Speaker
Description
Recently the splitting of elliptic flow $v_2$ at finite rapidities has
been proposed to be the result of global vorticity in non-central
relativistic heavy ion collisions [1]. Here we confirm the existence
of the $v_2$ splitting. However, we show that this left-right $v_2$
splitting (on opposite sides of the impact parameter axis) is mostly
due to the non-zero directed flow $v_1$ at finite rapidities, with the
splitting given by $v_2(p_x>0)-v_2(p_x<0)\sim 8v_1/3\pi$
[2]. It is thus expected to depend sensitively on the transverse
momentum, rapidity range, particle species, and colliding energy. We
then use a multi-phase transport model, which automatically includes
the vorticity field and flow fluctuations, to demonstrate these features.
We also find that the $v_2$ splitting contains a contribution from a
new type of triangular flow, which at finite rapidities correlates to
the reaction plane. In addition, the $v_2$ splitting measurement
does not necessarily need to measure the 1st-order event plane
$\Psi_1$; it only needs to know whether the 2nd-order event plane angle
$\Psi_2$ or $\pi+\Psi_2$ corresponds to the $p_x>0$ side. So the
left-right $v_2$ splitting contains similar but somewhat different
information compared to the conventional separate $v_1$ and $v_2$
measurements; and it could be easier to do. Therefore, this observable
should benefit the studies of the three-dimensional geometry and
evolution of the dense matter created in heavy ion collisions.
[1] Z. Chen, Z. Wang, C. Greiner, and Z. Xu, arXiv:2108.12735
[hep-ph].
[2] C. Zhang and Z.-W. Lin, 2109.04987 [nucl-th].
