  We report on measurements of sequential $\Upsilon$ suppression in Au+Au
collisions at $\sqrt{s_{_\mathrm{NN}}}$ = 200 GeV with the STAR detector at the
Relativistic Heavy Ion Collider (RHIC) through both the dielectron and dimuon
decay channels. In the 0-60% centrality class, the nuclear modification factors
($R_{\mathrm{AA}}$), which quantify the level of yield suppression in heavy-ion
collisions compared to $p$+$p$ collisions, for $\Upsilon$(1S) and
$\Upsilon$(2S) are $0.40 \pm 0.03~\textrm{(stat.)} \pm 0.03~\textrm{(sys.)} \pm
0.09~\textrm{(norm.)}$ and $0.26 \pm 0.08~\textrm{(stat.)} \pm
0.02~\textrm{(sys.)} \pm 0.06~\textrm{(norm.)}$, respectively, while the upper
limit of the $\Upsilon$(3S) $R_{\mathrm{AA}}$ is 0.17 at a 95% confidence
level. This provides experimental evidence that the $\Upsilon$(3S) is
significantly more suppressed than the $\Upsilon$(1S) at RHIC. The level of
suppression for $\Upsilon$(1S) is comparable to that observed at the much
higher collision energy at the Large Hadron Collider. These results point to
the creation of a medium at RHIC whose temperature is sufficiently high to
strongly suppress excited $\Upsilon$ states.
