CLAS

The $f_1(1285)$ meson with mass $1281.0 \pm 0.8$ MeV/$c^2$ and width $18.4 \pm 1.4$ MeV (FWHM) was measured for the first time in photoproduction from a proton target using CLAS at Jefferson Lab. Differential cross sections were obtained via the $\eta\pi^{+}\pi^{-}$, $K^+\bar{K}^0\pi^-$, and $K^-K^0\pi^+$ decay channels from threshold up to a center-of-mass energy of 2.8 GeV and are compared to model predictions. An amplitude analysis of the $\eta\pi^{+}\pi^{-}$ final-state Dalitz distribution is consistent with identification as the axial-vector $J^P=1^+$ $f_1(1285)$, rather than the pseudoscalar $0^-$ $\eta(1295)$. The production mechanism is most consistent with $s$-channel decay of a high-mass $N^*$ state, and not with $t$-channel meson exchange. Decays of the $f_1(1285)$ to $\eta \pi \pi$ are clearly dominated the intermediate states $a_0^\pm(980)\pi^\mp$. The branching ratios $\Gamma(a_0\pi (no \bar{K} K)) / \Gamma(\eta\pi\pi (all))$, $\Gamma(K \bar{K} \pi)/\Gamma(\eta\pi\pi) $ and $\Gamma(\gamma\rho^0)/\Gamma(\eta\pi\pi)$ were obtained and will be compared to world averages.