  We study the clustering of LRG galaxies in the latest spectroscopic SDSS data
releases, DR6 and DR7, which sample over 1 Gpc^3/h^3 to z=0.47. The 2-point
correlation function $\xisp$ is estimated as a function of perpendicular
$\sigma$ and line-of-sight $\pi$ (radial) directions. We find a significant
detection of a peak at $r\simeq 110$Mpc/h, which shows as a circular ring in
the $\sigma-\pi$ plane. There is also significant evidence for a peak along the
radial direction whose shape is consistent with its originating from the
recombination-epoch baryon acoustic oscillations (BAO). A $\xisp$ model with no
radial BAO peak is disfavored at $3.2\sigma$, whereas a model with no
magnification bias is disfavored at $2\sigma$. The radial data enable, for the
first time, a direct measurement of the Hubble parameter $H(z)$ as a function
of redshift. This is independent from earlier BAO measurements which used the
spherically averaged (monopole) correlation to constrain an integral of $H(z)$.
Using the BAO peak position as a standard ruler in the radial direction, we
find: $H(z=0.24)= 79.69 \pm 2.32 (\pm 1.29)$ km/s/Mpc for z=0.15-0.30 and
$H(z=0.43)= 86.45 \pm 3.27 (\pm 1.69)$ km/s/Mpc for $z=0.40-0.47$. The first
error is a model independent statistical estimation and the second accounts for
systematics both in the measurements and in the model. For the full sample,
$z=0.15-0.47$, we find $H(z=0.34)= 83.80 \pm 2.96 (\pm 1.59)$ km/s/Mpc.
