[en] We have measured the ³He(e,e^'pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum p_tot. For pair relative momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low p_tot and rises to approximately 0.5 at large p_tot. This shows the dominance of tensor over central correlations at this relative momentum.

[en] The results of the SERP-E-184 experiment at the U-70 accelerator (IHEP, Protvino) are presented. Interactions of the 70GeV proton beam with carbon, silicon and lead targets were studied to detect decays of charmed D"0, anti D"0, D"+, D"- mesons and Λ_c"+ baryon near their production threshold. Measurements of lifetimes and masses have shown a good agreement with PDG data. The inclusive cross-sections of charm production and their A-dependences have been obtained. The yields of these particles are compared with the theoretical predictions and the data of other experiments. The measured cross-section of the total open charm production (σ_t_o_t(c anti c) = 7.1 ± 2.3(stat) ± 1.4(syst) μb/nucleon) at the collision c.m. energy √s = 11.8 GeV is well above the QCD model predictions. The contributions of different kinds of charmed particles to the total cross-section of the open charm production in proton-nucleus interactions vary with energy. (orig.)

[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

[en] The cross section and decay angular distributions for the coherent φ meson photoproduction on the deuteron have been measured for the first time up to a squared four-momentum transfer t =(p_γ-p_φ)² = -2 GeV²/c², using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cross sections are compared with predictions from a re-scattering model. In a framework of vector meson dominance, the data are consistent with the total φ-N cross section σ_φN at about 10 mb. If vector meson dominance is violated, a larger σ_φN is possible by introducing larger t-slope for the φN → φN process than that for the γN → φN process. The decay angular distributions of the φ are consistent with helicity conservation

[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

[en] For the first time, the reaction gamma d -> Lambda n K+ has been analyzed in order to search for the exotic pentaquark baryon Theta+(1540). The data were taken at Jefferson Lab, using the Hall-B tagged-photon beam of energy between 0.8 and 3.6 GeV and the CEBAF Large Acceptance Spectrometer (CLAS). No statistically significant structures were observed in the nK+ invariant mass distribution. The upper limit on the gamma d -> Lambda Theta+ integrated cross section has been calculated and found to be between 5 and 25 nb, depending on the production model assumed. The upper limit on the differential cross section is also reported