First analysis of anisotropic flow with Lee–Yang zeros

We report on the first analysis of directed and elliptic flow with the new method of Lee–Yang zeros. Experimental data are presented for Ru+Ru reactions at 1.69A GeV measured with the FOPI detector at SIS/GSI. The results obtained with several methods, based on the event-plane reconstruction, on Lee–Yang zeros, and on multiparticle cumulants (up to fifth order) applied for the first time at SIS energies, are compared. They show conclusive evidence that azimuthal correlations between nucleons and composite particles at this energy are largely dominated by anisotropic flow.

Figure 1

(Color online) $|G^{\theta }(\mathit{ir})|$ versus r for $\theta =0$. A zoom of $|G^{\theta }(\mathit{ir})|$ [Eq. (4)] around its first minimum is shown in the insert and the solid line is just to guide the eye. See text for details.

Figure 2

(Color online) $v_1$ versus transverse momentum for protons (upper panel) and deuterons (lower panel) measured in semicentral events and in a rapidity window in backward hemisphere. See text for details.

Figure 3

(Color online) $v_2$ versus transverse momentum for protons measured in semicentral events and around midrapidity. See text for details.