The f1(1285) meson with mass 1281.0 ± 0.8 MeV/c 2 and width 18.4 ± 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 ηπ + π − , K +K 0 π − , and K − K 0 π + 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 J P = 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 a ± 0 (980)π ∓ states, with the branching ratio Γ(a0π (noKK))/Γ(ηππ (all)) = 0.74±0.09. The branching ratios Γ(KKπ)/Γ(ηππ) = 0.216±0.033 and Γ(γρ 0 )/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.

Because of their long lifetimes, the ω and ϕ mesons are the ideal candidates for the study of possible modifications of the in-medium meson-nucleon interaction through their absorption inside the nucleus. During the E01-112 experiment at the Thomas Jefferson National Accelerator Facility, the mesons were photoproduced from 2H, C, Ti, Fe, and Pb targets. This Letter reports the first measurement of the ratio of nuclear transparencies for the e+e- channel. The ratios indicate larger in-medium widths compared with what have been reported in other reaction channels. The absorption of the ω meson is stronger than that reported by the CBELSA-TAPS experiment and cannot be explained by recent theoretical models.

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Background: Measurements of polarization observables for the reactions γ p → K + and γ p → K + 0 have been performed. This is part of a program of measurements designed to study the spectrum of baryon resonances in particular, and nonperturbative QCD in general. Purpose: The accurate measurement of several polarization observables provides tight constraints for phenomenological fits, which allow the study of strangeness in nucleon and nuclear systems. Beam-recoil observables for the γ p → K + 0 reaction have not been reported before now. Method: The measurements were carried out using linearly polarized photon beams incident on a liquid hydrogen target, and the CLAS detector at the Thomas Jefferson National Accelerator Facility. The energy range of the results is 1.71 < W < 2.19 GeV, with an angular range −0.75 < cos θ K < +0.85. Results: The observables extracted for both reactions are beam asymmetry , target asymmetry T , and the beam-recoil double polarization observables O x and O z .

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