Search for the chiral magnetic effect in heavy ion collisions

Abstract

The interplay between the chiral anomaly and the strong magnetic or vortical fields created in noncentral heavy-ion collisions can lead to various anomalous chiral effects in the quark-gluon plasma, including the chiral magnetic effect (CME), the chiral magnetic wave (CMW), and the chiral vortical effect (CVE). In this proceeding, recent ALICE measurements of these effects are summarized. Utilizing Event Shape Engineering, fractions of CME and CMW signals extracted in Pb-Pb collisions at √ s NN = 5.02 TeV are consistent with zero within uncertainties. The CVE is studied using azimuthal correlations between baryon pair Λ-p with Λ-h and h-h as reference. These measurements provide new insights into the experimental search for anomalous chiral effects in heavy-ion collisions.

Lambda polarization in $^{108}$Ag +$^{108}$Ag and $^{197}$Au +$^{197}$Au collisions around a few GeV

“…We will leave such theoretical study to future work. Besides, we also plan to study the global Λ polarization in isobar collisions [60][61][62] which may help to understand whether the magnetic field is the source for the splitting of Λ and Λ polarization.…”

Charge-dependent transverse momentum and its impact on the search for the chiral magnetic wave

“…We start with the contribution from the resonance decay in a given event with ρ 0 → π + π − . Such a typical dynamic process of LCC has proven to be a significant background in the search for the CME [4,9]. In Fig.…”

“…the Chiral Magnetic Effect (CME), the Chiral Separation Effect (CSE), and the Chiral Magnetic Wave (CMW) [5][6][7][8]. As CME could manifest itself in a finite electric dipole moment with respect to the reaction plane [9], the CMW is expected to generate an electric quadrupole moment in the quark-gluon plasma (QGP), where the "poles" (outof-plane) and the "equator" (in-plane) of the participant region respectively acquire additional positive or negative charges. Taking advantage of the anisotropic emission of particles in azimuthal direction, it is feasible to measure the CMW using the charge asymmetry (A ch ) dependence of elliptic flow (v 2 ) between the positively and negatively charged particles, i.e.,…”

Interpreting the charge-dependent flow and constraining the chiral magnetic wave with event shape engineering

“…Though early measurements suggest some similarities between the observables and the theoretical expectations, there is considerable evidence that the background effects play a dominant role in the experimental measurement. In the CME study, for instance, the γ correlator originally aiming at detecting the electric dipole moment proportionally varies as the elliptic flow (v 2 ) and the invariant mass of the particle pairs change [10], indicating the contribution from the local charge conservation (LCC) and/or transverse momentum conservation (TMC) entwined with collective flow. In recent years, substantial attempts are made to extract the fraction of the potential CME signal.…”