Measurements of mass-dependent azimuthal anisotropy in central p0+Au, and ${}^3$He$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV

We present measurements of the transverse-momentum dependence of elliptic flow $v_2$ for identified pions and (anti)protons at midrapidity ($\mathrm{\mid }\eta \mathrm{\mid }<0.35$), 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 $p_T$. In all systems, the $v_2$ values follow an approximate quark-number scaling as a function of the hadron transverse kinetic energy per constituent quark($K{E}_T\mathrm{/}{n}_q$), which was also seen previously in $A$$+$$A$ collisions.