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The research on 60Co beta decay has shown the symmetry breaking, but conservation of the CP (charge+parity) symmetry: in b- decay the electron is ejected down, in b+ decays - the anti-electron (positron) is ejected up.
A surprise came from neutral mesons K0, consisting of one d quark and one anti-quark s (and anti-meson K0 with d ands).
Their parity equals zero. These mesons can be considered as a mixture of two components - with parity CP=1 and CP=-1. The meson K0 with parity 1 decays after 0,9x10-10 s to two lighter mesons p+ and p- (consisting of u quark andd anti-quark or u and d, respectively); the meson with CP=-1 lives 500 times longer, because it may decay only to three mesons p0.
In 1964 there was observed however that about one out of 500 long-lived mesons K0 "change in flight" its parity to CP=1 and dies quicker. CP parity is not conserved!
Just in 1999 other experiments confirmed breaking the CP symmetry, however, always very small. Because simultaneously there are no observations, within the measurement error, of breaking the combined charge-parity-time symmetry (CPT), so the time arrow also is not asymmetrical
Like that
"celtic"
spin: slightly unsimmetrical, but rotates only in one direction.
Like the time arrow: it runs only forward and we (with a high scientific confidence level) get always older!
Also the Venetian gondola are slighty (by 15 cm) assymetric one one side - this allows to row just by one "gondoliere".