<p>We investigate the signal of the chiral magnetic effect (CME) in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions and isobar collisions of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mmultiscripts><mi>Ru</mi><mprescripts></mprescripts><mn>44</mn><mn>96</mn></mmultiscripts><mo>+</mo><mmultiscripts><mi>Ru</mi><mprescripts></mprescripts><mn>44</mn><mn>96</mn></mmultiscripts></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mmultiscripts><mi>Zr</mi><mprescripts></mprescripts><mn>40</mn><mn>96</mn></mmultiscripts><mo>+</mo><mmultiscripts><mi>Zr</mi><mprescripts></mprescripts><mn>40</mn><mn>96</mn></mmultiscripts></mrow></math> in the newly developed chiral anomaly transport module based on the state-of-the-art model “a multiphase transport.” Our numerical simulation results for the ratio charge correlation <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Δ</mi><mi>γ</mi></mrow></math> in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Ru</mi><mo>+</mo><mi>Ru</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Zr</mi><mo>+</mo><mi>Zr</mi></mrow></math> collisions are close to the latest experimental data. The simulation shows that the CME signal is larger in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Ru</mi><mo>+</mo><mi>Ru</mi></mrow></math> collisions than that in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Zr</mi><mo>+</mo><mi>Zr</mi></mrow></math> collisions, while the background is smaller, and the upper limit of the CME signal is <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>15</mn><mo>%</mo></mrow></math> in the isobar collisions.</p>

China

Zilin Yuan

Anping Huang

Guannan Xie

Wen-Hao Zhou

Guo-Liang Ma

Mei Huang

Exploring the chiral magnetic effect in isobar collisions through chiral anomaly transport

Magnetic fields in heavy-ion collisions are pivotal and subject to diverse factors. In this study, we quantitatively investigate the impact of fluid vorticity on the evolution of magnetic fields in the 20%–50% centrality class in <math><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions, with collision energies of <math><mrow><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mspace></mspace><mo>(</mo><mn>7.7</mn><mo>,</mo><mn>14.5</mn><mo>,</mo><mn>19.6</mn><mo>,</mo><mn>27</mn><mo>,</mo><mn>39</mn><mo>,</mo><mn>62.4</mn><mo>,</mo><mn>200</mn><mo>)</mo><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>. Our results indicate that fluid vorticity leads to a delay in the evolution of the magnetic field, in which this effect becomes more pronounced as the collision energy decreases. Additionally, we have calculated the mean magnetic field values on the freeze-out hypersurface for various collision energies. Our simulation results align with the values inferred from experimental data of <math><mover><mi>Λ</mi><mo>¯</mo></mover><mo>−</mo><mi>Λ</mi></math>, within the error margins.

Canada

United States

Xiang-Yu Wu

Effect of vorticity on the dynamical magnetic fields in heavy-ion collisions

Built upon the state-of-the-art model a multiphase transport, we develop a new module of chiral anomaly transport (CAT) to trace the evolution of the initial topological charge of the gauge field created through sphaleron transition at finite temperature and the external magnetic field in heavy-ion collisions. The eventual experimental signals of the chiral magnetic effect (CME) have been measured. The CAT explicitly shows the generation and evolution of the charge separation, the signals of the CME through the CAT are quantitatively in agreement with the experimental measurements in <math><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions at <math><mrow><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV, and the centrality dependence of the CME fraction follows that of the fireball temperature. Our simulation supports the generation of the CME.

Evolution of topological charge through chiral anomaly transport

The magnetic fields in heavy-ion collisions are important ingredients for many interesting phenomena, such as the chiral magnetic effect, the chiral magnetic wave, the directed flow <math><msub><mi>v</mi><mn>1</mn></msub></math> of <math><msup><mi>D</mi><mn>0</mn></msup></math> mesons, and the splitting of the spin polarization of the <math><mi>Λ</mi><mo>/</mo><mover><mi>Λ</mi><mo>¯</mo></mover></math>. Quantitative studies of these phenomena, however, suffer from limited understanding of the dynamical evolution of these fields in the medium created by the collisions, which remains a critical and challenging problem. The initial magnetic fields from the colliding nuclei decay very fast in the vacuum but their lifetime could be extended through medium response due to electrically conducting quarks and antiquarks. Here we perform a detailed analysis of such medium effect on the dynamical magnetic fields by numerically solving Maxwell's equations concurrently with the expanding medium described by viscous hydrodynamics, under the assumption of negligible back reaction of the fields on the fluid evolution. Our results suggest a considerable enhancement of late time magnetic fields, the magnitude of which depends sensitively on the fireball expansion as well as the medium electric conductivity both before and during hydrodynamic stage.

Duan She

Shuzhe Shi

Jinfeng Liao

Dynamical magnetic fields in heavy-ion collisions

Gauge fields provide the fundamental interactions in the Standard Model of particle physics. Gauge field configurations with nontrivial topological windings are known to play crucial roles in many important phenomena, from matter-antimatter asymmetry of today’s universe to spontaneous chiral symmetry breaking in strong interaction. Their presence is, however, elusive for direct detection in experiments. Here we show that measurements of the chiral magnetic effect (CME) in heavy ion collisions can be used for accessing the topological fluctuations of the non-Abelian gauge fields in the quantum chromodynamics (QCD). To achieve this, we implemented a key ingredient, the stochastic dynamics of gauge field topological fluctuations, into a state-of-the-art framework for simulating the CME in these collisions. This new framework provides the necessary tool to quantify initial topological fluctuations from any definitive CME signal to be extracted from experimental data. It also reveals a universal scaling relation between initial topological fluctuations and particle multiplicity produced in the corresponding collision events.

Shu Lin

Xingyu Guo

Accessing topological fluctuations of gauge fields with the chiral magnetic effect

The global polarization of <math><mi>Λ</mi><mo>/</mo><mover><mi>Λ</mi><mo>¯</mo></mover></math> and the splitting between them induced by rotation and magnetic field has been investigated in a dynamical quark model by taking into account the axial-vector interaction and the anomalous magnetic moment of quarks. It is found that the rotation leads to the spin polarization of quarks and antiquarks with the same sign, while the magnetic field leads to the opposite sign, which corresponds to the <math><mover><mi>Λ</mi><mo>¯</mo></mover><mo>−</mo><mi>Λ</mi></math> polarization splitting. The combination of the two effects leads to perfect agreement with experimental data. Quantitatively, the axial-vector interaction contributes 30% of the global polarization and the anomalous magnetic moment of quarks contributes 40% to the splitting of <math><mover><mi>Λ</mi><mo>¯</mo></mover><mo>−</mo><mi>Λ</mi></math> polarization. However, at <math><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>≤</mo><mn>7.7</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, it still remains a challenge to reach enough magnitude of the magnetic field at freeze-out.

Kun Xu

Fan Lin

<math><mi>Λ</mi><mo>/</mo><mover><mi>Λ</mi><mo>¯</mo></mover></math> polarization and splitting induced by rotation and magnetic field

We investigate the rotating quark matter in the three-flavor Nambu–Jona-Lasinio (NJL) model. The chiral condensation, spin polarization, and number susceptibility of the light and strange quarks are carefully studied at finite temperatures without or with finite chemical potential in this model. We find that the rotation suppresses the chiral condensation and enhances the first-order quark spin polarization, however for the second-order quark spin polarization and quark number susceptibility the effect is complicated and interesting. When extending to the situation with finite chemical potential, we find the angular velocity also plays a crucial role, at small angular velocity the chemical potential enhances the susceptibility, however in the middle region of angular velocity the effect of the chemical potential is suppressed by the angular velocity and susceptibility can be changed considerably, it can be observed that at very low temperature in the presence of quark chemical potential the quark number susceptibility has two maxima with increasing angular velocity. Furthermore, it is found that at sufficiently large angular velocity the contributions played by the light quark and the strange quark to these phenomena are almost equal. We also discuss the chiral phase transition of rotating quark matter in the three-flavor NJL model. We expect these studies to be used to understand the chiral symmetry breaking and restoration as well as probe the QCD phase transition.

Fei Sun

Properties of strange quark matter under strong rotation

In this work, we study the relativistic quantum kinetic equations in <math><mn>2</mn><mo>+</mo><mn>1</mn></math> dimensions from Wigner function formalism by carrying out a systematic semiclassical expansion up to <math><mi>ℏ</mi></math> order. The derived equations allow us to explore interesting transport phenomena in <math><mn>2</mn><mo>+</mo><mn>1</mn></math> dimensions. Within this framework, the parity-odd transport current induced by the external electromagnetic field is self-consistently derived. We also examine the dynamical mass generation by implementing four-fermion interaction with mean-field approximation. In this case, a new kind of transport current is found to be induced by the gradient of the mean-field condensate. Finally, we also utilize this framework to study the dynamical mass generation in an external magnetic field for the (<math><mrow><mn>2</mn><mo>+</mo><mn>1</mn></mrow></math>)-dimensional system under equilibrium.

Xianglei Zhu

Lianyi He

Pengfei Zhuang

Quantum kinetic equation and dynamical mass generation in <math><mrow><mn>2</mn><mo>+</mo><mn>1</mn></mrow></math> dimensions

According to the Kubo formulas, we employ the (<math><mrow><mn>3</mn><mo>+</mo><mn>1</mn></mrow></math>)-d parton cascade, Boltzmann approach of multiparton scatterings to calculate the anisotropic transport coefficients (shear viscosity and electric conductivity) for an ultrarelativistic Boltzmann gas in the presence of a magnetic field. The results are compared with those recently obtained by using the Grad’s approximation. We find good agreements between both results, which confirms the general use of the derived Kubo formulas for calculating the anisotropic transport coefficients of quark-gluon plasma in a magnetic field.

Zhengyu Chen

Germany

Carsten Greiner

Zhe Xu

Calculation of anisotropic transport coefficients for an ultrarelativistic Boltzmann gas in a magnetic field within a kinetic approach

Recently, there has been significant interest in understanding the macroscopic quantum transport in a many-body system of chiral fermions. A natural framework for describing such a system that is generally out of equilibrium is the transport equation for its phase space distribution function. In this paper, we obtain a complete solution of the covariant chiral transport for massless fermions, by starting from the general Wigner function formalism and carrying out a complete and consistent semiclassical expansion up to <math><mrow><mover><mrow><mi>O</mi></mrow><mrow><mo>^</mo></mrow></mover><mo>(</mo><mo>ℏ</mo><mo>)</mo></mrow></math> order. In particular, we clarify certain subtle and confusing issues surrounding the Lorentz noninvariance and frame dependence associated with the three-dimensional chiral kinetic theory. We prove that such frame dependence is uniquely and completely fixed by an unambiguous definition of the <math><mrow><mover><mrow><mi>O</mi></mrow><mrow><mo>^</mo></mrow></mover><mo>(</mo><mo>ℏ</mo><mo>)</mo></mrow></math> correction to the distribution function in each reference frame.