On the near-threshold peak structure in the differential cross section of ϕ-meson photoproduction: indication of a missing resonance with non-negligible strangeness content

Abstract

The details of the analysis of the near-threshold bump structure in the forward differential cross section of the ϕ-meson photoproduction to determine whether it is a signature of a resonance are presented. The analysis is carried out in an effective Lagrangian approach which includes Pomeron and (π,η) 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 (SDME) as recently measured, instead of the phi-meson decay angular distributions which depend only on six SDMEs 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 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 ω-meson photoproduction and theoretical model can be considerably reduced. We argue that the large value of x_{OZI} indicates that the postulated resonance contains non-negligible amount of strangeness content.