Chiral symmetry restored at high matter density: new experimental evidence.

Researchers at the RIKEN Nishina Center for Accelerator-Based Science and other institutes worldwide have gathered experimental insights of the medium effects in nuclei at lower temperatures. They used spectroscopy techniques to measure the states of in (Sn) pionic atoms, bound systems consisting of a pion and atomic nucleus. The team set out to deduce the expected value of quark–antiquark pairs in the QCD vacuum by measuring pionic atoms at high densities and lower temperatures with high-precision spectroscopy techniques. The researchers found that their measurements were consistent with the spontaneous breakdown of the QCD vacuum's chiral symmetry described by Nambu's theory.