55 research outputs found

    First measurement of the helicity asymmetry E in eta photoproduction on the proton

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    Results are presented for the first measurement of the double-polarization helicity asymmetry E for the η\eta photoproduction reaction γpηp\gamma p \rightarrow \eta p. Data were obtained using the FROzen Spin Target (FROST) with the CLAS spectrometer in Hall B at Jefferson Lab, covering a range of center-of-mass energy W from threshold to 2.15 GeV and a large range in center-of-mass polar angle. As an initial application of these data, the results have been incorporated into the J\"ulich model to examine the case for the existence of a narrow NN^* resonance between 1.66 and 1.70 GeV. The addition of these data to the world database results in marked changes in the predictions for the E observable using that model. Further comparison with several theoretical approaches indicates these data will significantly enhance our understanding of nucleon resonances

    First measurement of the polarization observable E in the p→(γ→,π<sup>+</sup>)n reaction up to 2.25 GeV

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    First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction γpπ+n\vec \gamma \vec p \to \pi^+n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37 GeV. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility. These polarization data agree fairly well with previous partial-wave analyses at low photon energies. Over much of the covered energy range, however, significant deviations are observed, particularly in the high-energy region where high-L multipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn-Gatchina, J\"ulich, and SAID groups.Comment: 6 pages, 3 figure

    Semi-inclusive pi(0) target and beam-target asymmetries from 6 GeV electron scattering with CLAS

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    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 14^{14}NH3_3 target, and extracted double and single target spin asymmetries for epeπ0Xep\rightarrow e^\prime\pi^0X in multidimensional bins in four-momentum transfer (1.0<Q2<3.21.0<Q^2<3.2 GeV2^2), Bjorken-xx (0.12<x<0.480.12<x<0.48), hadron energy fraction (0.4<z<0.70.4<z<0.7), transverse pion momentum (0<PT<1.00<P_T<1.0 GeV), and azimuthal angle ϕh\phi_h between the lepton scattering and hadron production planes. We extracted asymmetries as a function of both xx and PTP_T, which provide access to transverse-momentum distributions of longitudinally polarized quarks. The double spin asymmetries depend weakly on PTP_T. The sin2ϕh\sin 2\phi_h moments are zero within uncertainties, which is consistent with the expected suppression of the Collins fragmentation function. The observed sinϕh\sin\phi_h moments suggest that quark gluon correlations are significant at large xx.Comment: 18 preprint pages, 3 figure
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