K + production in the reaction 58Ni+ 58Ni at incident energies from 1 to 2 A GeV

Semi-inclusive triple differential multiplicity distributions of positively charged kaons have been measured over a wide range in rapidity and transverse mass for central collisions of ⁵⁸Ni with ⁵⁸Ni nuclei. The transverse mass ( m_t) spectra have been studied as a function of rapidity at a beam energy 1.93 AGeV. The m_t distributions of K ⁺ mesons are well described by a single Boltzmann-type function. The spectral slopes are similar to that of the protons indicating that rescattering plays a significant role in the propagation of the kaon. Multiplicity densities have been obtained as a function of rapidity by extrapolating the Boltzmann-type fits to the measured distributions over the remaining phase space. The total K ⁺ meson yield has been determined at beam energies of 1.06, 1.45, and 1.93 A GeV, and is presented in comparison to existing data. The low total yield indicates that the K ⁺ meson can not be explained within a hadro-chemical equilibrium scenario, therefore indicating that the yield does remain sensitive to effects related to its production processes such as the equation of state of nuclear matter and/or modifications to the K ⁺ dispersion relation.