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Register a new userDynamical model of $phi$ meson photoproduction on the nucleon and $^4He$
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We investigate $phi$ meson photoproduction on the nucleon and the uclide[4]{He} targets within a dynamical model approach based on a Hamiltonian which describes the production mechanisms by the Pomeron-exchange, meson-exchanges, $phi$ radiations, and nucleon resonance excitations mechanisms. The final $phi N$ interactions are included being described by the gluon-exchange, direct $phi N$ couplings, and the box-diagrams arising from the couplings with $pi N$, $rho N$, $KLambda$, and $KSigma$ channels. The parameters of the Hamiltonian are determined by the experimental data of $gamma p to phi p$ from the CLAS Collaboration. The resulting Hamiltonian is then used to predict the coherent $phi$-meson production on the uclide[4]{He} targets by using the distorted-wave impulse approximation. For the proton target, the final $phi N$ rescattering effects, as required by the unitarity condition, are found to be very weak, which supports the earlier calculations in the literature. For the uclide[4]{He} targets, the predicted differential cross sections are in good agreement with the data obtained by the LEPS Collaboration. The role of each mechanism in this reaction is discussed and predictions for a wide range of scattering angles are presented, which can be tested in future experiments.
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We compute dilepton invariant mass spectra from the decays of rho mesons produced by photon reactions off nuclei. Our calculations employ a realistic model for the rho photoproduction amplitude on the nucleon which provides fair agreement with measured cross sections. Medium effects are implemented via an earlier constructed rho propagator based on hadronic many-body theory. At incoming photon energies of 1.5 -3 GeV as used by the CLAS experiment at JLAB, the average density probed for iron targets is estimated at about half saturation density. At the pertinent rho-meson 3-momenta the predicted medium effects on the rho propagator are rather moderate. The resulting dilepton spectra approximately agree with recent CLAS data.
We study $eta$ photoproduction off the deuteron ($gamma dtoeta pn$) at a special kinematics: $sim 0.94$ GeV of the photon beam energy and $sim 0^circ$ of the scattering angle of the proton. This kinematics is ideal to extract the low-energy $eta$-nucleon scattering parameters such as $a_{eta N}$ (scattering length) and $r_{eta N}$ (effective range) because the $eta$-nucleon elastic scattering is significantly enhanced. We show that if a ratio $R$, the $gamma dtoeta pn$ cross section divided by the $gamma ptoeta p$ cross section convoluted with the proton momentum distribution in the deuteron, is measured with 5% error, ${rm Re}[a_{eta N}]$ (${rm Re}[r_{eta N}]$) can be determined at the precision of $simpm$0.1 fm ($simpm$0.5 fm), significantly narrowing down the currently estimated range of the parameters. The measurement is ongoing at the Research Center for Electron Photon Science (ELPH), Tohoku University.
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