Testing the chiral magnetic and chiral vortical effects in heavy ion collisions

Abstract

We devise a test of the Chiral Magnetic and Chiral Vortical effects (CME and CVE) in relativistic heavy ion collisions that relies only on the general properties of triangle anomalies. We show that the ratio $R_{EB}=J_E/J_B$ of charge $J_E$ and baryon $J_B$ currents for CME is $R^{\rm CME}_{EB} \to \infty$ for three light flavors of quarks ($N_f =3$), and $R^{\rm CME}_{EB} = 5$ for $N_f =2$, whereas for CVE it is $R^{\rm CVE}_{EB} =0$ for $N_f =3$ and $R^{\rm CME}_{EB} = 1/2$ for $N_f =2$. The physical world with light $u,d$ quarks and a heavier $s$ quark is in between the $N_f =2$ and $N_f =3$ cases; therefore, the ratios $R_{EB}$ for CME and CVE should differ by over an order of magnitude. Since the ratio of electric charge and baryon asymmetries is proportional to $R_{EB}$, the measurement of baryon and electric charge asymmetry fluctuations should allow to separate clearly the CME and CVE contributions. In both cases, there has to be a positive correlation between the charge and baryon number asymmetries that can be tested on the event-by-event basis. At a lower collision energy, as the baryon number density increases and the CVE potentially plays a role, we expect the emergence of the baryon number asymmetry.