Isospin-symmetry in $pp$ and $AA$ collisions

Abstract

The hypothesis of a violation of isospin-symmetry in pp and AA collisions is discussed. We show that the ratio of charged-to-neutral kaon cross sections, $R_K~=~\frac{σ_{K^+}+σ_{K^-}}{2σ_{K^0_S}}$, calculated within the similarity approach, including the gluon transverse momentum dependence (TMD) at low QCD scales, and using the Lund model in the form of the MC generator PYTHIA, is above 1 at energies $\sqrt{s}$ up to 20 GeV, even in the case of isospin-symmetry conservation. It decreases to 1, when the energy rises to a few TeV (ALICE data). The reason for this is related to the dynamics of kaon production. This energy behavior of $R_K$ does practically not depend on the sort of beam or target.