Recent results on pp → ppϕ/K⁺K⁻ production and the momentum dependence of ϕ-meson nuclear transparency

¹ Institut für Kernphysik and Jülich Centre for Hadron Physics, Forschungszentrum Jülich, D-52425 Jülich, Germany
² Institut für Kern- und Hadronenphysik, Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden, Germany
³ Institute for Theoretical and Experimental Physics, RU-117218 Moscow, Russia
⁴ Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
⁵ Departament d'Estructura i Constituents de la Matèrria and Institut de Ciències del Cosmos, Universitat de Barcelona, E-08028 Barcelona, Spain
⁶ Institute for Nuclear Research, Russian Academy of Sciences, RU-117312 Moscow, Russia
⁷ Departamento de F´?sica, Universidad de Murcia, E-30071 Murcia, Spain
⁸ Institut f¨ur Theoretische Physik, TU Dresden, D-01062 Dresden, Germany
⁹ Physics and Astronomy Department, UCL, London WC1E 6BT, United Kingdom
¹⁰ Department of Physics and Triangle Universities Nuclear Laboratory, Duke University, Durham, NC 27708, USA

^a e-mail: m.hartmann@fz-juelich.de

Abstract

Kaon pair production by 2.83 GeV protons has been investigated in two experiments using the ANKE magnetic spectrometer at COSY-Jülich:

(1) Differential and total cross sections for the pp → ppK⁺ K⁻ reaction are separated 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-ϕ 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 ϕ mesons on C, Cu, Ag, and Au targets has also been studied using the K⁺K⁻ decay to detect the ϕ. The momentum dependence 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. There 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 magnitude. The results are compared with data from other experiments at slightly higher momenta.