New method to detect rotation in high-energy heavy-ion collisions

With increasing beam energies the angular momentum of the fireball in peripheral heavy-ion collisions increases, and the proposed differential Hanbury Brown and Twiss analysis is able to estimate this angular momentum quantitatively. The method detects specific space-time correlation patterns, which are connected to rotation.

Figure 1

Dependence of the standard correlation function in the ${\mathit{k}}_{+}$ direction from the collective flow, at the final time, 3.56 fm/$c$ after reaching local equilibrium and 8.06 fm/$c$ from the first touch, including the initial longitudinal expansion Yang-Mills field dynamics [19].

Figure 2

Differential correlation function, $\Delta C(k,q)$, at the final time with and without rotation.

Figure 3

Sketch of the configuration in different reference frames, with and without rotation of the flow. The nonrotating configurations may have radial flow velocity components only. The DCF, $\Delta C_{\alpha }(k,q)$, is evaluated in a $K^{\prime }$ reference frame rotated by an angle $\alpha$ in the $x,z$, reaction plane. We search for the angle $\alpha$, where the nonrotating configuration is “symmetric,” so that it has a “minimal” DCF as shown in Fig. 4.

Figure 4

The DCF at average pion wave number $k=5/$fm and fluid dynamical evolution time $t=3.56$ fm/$c$, as a function of the functions of momentum difference in the “out” direction $q$ (in units of 1/fm). The DCF is evaluated in a frame rotated in the reaction plane, in the c.m. system, by angle $\alpha$.

Figure 5

The DCF with and without rotation in the reference frames, deflected by the angle $\alpha$, where the rotationless DCF is vanishing or minimal. In this frame the DCF of the original, rotating configuration indicates the effect of the rotation only. The amplitude of the DCF of the original rotating configuration doubles for the higher energy (higher angular momentum) collision.