CLAS $$\varvec{N^*}$$ Excitation Results from Pion and Kaon Electroproduction

Abstract

The study of the structure of excited nucleon $$N^*$$ states using the electroproduction of exclusive reactions is important for exploring the non-perturbative strong interaction. The electrocoupling amplitudes of $$N^*$$ states for masses below $$W=1.8$$ GeV have been determined from analyses of CLAS $$\pi N$$ , $$\eta N$$ , and $$\pi \pi N$$ data at four momentum transfers $$Q^2$$ up to 5 GeV $$^2$$ . These studies have made it apparent that consistency of the results from independent analyses of multiple exclusive channels with different couplings and non-resonant backgrounds but the same $$N^*$$ electroexcitation amplitudes, is necessary to have confidence in the results. For the hadronic couplings, many high-lying $$N^*$$ states preferentially decay through the $$\pi \pi N$$ channel instead of the $$\pi N$$ channel. Therefore, data from the KY channels already measured with CLAS will be crucial to provide an independent analysis to compare the extracted electrocouplings for the high-lying $$N^*$$ states against those determined from the $$\pi N$$ and $$\pi \pi N$$ channels. These comparisons await the development of suitable reaction models. Starting in 2018, a program to study the structure of $$N^*$$ states in various exclusive electroproduction channels using the new CLAS12 spectrometer will get underway. These studies will probe the structure of these states for masses W up to 3 GeV and $$Q^2$$ up to 12 GeV $$^2$$ , thus providing a means to access $$N^*$$ structure information spanning a broad regime encompassing both low and high energy degrees of freedom.