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

Abstract

We present measurements of the transverse-momentum dependence of elliptic flow $v_2$ for identified pions and (anti)protons at midrapidity ($|\hat{I}\cdot |<0.35$), 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($K{E}_T/n_q$), which was also seen previously in $A$$+$$A$ collisions.

353 authors, 12 pages, 7 figures, 3 tables. v2 is version accepted for publication in Phys. Rev. C. Data tables are included in the Appendix. Plain text data tables for points plotted in figures for other PHENIX publications are publicly available at http://www.phenix.bnl.gov/papers.html