2 research outputs found
Pionic atom unveils hidden structure of QCD vacuum
Modern theories of physics tell that the vacuum is not an empty space. Hidden
in the vacuum is a structure of anti-quarks and quarks . The
and pair has the same quantum number as the vacuum and
condensates in it since the strong interaction of the quantum chromodynamics
(QCD) is too strong to leave it empty. The condensation breaks the
chiral symmetry of the vacuum. The expectation value is an order
parameter. For higher temperature or higher matter-density,
decreases reflecting the restoration of the symmetry. In contrast to these
clear-cut arguments, experimental evidence is so far limited. First of all, the
is nothing but the vacuum itself. It is neither visible nor
perceptible. In this article, we unravel this invisible existence by high
precision measurement of pionic atoms, -meson-nucleus bound systems.
Using the as a probe, we demonstrate that is reduced in
the nucleus by a factor of 58 4% compared with that in the vacuum. This
reduction indicates that the chiral symmetry is partially restored due to the
extremely high density of the nucleus. The present experimental result clearly
exhibits the existence of the hidden structure, the chiral condensate, in the
vacuum