Measurements of azimuthal anisotropy and charged-particle multiplicity in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=$200, 62.4, 39, and 19.6 GeV

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We present measurements of the elliptic flow, $v_2$, as a function of transverse momentum ($p_T$), pseudorapidity ($\eta$), and centrality in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=$200, 62.4, 39, and 19.6 GeV.

• The beam-energy scan of $d$$+$Au collisions provides a testing ground for the onset of flow signatures in small collision systems.
• We measure a nonzero $v_2$ signal at all four collision energies, which, at midrapidity and low $p_T$, is consistent with predictions from viscous hydrodynamic models.
• Comparisons with calculations from parton transport models (based on the {\sc ampt} Monte Carlo generator) show good agreement with the data at midrapidity to forward ($d$-going) rapidities and low $p_T$.