Chiral symmetry restoration at high matter density observed in pionic atoms
Chiral symmetry restoration at high matter density observed in pionic atoms
复制标题
在介子原子中观察到高物质密度下的手性对称性恢复
DOI：
10.1038/s41567-023-02001-x
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发表时间：
2023
期刊：
影响因子：
19.6
通讯作者：
Nishi Takahiro et. al
中科院分区：
文献类型：
--
作者：
Bayar M.;Ikeno N.;Roca L.;Nishi Takahiro et. al
根据量子色动力学，真空不是一个空的空间，因为它充满了夸克-反夸克对。这对粒子与真空有相同的量子数，并形成凝聚态，因为量子色动力学的强相互作用太强而不能使真空空着。这种夸克-反夸克凝聚，即手征凝聚，打破了真空的手征对称性。手征凝聚体的期望值是手征对称性的序参量，在高温或高物质密度下，手征对称性部分恢复，期望值会降低。在超相对论能量下的原子核迎头碰撞已经探索了高温区域，但在高密度下的实验很少。在这里，我们测量了π介子121 Sn原子的光谱，并研究了π介子与核之间的相互作用。我们发现，手征凝聚体的期望值降低在有限密度相比，在真空中的值。减少线性外推到核饱和密度，并表明手征对称性部分恢复，由于极高的密度的核。
According to quantum chromodynamics, vacuum is not an empty space, because it is filled with quark–antiquark pairs. The pair has the same quantum numbers as the vacuum and forms a condensate because the strong interaction of the quantum chromodynamics is too strong to leave the vacuum empty. This quark–antiquark condensation, the chiral condensate, breaks the chiral symmetry of the vacuum. The expectation value of the chiral condensate is an order parameter of the chiral symmetry, which is expected to decrease at high temperatures or high matter densities where the chiral symmetry is partially restored. Head-on collisions of nuclei at ultra-relativistic energies have explored the high-temperature regime, but experiments at high densities are rare. Here we measure the spectrum of pionic121Sn atoms and study the interaction between the pion and the nucleus. We find that the expectation value of the chiral condensate is reduced at finite density compared to the value in vacuum. The reduction is linearly extrapolated to the nuclear saturation density and indicates that the chiral symmetry is partially restored due to the extremely high density of the nucleus.