Year: 2025
Type: article
Abstract: Isospin symmetry is well fulfilled in the QCD vacuum, as evidenced by small mass differences of isospin partners and suppressed isospin-violating decays. Recently, the NA61/SHINE collaboration reported an unexpectedly large isospin-violating charged-to-neutral kaon ratio in Ar-Sc heavy-ion collisions (HIC). Using a quark recombination approach, we introduce a function of kaon multiplicities that reduces to unity in the isospin-symmetric limit independently of the scattering energy and type of nuclei. Using this quantity, we show that nucleus–nucleus collisions violate isospin sizably (at the $$6.4\sigma $$ 6.4 σ –level), while proton-proton data on kaon multiplicities do not. We predict other isospin-violating enhancements in HIC, such as the proton-to-neutron ratio $$p/n \sim 1.2$$ p / n ∼ 1.2 and the hyperon ratio $$\Sigma ^{+}/\Sigma ^{-}\sim 1.4$$ Σ + / Σ - ∼ 1.4 . Finally, we extend the approach to antiquarks in the initial state, useful for e.g. pion–nucleus scattering reactions.
Source: The European Physical Journal C
Authors: Francesco Giacosa, Martin Rohrmoser
Institution: Jan Kochanowski University
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W4414475385