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High-statistics differential cross sections for the reactions γp → pη and γp → pη have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass energies from near threshold up to 2.84 GeV. The η results are the most precise to date and provide the largest energy and angular coverage. The η measurements extend the energy range of the world's large-angle results by approximately 300 MeV. These new data, in particular the η measurements, are likely to help constrain the analyses being performed to search for new baryon resonance states.

High-statistics cross sections and recoil polarizations for the reactions ␥ + p → K + + ⌳ and ␥ + p → K + + ⌺ 0 have been measured at CLAS for center-of-mass energies between 1.6 and 2.3 GeV. In the K + ⌳ channel we confirm a resonance-like structure near W = 1.9 GeV at backward kaon angles. Our data show more complex sand u-channel behavior than previously seen, since structure is also present at forward angles, but not at central angles. The position and width change with angle, indicating that more than one resonance is playing a role. Large positive ⌳ polarization at backward angles, which is also energy dependent, is consistent with sizable s-or u-channel contributions. Presently available model calculations cannot explain these aspects of the data.

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.