Electromagnetic production ofKΣon the nucleon near threshold

Abstract

Photo- and electroproduction of $K\Sigma$ have been investigated near their production thresholds by using an effective Lagrangian approach. For this purpose, the background amplitude is constructed from suitable Feynman diagrams, whereas the resonance terms are calculated by means of the Breit-Wigner form of multipoles. Experimental data available in the proton channels ($K^+\Sigma^0$ and $K^0\Sigma^+$) with energies up to 50 MeV above the thresholds have been utilized to extract the unknown parameters. In these proton channels the calculated observables fit nicely the experimental data, whereas in the neutron channels ($K^+\Sigma^-$ and $K^0\Sigma^0$) the predicted observables contain some uncertainties due to the the uncertainties in the values of helicity photon couplings. To this end, new $K^0\Sigma^+$ photoproduction data are urgently required. The present analysis indicates the validity of the $P_\Lambda = -\frac{1}{3} P_\Sigma$ relation derived a long time ago. In the electroproduction sector the present analysis confirms the smooth transition between photoproduction and low $Q^2$ electroproduction data. The effect of new Crystal Ball data is shown to be mild at the backward angles. It is also found that the electroproductions of $K^0\Sigma^+$ and $K^0\Sigma^0$ are practically not the suitable reactions for investigating the $K^0$ charge form factor, since the effect is small.