  Considering semileptonic decays of the entangled B^0 \bar B^0 state which is
generated in the decay of Upsilon(4S), we simply multiply the
quantum-mechanical interference term by a factor (1-\zeta) and use the
``decoherence parameter'' \zeta as a measure for deviations from quantum
mechanics. We investigate several consequences of this modification of
semileptonic B^0 \bar B^0 decays. In particular, we show that when confronted
with the experimental values of the ratio R=(# like-sign dilepton events)/(#
opposite-sign dilepton events) and of the B_H--B_L mass difference, the ensuing
one standard deviation range of the decoherence parameter depends strongly on
the basis in the B^0--\bar B^0 space used to build the entangled B^0 \bar B^0
state. On the other hand, in quantum mechanics physical quantities are, of
course, independent of such arbitrary basis choices.
