"Discoveries of Quasi-Stable Exotic Atoms and Nuclei Involving

Antiprotons, Pions and Kaons

— Their impacts on fundamental physics —"



Toshimitsu Yamazaki

Professor Emeritus, University of Tokyo



A review will be made on recently discovered anomalously long-lived atomic and nuclear bound states of antiprotons, pions and anti-kaons, which have hitherto been believed to be non-existing because of the strong nuclear absorptions.
i) Antiprotonic helium atom-molecule, a miraculously long-lived (for several microseconds, one million times longer than the usually believed cascade time), discovered in 1991 at KEK. As a unique interface between matter and antimatter, it provides information pertaining to CPT invariance.
ii) Deeply bound pionic nuclei, predicted in 1988 and first observed in 1996 at GSI. A recent experiment has revealed a partial restoration of chiral symmetry in the nuclear medium, thus proving the Nambu scenario concerning the origin of the large mass scale of hadrons.
iii) Extraordinarily dense strange nuclear systems mediated by anti-K mesons, predicted and discovered recently at KEK. The predicted bound systems, such as ppK‾, pppKh‾, ppK‾K‾ and pppK‾K‾, have very large binding energies and high densities (as much as 3 times the normal nuclear density). The first evidence was found at KEK.
They provide a hitherto unknown and untouched regime of particle-nuclear physics (high density, kaon condensation, cold quark-gluon phase).
Further experiments using kaons, pions, heavy ions, etc. are planned.






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