Subthreshold phi-meson production and medium effects in proton-nucleus reactions

摘要

Within the spectral function approach, we study the direct production and decay via the dikaon (dimuon) channel of phi mesons in the interactions of 2.4- and 2.7-GeV protons with light and medium target nuclei. It is shown that the K+K- (mu(+)mu(-)) invariant-mass distribution consists of the two components, which correspond to the phi decay "outside" and "inside" the target nucleus. The first (narrow) component has the free 6 width, while the second (broad) component is distorted by the nuclear matter owing to resonance-nucleon scattering and a possible in-medium modification of the kaons and rho meson at finite baryon density. The relative strength of the "inside" and "outside" components is analyzed in different scenarios for the phi 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 phi width by a factor of about 2 if the total phi in-medium width is used and the respective cutoff for the phi three-momentum is applied, whereas the resulting dikaon invariant-mass distribution has an insignificant sensitivity to the phi in-medium properties owing 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 of 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.