Search for the chiral magnetic effect in heavy ion collisions

Quark interactions with topological gluon fields in quantum chromodynamics can yield local P and CP violations that could explain the matter–antimatter asymmetry in our universe. Effects of P and CP violations can lead to charge separation under a strong magnetic field, a phenomenon called the chiral magnetic effect(CME).Early measurements of the CME-induced charge separation in heavy ion collisions are dominated by physics backgrounds. This report discusses the recent innovative efforts in eliminating those backgrounds, namely by eventshape engineering, invariant mass dependence, and reaction and participant plane comparison. The backgroundfree CME measurements using these novel methods are presented.

Chiral Magnetic Effect and Chiral Phase Transition

我们在 chiral 上学习 chiral 阶段转变的影响磁性的效果。温度的功能是计算的方位角的费用粒子关联。当温度为 QCD 阶段转变到达它的批评价值，在关联有一个显著尖顶，这被发现当温度为 QCD 阶段转变到达它的批评价值。当在 RHIC 的碰撞精力减少到，将有费用粒子关联的激烈的抑制，这被预言当在 RHIC 的碰撞精力减少到在批评价值下面。我们然后证明方位角的费用粒子关联能是信号在 RHIC 精力扫描实验识别 QCD 阶段转变的出现。

Asymmetric scattering behaviors of spin wave dependent on magnetic vortex chirality

We investigate asymmetric spin wave scattering behaviors caused by vortex chirality in a cross-shaped ferromagnetic system by using the micromagnetic simulations.In the system,four scattering behaviors are found:(i)asymmetric skew scattering,depending on the polarity of vortex core,(ii)back scattering(reflection),depending on the vortex core stiffness,(iii)side deflection scattering,depending on structural symmetry of the vortex circulation,and(iv)geometrical scattering,depending on waveguide structure.The first and second scattering behaviors are attributed to nonlinear topological magnon spin Hall effect related to magnon spin-transfer torque effect,which has value for magnonic exploration and application.

Estimation of the chiral magnetic effect considering the magnetic field response of the QGP medium

The magnetic field plays a major role in searching for the chiral magnetic effect in relativistic heavy-ion collisions. If the lifetime of the magnetic field is too short, as predicted by simulations of the field in vacuum, the chiral magnetic effect will be largely suppressed. However, the lifetime of the magnetic field will become longer when the QGP medium response is considered. We give an estimate of the effect, especially considering the magnetic field response of the QGP medium, and compare it with the experimental results for the background-subtracted correlator H at RHIC and LHC energies. The results show that our method explains the experimental results better at the top RHIC energy than at the LHC energy.

A systematical study of the chiral magnetic effects at the RHIC and LHC energies

Considering the magnetic field response of the QGP medium,we perform a systematical study of the chiral magnetic effect(CME),and make a comparison with the experimental results for the background-subtracted correlator H at the energies of the RHIC Beam Energy Scan(BES)and the LHC energy.The CME signals from our computations show a centrality trend and beam energy dependence that are qualitatively consistent with the experimental measurements of the charge dependent correlations.The time evolution of the chiral electromagnetic current at the RHIC and LHC energies is systematically studied.The dependence of the time-integrated current signal on the beam energy√s with different centralities is investigated.Our phenomenological analysis shows that the time-integrated electromagnetic current is maximal near the collision energy√s≈39 GeV.The qualitative trend of the induced electromagnetic current is in agreement with the CME experimental results at the RHIC and LHC energies.

Current-driven transformations of a skyrmion tube and a bobber in stepped nanostructures of chiral magnets

Magnetic skyrmion tubes and bobbers are two types of different nanoscale spin configurations that can coexist in nanostructures of chiral magnets.They are then proposed to be utilized as binary bits to build racetrack memory devices.The ability to manipulate the two magnetic objects controllably by current in nanostructures is the prerequisite to realize the device.Here,we demonstrate by numerical simulations that a magnetic bobber and a skyrmion tube can be transformed to each other using spinpolarized current in nanostripes with stepped shape.We also show such stepped nanostructures can be readily applied as the write head for the skyrmion-bobber-based racetrack memory.

Varying the chiral magnetic effect relative to flow in a single nucleus-nucleus collision

We propose a novel method to search for the chiral magnetic effect（cme） in heavy ion collisions.We argue that the relative strength of the magnetic field（mainly from spectator protons and responsible for the cme）with respect to the reaction plane and the participant plane is opposite to that of the elliptic flow background arising from the fluctuating participant geometry.This opposite behavior in a single collision system,hence with small systematic uncertainties,can be exploited to extract the possible cme signal from the flow background.The method is applied to existing data from rhic,and the outcome discussed.

Investigation of experimental observables in search of the chiral magnetic effect in heavy-ion collisions in the STAR experiment

The chiral magnetic effect(CME)is a novel transport phenomenon,arising from the interplay between quantum anomalies and strong magnetic fields in chiral systems.In high-energy nuclear collisions,the CME may survive the expansion of the quark-gluon plasma fireball and be detected in experiments.Over the past two decades,experimental searches for the CME have attracted extensive interest at the Relativistic Heavy Ion Collider(RHIC)and the Large Hadron Collider(LHC).The main goal of this study is to investigate three pertinent experimental approaches:the$\gamma$correlator,the R correlator,and the signed balance functions.We exploit simple Monte Carlo simulations and a realistic event generator(EBE-AVFD)to verify the equivalence of the core components among these methods and to ascertain their sensitivities to the CME signal and the background contributions for the isobar collisions at the RHIC.

Chiral magnetic effect in isobar collisions from stochastic hydrodynamics

We studied the chiral magnetic effect in AuAu,RuRu,and ZrZr collisions at sNN−√=200GeV.The axial charge evolution was modeled with stochastic hydrodynamics,and geometrical quantities were calculated with the Monte Carlo Glauber model.By adjusting the relaxation time of the magnetic field,we found our results are in good agreement with background subtracted data for AuAu collisions at the same energy.We also made predictions for RuRu and ZrZr collisions.We found a weak centrality dependence on initial chiral imbalance,which implies that the centrality dependence of chiral magnetic effect signals results mainly from the effects of the magnetic field and volume factor.Furthermore,our results show an unexpected dependence on system size.While the AuAu system has larger chiral imbalance and magnetic field,it was observed to have a smaller signal for the chiral magnetic effect due to the larger volume suppression factor.

Status of the chiral magnetic effect and collisions of isobars

In this review, we examine the current theoretical and experimental status of the chiral magnetic effect.We discuss possible future strategies for resolving uncertainties in interpretation including recommendations for theoretical work, recommendations for measurements based on data collected in the past five years, and recommendations for beam use in the coming years of RHIC. We specifically investigate the case for colliding nuclear isobars（nuclei with the same mass but different charge） and find the case compelling. We recommend that a program of nuclear isobar collisions to isolate the chiral magnetic effect from background sources be placed as a high priority item in the strategy for completing the RHIC mission.

Quantifying the chiral magnetic effect from anomalous-viscous fluid dynamics

The Chiral Magnetic Effect（CME） is a macroscopic manifestation of fundamental chiral anomaly in a many-body system of chiral fermions, and emerges as an anomalous transport current in the fluid dynamics framework. Experimental observation of the CME is of great interest and has been reported in Dirac and Weyl semimetals. Significant efforts have also been made to look for the CME in heavy ion collisions. Critically needed for such a search is the theoretical prediction for the CME signal. In this paper we report a first quantitative modeling framework, Anomalous Viscous Fluid Dynamics（AVFD）, which computes the evolution of fermion currents on top of realistic bulk evolution in heavy ion collisions and simultaneously accounts for both anomalous and normal viscous transport effects. AVFD allows a quantitative understanding of the generation and evolution of CME-induced charge separation during the hydrodynamic stage, as well as its dependence on theoretical ingredients. With reasonable estimates of key parameters, the AVFD simulations provide the first phenomenologically successful explanation of the measured signal in 200 AGe V Au Au collisions.

Chiral structures and tunable magnetic moments in 3d transition metal doped Pt_6 clusters

The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt6 （M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn） are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital （HOMO） lowest unoccupied molecular orbital （LUMO） gaps suggest that the doped clusters can have higher chemical activities than the pure Pt7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt6 clusters is from 0 μB to 7 μB, revealing that the MPt6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties.

Chiral phase transition of quark matter in the background of parallel electric and magnetic fields

We report on our results about spontaneous chiral symmetry breaking for quark matter in the background of static and homogeneous parallel electric field,E,and magnetic field,B.A Nambu–Jona–Lasinio model is used to compute the dependence of the chiral condensate at finite temperature,E and B.We study the effect of this background on inverse catalysis of chiral symmetry breaking for E and B of the same order of magnitude.We also consider the effect of equilibration of chiral density,n_5,produced by axial anomaly on the critical temperature.The equilibration of n_5 allows for the introduction of the chiral chemical potential,u_5,which is computed selfconsistently as a function of temperature and field strength.We find that even if the chiral medium is produced by the fields the thermodynamics,with particular reference to the inverse catalysis induced by the external fields,it is not very affected by n_5 at least if the average u_5,at equilibrium is not too large.

Magnetism of Co₁₃-Filled Carbon Nanotubes of Diverse Chiral Symmetry

The attempt to study magnetism in (n,m) chiral space of single-walled carbon nanotubes (SWNTs) with embedded metal cluster is presented. Co13 metallic cluster inside zigzag and chiral single-walled nanotubes was investigated using density functional theory (DFT). Magnetic properties of the endohedral nanotubes with the various chiral index (n,m) were characterized by calculation of the total spin magnetic moment (S). The dependence of S on the chiral symmetry of nanotubes, as well as the orientation of Co13 cluster within nanotubes was found. Longitudinal orientation of icosahedral Co13 cluster was preferable for magnetization in general. However, it was shown that the magnetic landscape M = f(n,m) of endohedral nanotubes is very complex and sharp.

Anomalous chiral transports and spin polarization in heavy-ion collisions

Relativistic heavy-ion collisions create hot quark–gluon plasma as well as very strong electromagnetic(EM)and fluid vortical fields.The strong EM field and vorticity can induce intriguing macroscopic quantum phenomena such as chiral magnetic,chiral separation,chiral electric separation,and chiral vortical effects as well as the spin polarization of hadrons.These phenomena provide us with experimentally feasible means to study the nontrivial topological sector of quantum chromodynamics,the possible parity violation of strong interaction at high temperature,and the subatomic spintronics of quark–gluon plasma.These studies,both in theory and in experiments,are strongly connected with other subfields of physics such as condensed matter physics,astrophysics,and cold atomic physics,and thus form an emerging interdisciplinary research area.We give an introduction to the aforementioned phenomena induced by the EM field and vorticity and an overview of the current status of experimental research in heavy-ion collisions.We also briefly discuss spin hydrodynamics as well as chiral and spin kinetic theories.

Recent developments in chiral and spin polarization effects in heavy-ion collisions

We give a brief overview of recent theoretical and experimental results on the chiral magnetic effect and spin polarization effect in heavy-ion collisions.We present updated experimental results for the chiral magnetic effect and related phenomena.The time evolution of the magnetic fields in different models is discussed.The newly developed quantum kinetic theory for massive fermions is reviewed.We present theoretical and experimental results for the polarization of K hyperons and the q00 value of vector mesons.

Dynamics of magnetic skyrmions

We review the recent progress on the magnetic skyrmions in chiral magnetic materials. The magnetic skyrmion is a topological spin configuration with localized spatial extent, which could be thought of as an emergent rigid particle, owing to its particular topological and chiral properties. Static skyrmionic configurations have been found in various materials with different transport and thermodynamic properties. The magnetic skyrmions respond to externally applied fields in a very unique way, and their coupling to other quasiparticles in solid-state systems gives rise to the emergent electrodynamics.Being not only theoretically important, the magnetic skyrmion is also very promising to be the information carrier in next generation spintronic devices.

重子磁矩的协变手征有效理论研究

在SU(3)协变手征有效理论框架下,使用扩展的极小减除(extended minimal subtraction,EMS)方案,计算了至次领头阶(next-to-leading order,NLO)的重子质量和重子磁矩的一圈图修正贡献,并使用实验数据与PACS-CS格点数据组的数据对解析结果进行了数值拟合.结果表明,在NLO重子质量和重子磁矩的修正贡献中,EMS方案可以给出不错的理论结果和数值拟合的结果;该结果相较于重重子方法和红外正规化方法的结果更加优秀,并且与EOMS(extended-on-mass-shell)方案的结果相近.

Study of Ratio of Proton Momentum Distributions with a Chiral Quark Model

The ratio between the anomalous magnetic moments of proton and neutron has recently been suggested to be connected to the ratio of proton momentum fractions carried by the valence quarks inside it. This moment fraction ratio is respectively evaluated by using constituent quark model and chiral quark model in order to check meson cloud effect. Our results show that the meson cloud effect is remarkable to the ratio of the proton momentum fractions, and therefore, this ratiois a sensitive test for the meson cloud effect as well as for the SU(6) symmetry breaking effect.

手征化学势下的手征相变研究

利用两味道的NJL模型,研究手征化学势对手征相变临界点的影响,并考虑了均匀磁场的情况.通过对质量隙方程的求解,得出夸克的有效质量随温度等的变化情况,确定相变临界点.在研究过程中采取三维动量截断的正规化处理方式.研究表明:随着手征化学势的不断增大,临界化学势不断减小,而临界温度先增加后减小,这反映了手征化学势对手征对称性破缺的催化和逆催化效应;而磁场的增强会对手征对称性破缺起到强化作用,导致有效质量增大,临界化学势、临界手征化学势以及临界温度也会随之增大.此外,也简单地讨论了有限体积效应.