Subthreshold φ-meson production and medium effects in proton-nucleus reactions
Institute for Nuclear Research, Russian Academy of Sciences, 117312, Moscow, Russia
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Accepted: 3 November 2004
Published online: 5 January 2005
Within the spectral function approach we study the direct production and decay via the dikaon (dimuon) channel of φ-mesons in the interactions of 2.4 and 2.7GeV protons with light and medium target nuclei. It is shown that the K + K - ( μ+μ-) invariant-mass distribution consists of the two components which correspond to the φ decay “outside” and “inside” the target nucleus. The first (narrow) component has the free φ width, while the second (broad) component is distorted by the nuclear matter due to resonance-nucleon scattering and a possible in-medium modification of the kaons and ρ-meson at finite baryon density. The relative strength of the “inside” and “outside” components is analyzed in different scenarios for the φ width and momentum cut. It is demonstrated that the width of the resulting dimuon invariant-mass distribution on medium nuclei is larger than the free φ width by a factor of about two if the total φ in-medium width is used and the respective cutoff for the φ three-momentum is applied, whereas the resulting dikaon invariant-mass distribution has an insignificant sensitivity to the φ in-medium properties due to the strong absorption of the K- in the surrounding nuclear matter. On the other hand, because of the distortion of the K+ and K- on their way out the target nucleus mainly due to the hadronic kaon potentials, the latter distribution is broadened and shifted to higher invariant masses, which means that the measurement of such broadening would give additional evidence for the modification of the kaon and antikaon properties in the nuclear medium.
PACS: 25.40.-h Nucleon-induced reactions –
© Società Italiana di Fisica and Springer-Verlag, 2005