos spectrometer, providing new data in an unexplored kinematic region and testing effective Lagrangian models.

Findings

Smooth Q^2 transition observed in cross sections

Strong longitudinal couplings to N* resonances are excluded

Data constrains theoretical models of nucleon resonance excitation

Abstract

Cross section measurements of the exclusive p(e,e'K+)Lambda,Sigma^0 electroproduction reactions have been performed at the Mainz Microtron MAMI in the A1 spectrometer facility using for the first time the Kaos spectrometer for kaon detection. These processes were studied in a kinematical region not covered by any previous experiment. The nucleon was probed in its third resonance region with virtual photons of low four-momenta, Q^2= 0.030-0.055 (GeV/c)^2. The MAMI data indicate a smooth transition in Q^2 from photoproduction to electroproduction cross sections. Comparison with predictions of effective Lagrangian models based on the isobar approach reveal that strong longitudinal couplings of the virtual photon to the N* resonances can be excluded from these models.