Ⅱ-5. Hadron Physics (Theory)

RIKEN Accel. Prog. Rep. 49 (2016)

Anomalous chiral eﬀects in heavy ion collisions†J. Liao∗1,∗2Fig. 1. Correlations γHα ,Hβ vs centrality for 3-flavor case.

To draw a deﬁnitive conclusion, it is vital to develop anomalous hydrodynamic simulations that quantify the CME signals with realistic initial conditions
as well as account for background contributions. Recently a ﬁrst attempt has been made in4) to consistently quantify contributions to observed charge correlations from both the CME signal and background contributions in one and same framework that integrates
anomalous hydro with data-validated bulk viscous hy†∗1∗2

Condensed from the articles in Phys. Rev. D. 92, 071501(R)(2015) and in Phys. Lett. B 756, 42 (2016).
RIKEN Nishina Center
Department of Physics, Indiana University- 119 -ΛΩΛ

dro simulations. The anomalous hydrodynamic equations for pertinent currents are solved in a linearized
way on top of the bulk evolution. The results from thiscomputation have demonstrated that the same-charge
correlation data by STAR can be described quantitatively with CME and TMC together, computed withmodest magnetic ﬁeld lifetime (∼ 1fm/c) and realistic initial axial charge density. To further test thisinterpretation, predictions have been made for the azimuthal correlations of various identiﬁed hadron paris(see Fig. 1 ), to be compared with future data.

ΛAnomalous chiral eﬀects, notably the Chiral Magnetic Eﬀect (CME), are remarkable phenomena thatstem from highly nontrivial interplay of QCD chiralsymmetry, axial anomaly, and gluonic topology. It isof fundamental importance to search for these eﬀects inexperiments. The heavy ion collisions provide a uniqueenvironment where a hot chiral-symmetric quark-gluon
plasma is created, gluonic topological ﬂuctuations generate chirality imbalance, and very strong magnetic⃗ ∼ m2 are present during the early stage ofﬁelds |B|πsuch collisions. For recent reviews, see1–3) .
The CME predicts the generation of charge cur⃗ for a chiral medium inrent ⃗J along magnetic ﬁeld B⃗the presence of axial charge imbalance: ⃗J = CA µA B
where µA characterizes chirality imbalance. In noncentral heavy ion collisions, the CME may lead to anout-of-plane charge separation eﬀect, contributing tothe reaction-plane dependent azimuthal correlation observable: γHα Hβ =< cos(ϕi + ϕj − 2ΨRP ) >αβ withHα , Hβ labeling the hadron species and ϕi,j the azimuthal angles of the two ﬁnal state charged hadrons.
The ΨRP denotes reaction plane angle. However, themeasured correlation suﬀers from elliptic ﬂow driven
background contributions and can not be entirely attributed to CME. The separation of ﬂow-driven background and possible CME signal is the most pressing
issue in current CME search.

Fig. 2. Normalized Λ̄ and Λ elliptic flow splitting,f|AΛ[v2Λ̄ − v2Λ ]/[|qΩ± ], for symmetric 2-flavor(2-F) and 3flavor(3-F) cases (for 15−30% and 60−92% centrality).

Studying CME-related anomalous transport phenomena provides an independent avenue for the searchof CME. Global ﬂuid rotation (quantiﬁed by nonzero
vorticity ω⃗ ) bears close similarity to a magnetic ﬁeld⃗ and can induce Chiral Vortical Eﬀects (CVE). InB
the presence of ﬂuid rotation, a new gapless collective mode called Chiral Vortical Wave (CVW) has recently been found in5) . The CVW arises from interplay between vector and axial charge ﬂuctuations induced by CVE. For the rotating quark-gluon plasma in
non-central collisions, the CVW-induced charge transport leads to the formation of ﬂavor-wise quadrupole
in the ﬁreball. Such phenomenon could be manifested
through the elliptic ﬂow splitting of Λ and Λ̄ baryons(with predictions shown in Fig. 2) that may be experimentally measured.
References
1) D. E. Kharzeev, J. Liao, S. A. Voloshin and G. Wang,Prog. Part. Nucl. Phys. 88, 1 (2016).
2) J. Liao, Pramana 84, no. 5, 901 (2015).
3) J. Liao, arXiv:1601.00381 [nucl-th].
4) Y. Yin and J. Liao, Phys. Lett. B 756, 42 (2016).
5) Y. Jiang, X. G. Huang and J. Liao, Phys. Rev. D 92,
no. 7, 071501 (2015).