An improved measurement of baryon acoustic oscillations from the
  correlation function of galaxy clusters at $z \sim 0.3$
  We detect the peak of baryon acoustic oscillations (BAO) in the two-point
correlation function of a spectroscopic sample of $25226$ clusters selected
from the Sloan Digital Sky Survey. Galaxy clusters, as tracers of massive dark
matter haloes, are highly biased structures. The linear bias $b$ of the sample
considered in this work, that we estimate from the projected correlation
function, is $b \sigma_8 = 1.72 \pm 0.03$. Thanks to the high signal in the
cluster correlation function and to the accurate spectroscopic redshift
measurements, we can clearly detect the BAO peak and determine its position,
$s_p$, with high accuracy, despite the relative paucity of the sample. Our
measurement, $s_p = 104 \pm 7 \, \mathrm{Mpc} \, h^{-1}$, is in good agreement
with previous estimates from large galaxy surveys, and has a similar
uncertainty. The BAO measurement presented in this work thus provides a new
strong confirmation of the concordance cosmological model and demonstrates the
power and promise of galaxy clusters as key probes for cosmological
applications based on large scale structures.
