[en] The reaction γp → π⁺ K^- K⁺n was studied at Jefferson Lab using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S = +1 and mass M = 1555 ± 10 MeV/c² was observed in the nK⁺ invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM = 26 MeV/c²), and its statistical significance is 7.8 ± 1.0 σ. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by a chiral soliton model for the Θ⁺ baryon. In addition, the pK⁺ invariant mass distribution was analyzed in the reaction γ p → K^- K⁺p with high statistics in search of doubly-charged exotic baryon states. No resonance structures were found in this spectrum

[en] New cross sections for the reaction ep → e(prime)ηp are reported for total center of mass energy W=1.5--2.3 GeV and invariant squared momentum transfer Q²=0.13--3.3 GeV². This large kinematic range allows extraction of new information about response functions, photocouplings, and ηN coupling strengths of baryon resonances. A sharp structure is seen at W ∼ 1.7 GeV. The shape of the differential cross section is indicative of the presence of a P-wave resonance that persists to high Q². Improved values are derived for the photon coupling amplitude for the S₁₁(1535) resonance. The new data greatly expands the Q² range covered and an interpretation of all data with a consistent parameterization is provided

[en] The reaction ²H(e,e(prime) p)n has been studied with full kinematic coverage for photon virtuality 1.75 < 5.5 ∼ GeV². Comparisons of experimental data with theory indicate that for very low values of neutron recoil momentum (p_n < 100 MeV/c) the neutron is primarily a spectator and the reaction can be described by the plane-wave impulse approximation. For 100 < 750 MeV/c proton-neutron rescattering dominates the cross section, while Δ production followed by the NΔ → NN transition is the primary contribution at higher momenta