14 research outputs found

    Effective Lagrangian Approach to the Theory of Eta Photoproduction in the N∗(1535)N^{*}(1535) Region

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    We investigate eta photoproduction in the N∗(1535)N^{*}(1535) resonance region within the effective Lagrangian approach (ELA), wherein leading contributions to the amplitude at the tree level are taken into account. These include the nucleon Born terms and the leading tt-channel vector meson exchanges as the non-resonant pieces. In addition, we consider five resonance contributions in the ss- and uu- channel; besides the dominant N∗(1535)N^{*}(1535), these are: N∗(1440),N∗(1520),N∗(1650)N^{*}(1440),N^{*}(1520),N^{*}(1650) and N∗(1710)N^{*}(1710). The amplitudes for the π∘\pi^\circ and the η\eta photoproduction near threshold have significant differences, even as they share common contributions, such as those of the nucleon Born terms. Among these differences, the contribution to the η\eta photoproduction of the ss-channel excitation of the N∗(1535)N^{*}(1535) is the most significant. We find the off-shell properties of the spin-3/2 resonances to be important in determining the background contributions. Fitting our effective amplitude to the available data base allows us to extract the quantity χΓηA1/2/ΓT\sqrt{\chi \Gamma_\eta} A_{1/2}/\Gamma_T, characteristic of the photoexcitation of the N∗(1535)N^{*}(1535) resonance and its decay into the η\eta-nucleon channel, of interest to precise tests of hadron models. At the photon point, we determine it to be (2.2±0.2)×10−1GeV−1(2.2\pm 0.2)\times 10^{-1} GeV^{-1} from the old data base, and (2.2±0.1)×10−1GeV−1(2.2\pm 0.1) \times 10^{-1} GeV^{-1} from a combination of old data base and new Bates data. We obtain the helicity amplitude for N∗(1535)→γpN^{*}(1535)\rightarrow \gamma p to be A1/2=(97±7)×10−3GeV−1/2A_{1/2}=(97\pm 7)\times 10^{-3} GeV^{-1/2} from the old data base, and A1/2=(97±6)×10−3GeV−1/2A_{1/2}=(97\pm 6)\times 10^{-3} GeV^{-1/2} from the combination of the old data base and new Bates data, compared with the results of the analysis of pion photoproduction yielding 74±1174\pm 11, in the same units.Comment: 43 pages, RevTeX, 9 figures available upon request, to appear in Phys. Rev.
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