Photoproduction of the f1(1285) meson

The f1(1285) meson with mass 1281.0±0.8 MeV/c2 and width 18.4±1.4 MeV (full width at half maximum) was measured for the first time in photoproduction from a proton target using CLAS at Jefferson Lab. Differential cross sections were obtained via the ηπ+π-,K+K̄0π-, and K-K0π+ decay channels from threshold up to a center-of-mass energy of 2.8 GeV. The mass, width, and an amplitude analysis of the ηπ+π- final-state Dalitz distribution are consistent with the axial-vector JP=1+ f1(1285) identity, rather than the pseudoscalar 0- η(1295). The production mechanism is more consistent with s-channel decay of a high-mass N∗ state and not with t-channel meson exchange. Decays to ηππ go dominantly via the intermediate a0±(980)π states, with the branching ratio Γ[a0π(noK̄K)]/Γ[ηππ(all)]=0.74±0.09. The branching ratios Γ(KK̄π)/Γ(ηππ)=0.216±0.033 and Γ(γρ0)/Γ(ηππ)=0.047±0.018 were also obtained. The first is in agreement with previous data for the f1(1285), while the latter is lower than the world average.