Symmetry between up and down quarks is more broken than expected

In late 2023, Wojciech Brylinski was analyzing data from the NA61/SHINE collaboration at CERN for his thesis when he noticed an unexpected anomaly—a strikingly large imbalance between charged and neutral kaons in argon–scandium collisions. He found that, instead of being produced in roughly equal numbers, charged kaons were produced 18.4% more often than neutral kaons.