Influence of $\phi$ mesons on negative kaons in Ni+Ni collisions at 1.91A GeV beam energy

TL;DR

This study measures $ ext{phi}$ and negative kaons in Ni+Ni collisions at 1.91A GeV, revealing that about 22% of negative kaons originate from $ ext{phi}$ decays, impacting the understanding of meson production and spectra.

Contribution

It provides the first detailed measurement of $ ext{phi}$ mesons and their contribution to negative kaons in Ni+Ni collisions at this energy, highlighting their role in kaon spectral differences.

Findings

Approximately 22% of K$^-$ originate from $ ext{phi}$ decays.

Inverse slopes of direct kaons are up to 15 MeV larger than one-source model predictions.

$ ext{phi}$ mesons contribute significantly to negative kaon yields and spectra.

Abstract

$\phi$ and K$^-$ 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 semi-central events amounting to 51% of the total cross section. The phase space distributions, and the total yield of K$^-$, as well as the kinetic energy distribution and the total yield of $\phi$ mesons are presented. The $\phi$\K$^-$ ratio is found to be $0.44 \pm 0.07(\text{stat}) ^{+0.18}_{-0.12} (\text{syst})$, meaning that about 22% of K$^-$ mesons originate from the decays of $\phi$ 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, signalling that a considerable share of gap between the slopes of K$^+$ and K$^-$ could be explained by the contribution of $\phi$ mesons to negative kaons.