https://doi.org/10.1140/epjc/s10052-025-14798-3
Letter
Isospin kaon anomaly and its consequences
Institute of Physics, Jan Kochanowski University, ul. Uniwersytecka 7, Kielce, Poland
a
rohrmoser.martin1987@gmail.com
Received:
22
April
2025
Accepted:
16
September
2025
Published online:
24
September
2025
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 
–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 
and the hyperon ratio 
. Finally, we extend the approach to antiquarks in the initial state, useful for e.g. pion–nucleus scattering reactions.
© The Author(s) 2025
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