  We investigate the equilibrium property of a mesoscopic ring with spin orbit
(SO) interaction. It is well known that for a normal mesoscopic ring threaded
by a magnetic flux, the electron acquires a Berry phase that induces the
persistent (charge) current. Similarly, the spin of electron acquires a spin
Berry phase traversing the ring with SO interaction. It is this spin Berry
phase that induces a persistent spin current. To demonstrate its existence, we
calculate the persistent spin current without accompanying charge current in
the normal region in a hybrid mesoscopic ring. We point out that this
persistent spin current describes the real spin motion and can be observed
experimentally.
