Subleading harmonic flows in hydrodynamic simulations of heavy ion collisions

Abstract

We perform a principal component analysis (PCA) of $v_3(p_T)$ in event-by-event hydrodynamic simulations of Pb+Pb collisions at the Large Hadron Collider (LHC). The PCA procedure identifies two dominant contributions to the two-particle correlation function, which together capture 99.9\% of the squared variance. We find that the subleading flow (which is the largest source of flow factorization breaking in hydrodynamics) is predominantly a response to the radial excitations of a third-order eccentricity. We present a systematic study of the hydrodynamic response to these radial excitations in 2+1D viscous hydrodynamics. Finally, we construct a good geometrical predictor for the orientation angle and magnitude of the leading and subleading flows using two Fourier modes of the initial geometry.

updated references, corrected typos, 12 pages, 14 figures