  The D0 Collaboration has reported an anomalous charge asymmetry in the
production of same-sign muon pairs at the Fermilab Tevatron. The magnitude of
this effect depends on the subtraction of several backgrounds, the most notable
of which is due to kaons being misidentified as muons either through decays in
flight or punch-through. The present authors suggested a check on such
backgrounds consisting of a tight restriction on the muon impact parameter $b$,
to confirm that this excess was indeed due to $B_{(s)}$ meson decays. The D0
Collaboration has performed a related check applying transverse impact
parameter (IP) restrictions, whose implications are discussed. We study
background asymmetry predictions for events involving two muons with IP bounds
which are complementary to each other. These predictions may be used in future
measurements of the net charge asymmetry from $B_{(s)}$ decays.
