Measurements of elliptic and triangular flow in high-multiplicity HeAu collisions at GeV
A. Adare · S. Afanasiev · C. Aidala · N.N. Ajitanand · Y. Akiba · R. Akimoto · H. Al-Bataineh · J. Alexander · M. Alfred · H. Al-Ta'ani · K.R. Andrews · A. Angerami and 619 other authors
We present the first measurement of elliptic () and triangular () flow in high-multiplicity HeAu collisions at GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in HeAu and in collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the HeAu system. The collective behavior is quantified in terms of elliptic and triangular anisotropy coefficients measured with respect to their corresponding event planes. The values are comparable to those previously measured in 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 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.