Symmetry between up and down quarks is more broken than expected

This article has been reviewed according to Science X's editorial process and policies . Editors have highlighted the following attributes while ensuring the content's credibility: NA61/SHINE’s lead-scintillator calorimeter. Credit: CERN 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. This suggested that the so-called "isospin symmetry" between up and down quarks might be broken by more than expected due to the differences in their electric charges and masses—a discrepancy that existing theoretical models would struggle to explain. Known sources of isospin asymmetry only predict deviations of a few percent. "When Wojciech got started, we thought it would be a triv ... Read full article.