Measurements of mass-dependent azimuthal anisotropy in central $p$$+$Au, $d$$+$Au, and $^3$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

Understand

We present measurements of the transverse-momentum dependence of elliptic flow $v_2$ for identified pions and (anti)protons at midrapidity ($|\eta|<0.35$), in 0%--5% central $p$$+$Au and $^3$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV.

• When taken together with previously published measurements in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, the results cover a broad range of small-collision-system multiplicities and intrinsic initial geometries.
• We observe a clear mass-dependent splitting of $v_2(p_{T})$ in $d$$+$Au and $^3$He$+$Au collisions, just as in large nucleus-nucleus ($A$$+$$A$) collisions, and a smaller splitting in $p$$+$Au collisions.
• Both hydrodynamic and transport model calculations successfully describe the data at low $p_T$ ($< 1.5$ GeV/$c$), but fail to describe various features at higher $p_T$.