Chiral Magnetic Wave at Finite Baryon Density and the Electric Quadrupole Moment of the Quark-Gluon Plasma

Abstract

The chiral magnetic wave is a gapless collective excitation of quark-gluon plasma in the presence of an external magnetic field that stems from the interplay of chiral magnetic and chiral separation effects; it is composed of the waves of the electric and chiral charge densities coupled by the axial anomaly. We consider a chiral magnetic wave at finite baryon density and find that it induces the electric quadrupole moment of the quark-gluon plasma produced in heavy ion collisions: the "poles" of the produced fireball (pointing outside of the reaction plane) acquire additional positive electric charge, and the "equator" acquires additional negative charge. We point out that this electric quadrupole deformation lifts the degeneracy between the elliptic flows of positive and negative pions leading to v(2)(π(+))<v(2)(π(-)), and estimate the magnitude of the effect.

Search for Chiral Magnetic Effects in High-Energy Nuclear Collisions

“…The results are shown in Fig. 2, together with the simulation calculations with UrQMD event generator [23] and with the theoretical calculations with the CMW effect with different duration times for the magnetic field [14]. For most data points, the slopes are positive and reach a maximum in mid-celtral/mid-peripheral collisions.…”

“…The CMW manifests itself in a finite electric quadrupole moment of the collision system, where the "poles" ("equator") of the produced fireball acquire additional positive (negative) charge [14]. This effect, if realized, will be reflected in the measurement of chargedependent elliptic flow.…”

“…In a chirally symmetric phase, the CME and CSE effects form a collective excitation, Chiral Magnetic Wave (CMW), a long wavelength hydrodynamic mode of chiral charge densities [14,15]. The CMW manifests itself in a finite electric quadrupole moment of the collision system, where the "poles" ("equator") of the produced fireball acquire additional positive (negative) charge [14].…”

Charge-dependent anisotropic flow studies and the search for the Chiral Magnetic Wave in ALICE

“…for some p T selection and, more importantly, some η acceptance. Indeed, this observable has been proposed theoretically [4] and measured experimentally in Au-Au collisions at √ s NN = 200 GeV by the STAR collaboration [5]. However, one of the issues with this observable is that the slope of v n vs A is not independent of experimental effects (for example tracking efficiency) and therefore requires a correction factor.…”

“…The lower row of the figure shows the same schematic for the opposite case with µ V < 0, which leads to exactly the same effect with all signs flipped. A detailed explanation and derivation of how the presence of CMW affects the final state observables in this way is given in [4] …”