Recent results on pp -> pp pi/K+ K- production and the momentum dependence of phi-meson nuclear transparency

Kaon pair production by 2.83 GeV protons has been investigated in two experiments using the ANKE magnetic spectrometer at COSY-Julich: (1) Differential and total cross sections for the pp -> ppK(+)K(-) reaction are separated into kaon pairs arising from the decay of the phi-meson and the remainder. The measurements show that higher partial waves represent the majority of the pp -> pp phi cross section at an excess energy of 76 MeV. Taken together with existing low energy ANKE data, the energy dependence of the results seem to suggest some S-wave phi p enhancement near threshold. The non-phi K+ K- data can be described in terms of the combined effects of two-body final state interactions, using the same effective scattering parameters already determined from lower energy ANKE data. (2) The inclusive production of phi mesons on C, Cu, Ag, and Au targets has also been studied using the K+ K- decay to detect the phi. The momentum dependence of the nuclear transparency ratio, the in-medium phi width, and the differential cross section for phi meson production at forward angles have been determined for these nuclei in the momentum range of 0.6 - 1.6 GeV/c. There are indications of a significant momentum dependence in the values extracted for the phi width, which on average exceed the free value by about an order of magnitude. The results are compared with data from other experiments at slightly higher momenta.