  The baryonic acoustic feature in galaxy clustering is a promising tool for
constraining the nature of the cosmic acceleration, through measurements of
expansion rates H and angular diameter distances D_A. Angle-averaged
measurements of clustering yield constraints on the quantity D_A^2/H. However,
to break the degeneracy between these two parameters one must measure the
anisotropic correlation function as a function of both line-of-sight (radial)
and transverse separations. Here we investigate how to most effectively do so,
using analytic techniques and mock catalogues. In particular, we examine
multipole expansions of the correlation function as well as "clustering wedges"
xi(Delta mu, s), where mu = s_||/s and s_|| is the radial component of
separation s. Both techniques allow strong constraints on H and D_A, as
expected. The radial wedges strongly depend on H and the transverse wedges are
sensitive to D_A. Analyses around the region of the acoustic peak constrain H
~20% better when using the wedge statistics than when using the
monopole-quadrupole combination. However, we show that the hexadecapole allows
substantially stronger constraints than the monopole and quadrupole alone. Our
findings here demonstrate that wedge statistics provide a practical alternative
technique to multipoles, that should be useful to test systematics and will
provide comparable or better constraints. Finally, we predict the constraints
from galaxy clustering that will be possible with a completed version of the
ongoing Baryonic Oscillation Spectroscopic Survey.
