Recent results on pp → ppϕ/K+K− production and the momentum dependence of ϕ-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 sep- arated into kaon pairs arising from the decay of the φ-meson and the remainder. The measurements show that higher partial waves represent the majority of the pp → ppφ 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 φp enhancement near threshold. The non- φK + K − data can be described in terms of the combined effects of two-body final state inter- actions, using the same effective scattering parameters already determined from lower energy ANKE data. (2) The inclusive production of φ mesons on C, Cu, Ag, and Au targets has also been studied using the K + K − decay to detect the φ. The momentum de- pendence of the nuclear transparency ratio, the in-medium φ width, and the differential cross section for φ meson production at forward angles have been determined for these nuclei in the momentum range of 0.6 - 1.6 GeV/c .T here are indications of a significant momentum dependence in the values extracted for the φ width, which on average exceed the free value by about an order of mag- nitude. The results are compared with data from other experiments at slightly higher momenta.

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