科研之友
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摘要
The details of the analysis of the near-threshold bump structure in the forward differential cross section of the phi-meson photoproduction to determine whether it is a signature of a resonance, together with more extensive results, are presented. The analysis is carried out in an effective Lagrangian approach which includes Pomeron and (pi, eta) exchanges in the t channel and contributions from the s- and u-channel excitations of a postulated nucleon resonance. In addition to the differential cross sections, we use the nine spin-density matrix elements as recently measured, instead of the phi-meson decay angular distributions which depend only on six spin-density matrix elements as was done before, to constrain the resonance parameters. We conclude that indeed the nonmonotonic behavior, along with the other experimental data as reported by LEPS, can only be explained with an assumption of the excitation of a resonance of spin 3/2, as previously reported. However, both parities of (+/-) can account for the data equally well with almost identical mass of 2.08 +/- 0.04 GeV and width of 0.501 +/- 0.117 and 0.570 +/- 0.159 for 3/2(+) and 3/2(-), respectively. The ratio of the helicity amplitudes A(1/2)/A(3/2) calculated from the resulting coupling constants differs in sign from that of the known D-13(2080). More experimental data on single and double polarization observables are needed to resolve the parity. We further find that with an assumption of large values of the OZI-evading parameters x(OZI) = 12 for J(P) = 3/2(-) and x(OZI) = 9 for J(P) = 3/2(+), the discrepancy between the recent experimental data on omega-meson photoproduction and the theoretical model can be considerably reduced. We argue that the large value of x(OZI) indicates that the postulated resonance contains a non-negligible amount of strangeness content.
- 出版日期2012-7-5
