Analysis of data for γp → f1(1285)p photoproduction

The photoproduction of the f1(1285)meson off the proton target is investigated within an effective Lagrangian approach.The t-channelρ-andω-exchange diagrams,u-channel nucleon-exchange diagram,generalized contact term,and s-channel pole diagrams of the nucleon and a minimal number of nucleon resonances are taken into account in constructing the reaction amplitudes to describe the experimental data.Three different models,that is,the Feynman,Regge,and interpolated Regge models,are employed,where the t-channel reaction amplitudes are constructed in Feynman,Regge,and interpolated Regge types,respectively.The results show that neither the Feynman model with two nucleon resonances nor the interpolated Regge model with one nucleon resonance can satisfactorily reproduce the available data forγp→f1(1285)p.Nevertheless,in the Regge model,when any one of the N(1990)7/2^(+),N(2000)5/2^(+),N(2040)3/2^(+),N(2060)5/2^(-),N(2100)1/2^(+),N(2120)3/2^(-),N(2190)7/2^(-),N(2300)1/2^(+),and N(2570)5/2^(-)resonances is considered,the data can be well described.The resulting resonance parameters are consistent with those advocated in the Particle Data Group(PDG)review.Further analysis shows that,in the high-energy region,the peaks of γp→f1(1285)p differential cross sections at forward angles are dominated by the contributions from t-channelρ-andω-exchange diagrams,while in low-energy region,the s-channel pole diagrams of resonances also provide significant contributions to theγp→f1(1285)p cross sections.

Photoproductionγp→K^(+)Λ(1690)in an effective Lagrangian approach

A gauge-invariant model is constructed for theγp→K^(+)Λ(1690)reaction within a tree-level effective Lagrangian approach to understand the underlying production mechanisms and study the resonance contributions in this reaction.In addition to the t-channel K and K^(∗)exchanges,s-channel nucleon exchange,and interaction current,the s-channel nucleon resonance exchanges are included in constructing the reaction amplitudes to describe the data.It is found that the contributions from the s-channel N(2570)5/2^(−)exchange are required to describe the most recently measured total cross-section data forγp→K^(+)Λ(1690)from the CLAS Collaboration.Further analysis indicates that the interaction current dominates the γ p→K^(+)Λ(1690)reaction near the threshold as a result of gauge invariance.The t-channel K exchange contributes significantly,while the contributions from the t-channel K^(∗)exchange and s-channel nucleon exchange are ultimately negligible.The contributions from the s-channel N(2570)5/2^(−)exchange are found to be responsible for the bump structure shown in the CLAS total cross-section data above the center-of-mass energy W≈2.7 GeV.The predictions of the differential cross sections forγp→K^(+)Λ(1690)are presented and discussed,which can provide theoretical guidance for future experiments.