Mineeva, Taisiya

Despite decades of studies of the photoproduction of hyperons, both their production mechanisms and their spectra of excited states are still largely unknown. While the parity-violating weak decay of hyperons offers a means of measuring their polarization, which could help discern their production mechanisms and identify their excitation spectra, no such study has been possible for doubly strange baryons in photoproduction, due to low production cross sections. However, by making use of the reaction , we have measured, for the first time, the induced polarization, P, and the transferred polarization from circularly polarized real photons, characterized by and , to recoiling s. The data were obtained using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab for photon energies from just over threshold (2.4 GeV) to 5.45 GeV. These first-time measurements are compared, and are shown to broadly agree, with model predictions in which cascade photoproduction proceeds through the decay of intermediate hyperon resonances that are produced via relativistic meson exchange, offering a new step forward in the understanding of the production and polarization of doubly-strange baryons.

We present precision measurements of the target and beam-target spin asymmetries from neutral pion electroproduction in deep-inelastic scattering (DIS) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. We scattered 6-GeV, longitudinally polarized electrons off longitudinally polarized protons in a cryogenic 14NH3 target, and extracted double and single target spin asymmetries for ep → e π0 X in multidimensional bins in four-momentum transfer (1.0 < Q 2 < 3.2 GeV2), Bjorken-x (0.12 < x < 0.48), hadron energy fraction (0.4 < z < 0.7), transverse pion momentum (0 < PT < 1.0 GeV), and azimuthal angle φh between the lepton scattering and hadron production planes. We extracted asymmetries as a function of both x and PT , which provide access to transverse-momentum distributions of longitudinally polarized quarks. The double spin asymmetries depend weakly on PT . The sin 2φh moments are zero within uncertainties, which is consistent with the expected suppression of the Collins fragmentation function. The observed sinφh moments suggest that quark gluon correlations are significant at large x.

We report a measurement of a beam–target double-polarisation observable (E) for the γn(p) → K +−(p) reaction. The data were obtained impinging the circularly-polarised energy-tagged photon beam of Hall B at Jefferson Lab on a longitudinally-polarised frozen-spin hydrogen deuteride (HD) nuclear target. The E observable for an effective neutron target was determined for centre-of-mass energies 1.70 ≤ W ≤ 2.30 GeV, with reaction products detected over a wide angular acceptance by the CLAS spectrometer. These new double-polarisation data give unique constraints on the strange decays of excited neutron states. Inclusion of the new data within the Bonn-Gatchina theoretical model results in significant changes for the extracted photocouplings of a number of established nucleon resonances. Possible improvements in the PWA description of the experimental data with additional “missing” resonance states, including the N(2120)3/2− resonance, are also quantified.

The photoproduction of ω mesons off the proton has been studied in the reaction γp → p ω using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the target asymmetry T has been measured in photoproduction from the decay ω → π+π−π0, using a transversely polarized target with energies ranging from just above the reaction threshold up to 2.8 GeV. Significant nonzero values are observed for these asymmetries, reaching about 30–40% in the third-resonance region. New measurements for the photon-beam asymmetry are also presented, which agree well with previous CLAS results and extend the world database up to 2.1 GeV. These data and additional ω photoproduction observables from CLAS were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from s-channel resonance production were found in addition to t-channel exchange processes.