Enhanced production of charged over neutral kaons in Ar+Sc collisions measured by NA61/SHINE at CERN SPS

TL;DR

This paper reports that charged kaons are produced significantly more than neutral kaons in Ar+Sc collisions at CERN SPS, challenging existing hadron production models that include isospin symmetry breaking effects.

Contribution

It provides the first measurement of charged versus neutral kaon production in Ar+Sc collisions at 11.9 GeV, revealing an unexpected enhancement of charged kaons.

Findings

Charged kaon production exceeds neutral kaon production by 18.4%.

Current models cannot explain the observed isospin asymmetry.

Results suggest new physics or mechanisms in hadron production.

Abstract

The isospin symmetry, originating from similar masses of $u$ and $d$ quarks, if exact would result in equal numbers of charged ($K^+$ and $K^{-}$) and neutral ($K^0$ and $\overline{K}^0$) mesons produced in collisions of isospin-symmetric atomic nuclei. The charged and neutral $K$ meson production in Ar+Sc collisions at a center-of-mass energy of 11.9 GeV per nucleon pair was measured by the NA61/SHINE Collaboration. The production of charged $K$ mesons at mid-rapidity is (18.4$\pm$6.1)\% higher than that of the neutral $K$ mesons.The models of hadron production, including known isospin-symmetry breaking effects, cannot explain the measurements.