Differential cross sections for gammap-->etap have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction ...using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W=1.75 GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass approximately 1.8 GeV couples to the etaN channel.
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The first measurements of the transferred polarization for the exclusive {rvec e}p {yields} e{prime}K{sup +}{rvec {Lambda}} reaction have been performed in Hall B at the Thomas Jefferson National ...Accelerator Facility using the CLAS spectrometer. A 2.567 GeV electron beam was used to measure the hyperon polarization over a range of Q{sup 2} from 0.3 to 1.5 (GeV/c){sup 2}, W from 1.6 to 2.15 GeV, and over the full center-of-mass angular range of the K{sup +} meson. Comparison with predictions of hadrodynamic models indicates strong sensitivity to the underlying resonance contributions. A non-relativistic quark model interpretation of our data suggests that the s{bar s} quark pair is produced with spins predominantly anti-aligned. Implications for the validity of the widely used {sup 3}P{sub o} quark-pair creation operator are discussed.
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We investigate the transition from the nucleon-meson to the quark-gluon description of the strong interaction using the photon energy dependence of the d(gamma,p)n differential cross section for ...photon energies above 0.5 GeV and center-of-mass proton angles between 30 degrees and 150 degrees. A possible signature for this transition is the onset of cross-section s(-11) scaling with the total energy squared, s, at some proton transverse momentum P(T). The results show that the scaling has been reached for proton transverse momentum above about 1.1 GeV/c. This may indicate that the quark-gluon regime is reached above this momentum.
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The differential cross section, dsigma/dt, for omega meson exclusive photoproduction on the proton above the resonance region (2.6<W<2.9 GeV) was measured up to a momentum transfer -t=5 GeV2 using ...the CLAS detector at Jefferson Laboratory. The omega channel was identified by detecting a proton and pi(+) in the final state and using the missing mass technique. While the low momentum transfer region shows the typical diffractive pattern expected from Pomeron and Reggeon exchange, at large -t the differential cross section has a flat behavior. This feature can be explained by introducing quark interchange processes in addition to the QCD-inspired two-gluon exchange.
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We report on the first measurement of exclusive {xi}{sup -}(1321) hyperon photoproduction in {gamma}p{yields}K{sup +}K{sup +}{xi}{sup -} for 3.2<E{sub {gamma}}<3.9 GeV. The final state is identified ...by the missing mass in p({gamma},K{sup +}K{sup +})X measured with the CLAS detector at Jefferson Laboratory. We have detected a significant number of the ground state {xi}{sup -}(1321)(1/2){sup +} and have estimated the total cross section for its production. We also have strong evidence for the first excited state {xi}{sup -}(1530)(3/2){sup +}. Photoproduction provides a copious source of {xi}'s. We discuss the possibilities of a search for the recently proposed {xi}{sub 5}{sup -} and {xi}{sub 5}{sup +} pentaquarks.
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The differential cross section, d sigma/dt, for rho(0) meson photoproduction on the proton above the resonance region was measured up to a momentum transfer -t = 5 GeV2 using the CLAS detector at the ...Thomas Jefferson National Accelerator Facility. The rho(0) channel was extracted from the measured two charged-pion cross sections by fitting the pi(+)pi(-) and p pi(+) invariant masses. The low momentum transfer region shows the typical diffractive pattern expected from Reggeon exchange. The flatter behavior at large -t cannot be explained solely in terms of QCD-inspired two-gluon exchange models. The data indicate that other processes, like quark interchange, are important to fully describe rho photoproduction.
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