η′ meson under partial restoration of chiral symmetry in nuclear medium

In-medium modification of the η′ mass is discussed in the context of partial restoration of chiral symmetry in nuclear medium. We emphasize that the UA(1) anomaly effects cause the η′-η mass difference necessarily through the chiral symmetry breaking. As a consequence, the η′ mass is expected to be reduced by order of 100 MeV in nuclear matter where about 30% reduction of chiral symmetry takes place. The strong attraction relating to the η′ mass generation eventually implies that there should be also a strong attractive interaction in the scalar channel of the η′-N two-body system. We find that the attraction can be strong enough to form a bound state.