406 research outputs found

    Comment on the narrow structure reported by Amaryan et al

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    The CLAS Collaboration provides a comment on the physics interpretation of the results presented in a paper published by M. Amaryan et al. regarding the possible observation of a narrow structure in the mass spectrum of a photoproduction experiment.Comment: to be published in Physical Review

    Beam-target helicity asymmetry for γ→n→→π−p in the N*resonance region

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    We report the first beam-target double-polarization asymmetries in the Îł ĂŸ nĂ°pÞ → π− ĂŸ pĂ°pÞ reaction spanning the nucleon resonance region from invariant mass W ÂŒ 1500 to 2300 MeV. Circularly polarized photons and longitudinally polarized deuterons in solid hydrogen deuteride (HD) have been used with the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The exclusive final state has been extracted using three very different analyses that show excellent agreement, and these have been used to deduce the E polarization observable for an effective neutron target. These results have been incorporated into new partial wave analyses and have led to significant revisions for several ÎłnN* resonance photocouplings

    Measurement of the Polarized Structure Function σLTâ€Č\sigma_{LT^\prime} for p(e⃗,eâ€Čπ+)np(\vec{e},e'\pi^+)n in the Δ(1232)\Delta(1232) Resonance Region

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    The polarized longitudinal-transverse structure function σLTâ€Č\sigma_{LT^\prime} has been measured using the p(e⃗,eâ€Čπ+)np(\vec e,e'\pi^+)n reaction in the Δ(1232)\Delta(1232) resonance region at Q2=0.40Q^2=0.40 and 0.65 GeV2^2. No previous σLTâ€Č\sigma_{LT^\prime} data exist for this reaction channel. The kinematically complete experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) using longitudinally polarized electrons at an energy of 1.515 GeV. A partial wave analysis of the data shows generally better agreement with recent phenomenological models of pion electroproduction compared to the previously measured π0p\pi^0 p channel. A fit to both π0p\pi^0 p and π+n\pi^+ n channels using a unitary isobar model suggests the unitarized Born terms provide a consistent description of the non-resonant background. The tt-channel pion pole term is important in the π0p\pi^0 p channel through a rescattering correction, which could be model-dependent.Comment: 6 pages, LaTex, 5 eps figures: Submitted to PRC/Brief Reports v2: Updated referenc

    Search for Θ+(1540)\Theta^+(1540) pentaquark in high statistics measurement of γp→Kˉ0K+n\gamma p \to \bar K^0 K^+ n at CLAS

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    The exclusive reaction γp→Kˉ0K+n\gamma p \to \bar K^0 K^+ n was studied in the photon energy range between 1.6-3.8 GeV searching for evidence of the exotic baryon Θ+(1540)→nK+\Theta^+(1540)\to nK^+. The decay to nK+nK^+ requires the assignment of strangeness S=+1S=+1 to any observed resonance. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility corresponding to an integrated luminosity of 70 pb−1pb^{-1}. No evidence for the Θ+\Theta^+ pentaquark was found. Upper limits were set on the production cross section as function of center-of-mass angle and nK+nK^+ mass. The 95% CL upper limit on the total cross section for a narrow resonance at 1540 MeV was found to be 0.8 nb.Comment: Submitted to Physical Review Letter

    Q^2 Dependence of the S_{11}(1535) Photocoupling and Evidence for a P-wave resonance in eta electroproduction

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    New cross sections for the reaction ep→eâ€Čηpep \to e'\eta p are reported for total center of mass energy WW=1.5--2.3 GeV and invariant squared momentum transfer Q2Q^2=0.13--3.3 GeV2^2. This large kinematic range allows extraction of new information about response functions, photocouplings, and ηN\eta N coupling strengths of baryon resonances. A sharp structure is seen at W∌W\sim 1.7 GeV. The shape of the differential cross section is indicative of the presence of a PP-wave resonance that persists to high Q2Q^2. Improved values are derived for the photon coupling amplitude for the S11S_{11}(1535) resonance. The new data greatly expands the Q2Q^2 range covered and an interpretation of all data with a consistent parameterization is provided.Comment: 31 pages, 9 figure

    Measurement of Deeply Virtual Compton Scattering with a Polarized Proton Target

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    The longitudinal target-spin asymmetry A_UL for the exclusive electroproduction of high energy photons was measured for the first time in p(e,e'p\gamma). The data have been accumulated at Jefferson Lab with the CLAS spectrometer using 5.7 GeV electrons and a longitudinally polarized NH_3 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(phi) moment is 0.252 +/- 0.042(stat) +/- 0.020(sys). 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-tilde.Comment: Modified text slightly, added reference

    First measurement of coherent ϕ\phi-meson photoproduction on deuteron at low energies

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    The cross section and decay angular distributions for the coherent \phi meson photoproduction on the deuteron have been measured for the first time up to a squared four-momentum transfer t =(p_{\gamma}-p_{\phi})^2 =-2 GeV^2/c^2, 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 \phi-N cross section \sigma_{\phi N} at about 10 mb. If vector meson dominance is violated, a larger \sigma_{\phi N} is possible by introducing larger t-slope for the \phi N \to \phi N process than that for the \gamma N \to \phi N process. The decay angular distributions of the \phi are consistent with helicity conservation.Comment: 6 page

    Target and beam-target spin asymmetries in exclusive pion electroproduction for Q2>1GeV2 . I. ep→eπ+n

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    Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive π + electroproduction reaction Îł ∗ p → n π + . The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic range covered is 1.1 < W < 3 GeV and 1 < Q 2 < 6 GeV 2 . Results were obtained for about 6000 bins in W ,   Q 2 ,   cos ( Ξ ∗ ) , and ϕ ∗ . Except at forward angles, very large target-spin asymmetries are observed over the entire W region. Reasonable agreement is found with phenomenological fits to previous data for W < 1.6 GeV, but very large differences are seen at higher values of W . A generalized parton distributions (GPD)-based model is in poor agreement with the data. When combined with cross-sectional measurements, the present results provide powerful constraints on nucleon resonance amplitudes at moderate and large values of Q 2 , for resonances with masses as high as 2.4 GeV
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