B. B. Niczyporuk

Electroexcitation of the Roper resonance for 1.7<Q{sup 2}<4.5 GeV{sup 2} in e-vectorp{yields}en{pi}{sup +}

The helicity amplitudes of the electroexcitation of the Roper resonance are extracted for 1.7 < Q 2 < 4.5 GeV 2 from recent high precision JLab-CLAS cross section and longitudinally polarized beam asymmetry data for π + electroproduction on protons at W = 1.15 - 1.69 GeV. The analysis is made using two approaches, dispersion relations and a unitary isobar model, which give consistent Q 2 behavior of the helicity amplitudes for the γ* p → N(1440)P 11 transition. It is found that the transverse helicity amplitude A 1/2 , which is large and negative at Q 2 = 0, becomes large and positive at Q 2 ≃ 2GeV 2 , and then drops slowly with Q 2 . The longitudinal helicity amplitude S 1/2 , which was previously found from CLAS ep → epπ 0 , enπ + data to be large and positive at Q 2 = 0.4, 0.65 GeV 2 , drops with Q 2 . Available model predictions for γ*p → N(1440)P 11 allow us to conclude that these results provide strong evidence in favor of N(1440)P 11 as a first radial excitation of the 3q ground state. The results of the present paper also confirm the conclusion of our previous analysis for Q 2 < 1 GeV 2 that the presentation of N(1440)P 11 as a q 3 G hybrid state is ruled out.

Cascade production in the reactions {gamma}p{yields}K{sup +}K{sup +}(X) and {gamma}p{yields}K{sup +}K{sup +}{pi}{sup -}(X)

Photoproduction of the cascade resonances has been investigated in the reactions {gamma}p{yields}K{sup +}K{sup +}(X) and {gamma}p{yields}K{sup +}K{sup +}{pi}{sup -}(X). The mass splitting of the ground state ({xi}{sup -},{xi}{sup 0}) doublet is measured to be 5.4{+-}1.8 MeV/c{sup 2}, consistent with existing measurements. The differential (total) cross sections for the {xi}{sup -} have been determined for photon beam energies from 2.75 to 3.85 (4.75) GeV and are consistent with a production mechanism of Y*{yields}K{sup +}{xi}{sup -} through a t-channel process. The reaction {gamma}p{yields}K{sup +}K{sup +}{pi}{sup -}[{xi}{sup 0}] has also been investigated to search of excited cascade resonances. No significant signal of excited cascade states other than the {xi}{sup -}(1530) is observed. The cross-section results of the {xi}{sup -}(1530) have also been obtained for photon beam energies from 3.35 to 4.75 GeV.