Near-threshold $ω$ and $ϕ$ meson productions in $pp$ collisions

Abstract

Using a relativistic effective Lagrangian at the hadronic level, near-threshold $ω$ and $ϕ$ meson productions in proton proton ($pp$) collisions, $p p \to p p ω/ϕ$, 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 $ω$ and $ϕ$ angular distribution data are used to constrain further the model parameters. For the $p p \to p p ω$ 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 $π^- p \to ωn$ 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 $p p \to p p ϕ$ 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 $ϕNN$ coupling constants. Further measurements of the energy dependence of the total cross section near threshold energies should help to constrain better the $ϕNN$ coupling constant.