Chiral symmetry restoration at high matter density observed in pionic atoms

According to quantum chromodynamics, vacuum is not an empty space, because it filled with quark–antiquark pairs. The pair has the same numbers as and forms a condensate strong interaction of chromodynamics too leave empty. This condensation, chiral condensate, breaks symmetry vacuum. expectation value order parameter symmetry, which expected decrease at high temperatures or matter densities where partially restored. Head-on collisions nuclei ultra-relativistic energies have explored high-temperature regime, but experiments are rare. Here we measure spectrum pionic 121Sn atoms study between pion nucleus. We find that reduced finite density compared in reduction linearly extrapolated nuclear saturation indicates restored due extremely In condensation pairs Experiments tin demonstrate densities.