  We show that, contrary to the flavour mixing amplitude q/p, both Re(epsilon)
and Im(epsilon) are observable quantities, where epsilon is the phase-
convention-independent CP mixing. We consider semileptonic B_d decays from a CP
tag and build appropriate time-dependent asymmetries to separate out
Re(epsilon) and Im(epsilon). "Indirect" CP violation would have in
Im(epsilon)/(1+|epsilon|^2) its most prominent manifestation in the B-system,
with expected values in the standard model ranging from -0.37 to -0.18. This
quantity is controlled by a new observable phase: the relative one between the
CP-violating and CP-conserving parts of the effective hamiltonian. For
time-integrated rates we point out a (Delta Gamma)--> (Sigma Gamma)
transmutation which operates in the perturbative CP mixing.
