  The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC)
reports measurements of azimuthal dihadron correlations near midrapidity in
$d$$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV. These measurements
complement recent analyses by experiments at the Large Hadron Collider (LHC)
involving central $p$$+$Pb collisions at $\sqrt{s_{_{NN}}}$=5.02 TeV, which
have indicated strong anisotropic long-range correlations in angular
distributions of hadron pairs. The origin of these anisotropies is currently
unknown. Various competing explanations include parton saturation and
hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies
in $d$$+$Au collisions compared to those seen in $p$$+$Pb collisions at the
LHC. The larger extracted $v_2$ values in $d$$+$Au collisions at RHIC are
consistent with expectations from hydrodynamic calculations owing to the larger
expected initial-state eccentricity compared with that from $p$$+$Pb
collisions. When both are divided by an estimate of the initial-state
eccentricity the scaled anisotropies follow a common trend with multiplicity
that may extend to heavy ion data at RHIC and the LHC, where the anisotropies
are widely thought to arise from hydrodynamic flow.
