Influence of φ mesons on negative kaons in Ni + Ni collisions at 1.91A GeV beam energy INFLUENCE of φ MESONS on NEGATIVE KAONS in ⋯ K. PIASECKI et al.

$\\ensuremath{\\phi}$ and ${\\mathrm{K}}^{\\ensuremath{-}}$ mesons from Ni+Ni collisions at the beam energy of $1.91A$ GeV have been measured by the FOPI spectrometer, with a trigger selecting central and semicentral events amounting to 52% of the total cross section. The phase-space distributions, and the total yield of ${\\mathrm{K}}^{\\ensuremath{-}}$, as well as the kinetic energy distribution and the total yield of $\\ensuremath{\\phi}$ mesons are presented. The $\\ensuremath{\\phi}/$ ${\\mathrm{K}}^{\\ensuremath{-}}$ ratio is found to be $0.44\\ifmmode\\pm\\else\\textpm\\fi{}0.07{(\\text{stat})}_{\\ensuremath{-}0.10}^{+0.16}(\\text{syst})$, meaning that about 22% of ${\\mathrm{K}}^{\\ensuremath{-}}$ mesons originate from the decays of $\\ensuremath{\\phi}$ mesons, occurring mostly in vacuum. The inverse slopes of direct kaons are up to about 15 MeV larger than the ones extracted within the one-source model, signaling that a considerable share of gap between the slopes of ${\\mathrm{K}}^{+}$ and ${\\mathrm{K}}^{\\ensuremath{-}}$ could be explained by the contribution of $\\ensuremath{\\phi}$ mesons to negative kaons.