[en] The electromagnetic decays of the Σ⁰(1385) and Λ(1520) hyperons were studied in photon-induced reactions γ p → K⁺ Λ(1116)γ in the CLAS detector at the Thomas Jefferson National Accelerator Facility. We report the first observation of the radiative decay of the Σ⁰(1385) and a measurement of the Λ(1520) radiative decay width. For the Σ⁰(1385) → Λ(1116)γ transition, we measured a partial width of 479 ± 120(stat)_-100⁺⁸¹(sys) keV, larger than all of the existing model predictions. For the Λ(1520) → Λ(1116)γ transition, we obtained a partial width of 167 ± 43(stat)_-12⁺²⁶(sys) keV

[en] The reaction γp → K⁺K^-p was studied at Jefferson Lab with photon energies from 1.8 to 3.8 GeV using a tagged photon beam. The goal was to search for a Θ⁺⁺ pentaquark, a narrow doubly charged baryon state having strangeness S = +1 and isospin I = 1, in the pK⁺ invariant mass spectrum. No statistically significant evidence of a Θ⁺⁺ was found. Upper limits on the total and differential production cross section for the reaction γp → K^-Θ⁺⁺ were obtained in the mass range from 1.5 to 2.0 GeV/c², with an upper limit of about 0.15 nb, 95% C.L. for a narrow resonance with a mass M_#Theta#_#sup ++# = 1.54 GeV/c². This result places a very stringent upper limit on the Θ⁺⁺ width

[en] High-quality cross sections for the reaction γd → π⁰d have been measured using the CLAS at Jefferson Lab over a wide energy range near and above the η-meson photoproduction threshold. At backward c.m. angles for the outgoing pions, we observe a resonance-like structure near E_γ = 700 MeV. Our model analysis shows that it can be explained by η excitation in the intermediate state. The effect is the result of the contribution of the N(1535)S₁₁ resonance to the amplitudes of the subprocesses occurring between the two nucleons and of a two-step process in which the excitation of an intermediate η meson dominates