Measurements of elliptic and triangular flow in high-multiplicity $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

TL;DR

This study measures elliptic and triangular flow in high-multiplicity $^{3}$He$+$Au collisions at 200 GeV, providing evidence for collective behavior and possible quark-gluon plasma formation in small systems.

Contribution

First measurement of $v_2$ and $v_3$ flow coefficients in $^{3}$He$+$Au collisions at 200 GeV, comparing experimental data with hydrodynamic models.

Findings

Collective effects dominate the observed correlations.

$v_2$ values are similar to those in $d$+Au collisions.

Hydrodynamic models with hot spots agree with the data.

Abstract

We present the first measurement of elliptic ($v_2$) and triangular ($v_3$) flow in high-multiplicity $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in $^{3}$He$+$Au and in $p$$+$$p$ collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the $^{3}$He$+$Au system. The collective behavior is quantified in terms of elliptic $v_2$ and triangular $v_3$ anisotropy coefficients measured with respect to their corresponding event planes. The $v_2$ values are comparable to those previously measured in $d$$+$Au collisions at the same nucleon-nucleon center-of-mass energy. Comparison with various theoretical predictions are made, including to models where the hot spots created by the impact of the three $^{3}$He nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.