Transverse polarization of Σ^{+}(1189) in photoproduction on a hydrogen target in CLAS

Experimental results on the Σ+(1189) hyperon transverse polarization in photoproduction on a hydrogen target using the CLAS detector at Jefferson Laboratory are presented. The Σ+(1189) was reconstructed in the exclusive reaction γ+p→K0S+Σ+(1189) via the Σ+→pπ0 decay mode. The K0S was reconstructed in the invariant mass of two oppositely charged pions with the π0 identified in the missing mass of the detected pπ+π− final state. Experimental data were collected in the photon energy range Eγ=1.0–3.5 GeV (s√ range 1.66–2.73 GeV). We observe a large negative polarization of up to 95%. As the mechanism of transverse polarization of hyperons produced in unpolarized photoproduction experiments is still not well understood, these results will help to distinguish between different theoretical models on hyperon production and provide valuable information for the searches of missing baryon resonances

Complete measurement of three-body photo-disintegration of 3He for photon energies between 0.35 GeV and 1.55 GeV

The three-body photodisintegration of He3 has been measured with the CLAS detector at Jefferson Lab, using tagged photons of energies between 0.35 GeV and 1.55GeV. The large acceptance of the spectrometer allowed us for the first time to cover a wide momentum and angular range for the two outgoing protons. Three kinematic regions dominated by either two- or three-body contributions have been distinguished and analyzed. The measured cross sections have been compared with results of a theoretical model, which, in certain kinematic ranges, have been found to be in reasonable agreement with the data

Measurement of deeply virtual compton scattering with a polarized-proton target

The longitudinal target-spin asymmetry AUL for the exclusive electroproduction of high-energy photons was measured for the first time in ep⃗ →e′pγ. The data have been accumulated at JLab with the CLAS spectrometer using 5.7 GeV electrons and a longitudinally polarized NH3 target. A significant azimuthal angular dependence was observed, resulting from the interference of the deeply virtual Compton scattering and Bethe-Heitler processes. The amplitude of the sin ϕ moment is 0.252±0.042stat±0.020sys. Theoretical calculations are in good agreement with the magnitude and the kinematic dependence of the target-spin asymmetry, which is sensitive to the generalized parton distributions H˜ and H

Radiative decays of the Σ0(1385) and Λ+B95(1520) hyperons

The electromagnetic decays of the Σ0(1385) and Λ(1520) hyperons were studied in photon-induced reactions γp→K+Λ(1116)γ in the Large Acceptance Spectrometer 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)+81−100(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)+26−12(sys)keV

Observation of an exotic S = +1 baryon in exclusive photoproduction from the deuteron

In an exclusive measurement of the reaction γd→K+K−pn, a narrow peak that can be attributed to an exotic baryon with strangeness S=+1 is seen in the K+n invariant mass spectrum. The peak is at 1.542±0.005  GeV/c2 with a measured width of 0.021  GeV/c2 FWHM, which is largely determined by experimental mass resolution. The statistical significance of the peak is (5.2±0.6)σ. The mass and width of the observed peak are consistent with recent reports of a narrow S=+1 baryon by other experimental groups

Search for the Θ^{+} Pentaquark in the γd→ ΛnK^{+} Reaction Measured with the CLAS Spectrometer

For the first time, the reaction γd→ΛnK+ has been analyzed in order to search for the exotic pentaquark baryon Θ+(1540). The data were taken at Jefferson Laboratory, 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 γd→ΛΘ+ 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

Observation of Exclusive Deeply Virtual Compton Scattering in Polarized Electron Beam Asymmetry Measurements

We report the first results of the beam-spin asymmetry measured in the reaction ep→epγ at a beam energy of 4.25 GeV. A large asymmetry with a sinφ modulation is observed, as predicted for the interference term of deeply virtual compton scattering (DVCS) and the Bethe-Heitler process. The amplitude of this modulation is α=0.202±0.028. In leading-order and leading-twist perturbative QCD, the α is directly proportional to the imaginary part of the DVCS amplitude

Electroproduction of the Λ(1520) hyperon

The reaction ep⃗ e′K+Λ(1520) with Λ(1520)→p′K- was studied at electron beam energies of 4.05, 4.25, and 4.46 GeV, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cosθK+, φK+, Q2, and W dependencies of Λ(1520) electroproduction are presented for the kinematic region 0.

Strange-quark contributions to parity-violating asymmetries in the forward G0 electron-proton scattering experiment

We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12≤Q2≤1.0  GeV2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, Q2 dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments

Beam-recoil polarization transfer in the nucleon resonance region in the exclusive e→p→e′K+Λ→ and e→p→e′K+Σ→0 reactions at the CLAS spectrometer

Beam-recoil transferred polarizations for the exclusive e→p→e′K+Λ→,Σ→0 reactions have been measured using the Continuous Electron Beam Accelerator Facility\u27s large acceptance spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. New measurements have been completed at beam energies of 4.261 and 5.754 GeV that span a range of momentum transfer Q2 from 0.7 to 5.4 GeV2, invariant energy W from 1.6 to 2.6 GeV, and the full center-of-mass angular range of the K+ meson. These new data add to the existing CLAS K+Λ measurements at 2.567 GeV, and provide the first-ever data for the K+Σ0 channel in electroproduction. Comparisons of the data with several theoretical models are used to study the sensitivity to s-channel resonance contributions and the underlying reaction mechanism. Interpretations within two semiclassical partonic models are made to probe the underlying reaction mechanism and the ss¯ quark-pair creation dynamics