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Register a new userNear-threshold $omega$ and $phi$ meson productions in $pp$ collisions
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Using a relativistic effective Lagrangian at the hadronic level, near-threshold $omega$ and $phi$ meson productions in proton proton ($pp$) collisions, $p p to p p omega/phi$, are studied within the distorted wave Born approximation. Both initial and final state $pp$ interactions are included. In addition to total cross section data, both $omega$ and $phi$ angular distribution data are used to constrain further the model parameters. For the $p p to p p omega$ reaction we consider two different possibilities: with and without the inclusion of nucleon resonances. The nucleon resonances are included in a way to be consistent with the $pi^- p to omega n$ reaction. It is shown that the inclusion of nucleon resonances can describe the data better overall than without their inclusion. However, the SATURNE data in the range of excess energies $Q < 31$ MeV are still underestimated by about a factor of two. As for the $p p to p p phi$ reaction it is found that the presently limited available data from DISTO can be reproduced by four sets of values for the vector and tensor $phi NN$ coupling constants. Further measurements of the energy dependence of the total cross section near threshold energies should help to constrain better the $phi NN$ coupling constant.
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We present results for the $p p to p p omega$ reaction studied by considering two different scenarios: with and without the inclusion of nucleon resonance excitations. The recently measured angular distribution by the COSY-TOF Collaboration at an excess energy of $Q = 173$ MeV and the energy dependence of the total cross section data for $pi^- p to omega n$ are used to calibrate the model parameters. The inclusion of nucleon resonances improves the theoretical prediction for the energy dependence of the total cross section in $pp to ppomega$ at excess energies $Q < 31$ MeV. However, it still underestimates the data by about a factor of two, and remains a problem in understanding the reaction mechanism.
We investigate the reactions p n -> d omega and p n -> d phi close to the corresponding thresholds. The S-wave amplitudes are calculated within the framework of the two-step model which is described by a triangle graph with pi, rho and omega mesons in the intermediate state. The cross sections of the reactions p n -> d omega and p n -> d phi are predicted to be significantly larger than the cross sections of the corresponding reactions p p -> p p omega and p p -> p p phi at the same values of the c.m. excess energy Q. The ratio of the yields of phi to omega is found to be (30 +/- 7) x 10^-3.
The total cross section for omega production in the pp -> pp omega reaction has been measured at five c.m. excess energies from 3.8 to 30 MeV. The energy dependence is easily understood in terms of a strong proton-proton final state interaction combined with a smearing over the width of the state. The ratio of near-threshold phi and omega production is consistent with the predictions of a one-pion-exchange model and the degree of violation of the OZI rule is similar to that found in the pi-p -> n omega/phi reactions.
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.
An experimental study of $omega$ photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The $gamma ptoomega p$ differential cross sections are measured from threshold to the incident-photon energy $E_gamma=1.40$ GeV ($W=1.87$ GeV for the center-of-mass energy) with 15-MeV binning in $E_gamma$ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the $omega N$ scattering length $alpha_{omega p}$ is provided.
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