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.     

Energy Dependence of String Fragmentation Function and φ Meson Production

The φ meson productions in Au+Au and/or Pb+Pb collisions at AGS, SPS, RHIC, and LHC energies have been studied systematically with a hadron and string cascade model LUCIAE. After considering the energy dependence of the model parameter α in string fragmentation function and adjusting it to the experimental data of charged multiplicity to a certain extent, the model predictions for φ meson yield, rapidity, and transverse mass distributions are compatible with the experimental data at AGS, SPS and RHIC energies. A calculation for Pb+Pb collisions at LHC energy is given as well. The obtained fractional variable in string fragmentation function shows a saturation in energy dependence. It is discussed that the saturation of fractional variable in string fragmentation function might be a qualitative representation of the energy dependence of nuclear transparency.     

Chiral electric field in relativistic heavy-ion collisions at energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider

It has been proposed that electric fields may lead to chiral separation in quark-gluon plasma(QGP).This is called the chiral electric separation effect.The strong electromagnetic field and the QCD vacuum can both be completely produced in off-central nuclear-nuclear collision.We use the Woods-Saxon nucleon distribution to calculate the electric field distributions of off-central collisions.The chiral electric field spatial distribution at Relativistic Heavy-Ion Collider(RHIC) and Large Hadron Collider(LHC) energy regions are systematically studied in this paper.The dependence of the electric field produced by the thermal quark in the central position with different impact parameters on the proper time with different collision energies in the RHIC and LHC energy regions are studied in this paper.     

The chiral magnetic effect: Beam-energy and system-size dependence

We consider the energy dependence of the local P and CP violation in AuAu and CuCu collisions over a large energy range within a simple phenomenological model. It is expected that at LHC the chiral magnetic effect will be about 20 times weaker than at RHIC. At lower energy range this effect should vanish sharply at energy somewhere above the top SPS one. To elucidate CME background effects a transport model including magnetic field evolution is put forward.     

相对论重离子碰撞手征电荷分离效应的研究

相对论重离子碰撞的拓扑荷作用破坏作用平面两侧不同手征性的夸克数目的平衡,从而引起P和CP破坏特征。本工作主要分析RHIC和LHC能区的手征电荷分离作用,分析手征电荷分离随碰撞中心度、碰撞能量和核屏蔽等依赖关系。并未发现手征电荷分离效应与碰撞能量大小有非常紧密的依赖关系,但发现核屏蔽效应对手征电荷分离有重要的影响,与不考虑屏蔽效应相比,考虑屏蔽效应会使手征分离效应明显压低,由于屏蔽效应出现,使得a₊₊（a_--）的分布与a_+-（a_-+）分布并不对称。并且还发现手征分离效应主要发生在碰撞参量较大的周边碰撞,越接近中心碰撞,手征分离效应几乎可以忽略。The topological charge interactions in relativistic heavy ion collisions cause quark chirality imbalance, resulting in charge separation under the strong magnetic field and local P and CP violation. In this paper, the chiral charge separation at RHIC and LHC energies is systematically analyzed as functions of the collision centrality, the collision energy and the nuclear shielding factor. It is found that there is not a very close dependence of the chiral charge separation effect on the collision energies, but that has an important dependence on nuclear shielding factor. Compared with the non-shielding effect, the shielding effect can reduce the chiral separation effect obviously. Due to the shielding effect, the distribution of a₊₊(a_--) and the distribution of a_+-(a_-+) are asymmetric. One also finds that chiral separation effect, which is almost negligible when more close to the central collision, occurs mainly in the peripheral collision for larger impact parameter.     

Open charm and beauty at ultrarelativistic heavy ion colliders

Important goals of BNL RHIC and CERN LHC experiments with ion beams include the creation and study of new forms of matter, such as the quark gluon plasma. Heavy quark production and attenuation provide unique tomographic probes of that matter. We predict the suppression pattern of open charm and beauty in Au+Au collisions at RHIC and LHC energies based on the DGLV formalism of radiative energy loss. A cancellation between effects due to the sqrt[s] energy dependence of the high p(T) slope and heavy quark energy loss is predicted to lead to surprising similarity of heavy quark suppression at RHIC and LHC.     

高能核-核碰撞中直接光子各向异性的数值模拟研(英文)

通过计算给出了在LHC能区非对心核 核碰撞中由椭圆流ν₂ 表示的高横动量直接光子的方位角不对称性。该高横动量光子是由喷注与热密介质相互作用而辐射出来的。光子椭圆流与强子椭圆流ν₂ 相差π/2的相位, 是直接光子椭圆流中负值的来源。同时, 计算表明LHC能区直接光子ν₂随粒子横动量p_T的变化趋势与RHIC上的实验结果一致, 但LHC能区较RHIC能区有更低的直接光子流ν₂ 值, 且ν₂ 值由负到正对应的转换p_T值更高。这表明在LHC能区喷注淬火效应更为明显, 表面发射的直接光子对光子椭圆流的贡献份额增强。The azimuthal anisotropy of high p_T direct photons is investigated by using the coefficient of elliptic flow ν₂ in non-central nucleus-nucleus collision at LHC energies. These photons come from radiation induced by the interaction between jet and hot/dense medium. The azimuthal anisotropy of high p_T direct photons is investigated by using the coefficient of elliptic flow ν₂ in non-central nucleus-nucleus collision at LHC energies. These photons come There is π/2 difference between direct photons and hadrons for the azimuthal elliptic flow ν₂. Such photons are the main source of the negative part of ν₂ for direct photons. The dependence of the direct photon ν₂ on the transverse momentum p_T at LHC energy is found to be consistent with the experimental results at RHIC energy. Furthermore, we find that the value of the direct photon ν₂ at LHC energy is smaller than that at RHIC energy. The value of the transverse momentum at which the direct photon ν₂ changes from negative value to positive at LHC is higher than that at RHIC. It’sfound the enhanced jet quenching effect and enhanced contribution for the elliptic flow ν₂ of the direct photons emitted from surface at LHC energy.     

xF (or y)-Dependence of Nuclear Absorption and Energy Loss Effects onJ/ψ Production

By means of the nuclear parton distribution studied only with lepton deep-inelastic scattering experimental data, the J/ψ ``normal nuclear absorption' and energy loss effects are studied in a Glauber formalism at HERA and RHIC energies. Assuming that the absorption cross section σ_abs increases with thecharmonium-nucleon center of mass energy, the results reveal a significant dependence of the σ_abs on rapidity y at RHIC energies. The initial-state energy loss effect, which is found important only at HERA energies, is also considered, and its influence should be eliminated when we studied the absorption effect at low collision energies. Finally, we also present the theoretical prediction for LHC.     

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.     

Using dileptons to probe the color glass condensate

The rapidity and transverse momentum dependence of the nuclear modification ratio for dilepton production at RHIC and LHC is presented, calculated in the color glass condensate (CGC) framework. The transverse momentum ratio is compared for two distinct dilepton mass values and a suppression of the Cronin peak is verified even for large mass. The nuclear modification ratio suppression in the dilepton rapidity spectra, as obtained experimentally for hadrons at RHIC, is verified for LHC energies at large transverse momentum, although not present at RHIC energies. The ratio between LHC and RHIC nuclear modification ratios is evaluated in the CGC, showing the large saturation effects at LHC compared with the RHIC results. These results consolidate the dilepton as a most suitable observable to investigate the QCD high density approaches.     

J/ψ-N center of mass energy dependence of nuclear absorption effect on J/ψ production

In this paper, the J/ψ nuclear absorption effect is studied at RHIC and LHC energies with the EKS98 shadowing parameterizations. By assuming that the J/ψ absorption cross section, σ abs , increases with the charmonium-nucleon (J/ψ-N) center of mass energy, s J/ψN , it is found that σ abs should depend on x F (or y) at a certain center of mass energy per nucleon pair,s , especially at LHC energies. The theoretical results with the x F (or y)-dependence of the absorption effect are in good agreement with the experiment data from PHENIX in d-Au collisions and the predicted results will be examined by the forthcoming experimental data from LHC in d-Pb collisions. Finally, we also present baseline calculations of cold nuclear matter effects on J/ψ production in nucleus-nucleus (A-A) collisions and find that the x F (or y)-dependence of absorption effect is very small at both RHIC and LHC energies in A-A collisions.     

Beam-energy and system-size dependence of the CME

The energy dependence of the local and violation in Au + Au and Cu + Cu collisions in a large energy range is estimated within a simple phenomenological model. It is expected that at LHC the Chiral Magnetic effect (CME) will be about 20 times weaker than at RHIC. In the lower energy range this effect should vanish sharply at energy somewhere above the top SPS one. To elucidate CME background effects a transport model including magnetic field evolution is put forward.     

Hydrokinetic predictions for femtoscopy scales in A + A collisions in the light of recent ALICE LHC results

A study of energy behavior of the pion spectra and interferometry scales is carried out for the top SPS, RHIC and for LHC energies within the hydrokinetic approach. The main mechanisms that lead to the paradoxical, at first sight, dependence of the interferometry scales with an energy growth, in particular, a decrease R _out/R _side ratio, are exposed. The hydrokinetic predictions for the HBT radii at LHC energies are compared with the recent results of the ALICE experiment.     

J/psi production in quark-gluon plasma

We study J/psi production at RHIC and LHC energies with both initial production at energies reached and the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC) with regeneration. We solve the coupled set of transport equations for the J/psi distribution in phase space and the hydrodynamic equation for evolution of quark-gluon plasma. At RHIC, continuous regeneration is crucial for the J/psi momentum distribution while the elliptic flow is still dominated by initial production. At energies reached at the LHC energy, almost all the initially created J/psis are dissociated in the medium and regeneration dominates the J/psi properties.     

PACIAE model capability in describing net proton moments

PACIAE 2.0, a parton and hadron cascade model, is employed to investigate the dependence of the moments of net proton event distributions on reaction energies varying from RHIC to LHC energy in p + p collisions. It is found that net proton moments and moment products are sensitive to the collision energy except the moment product k?? ² which is almost independent of the collision energy. The PACIAE results are in line with experimental data.     

Effect of Giant Resonances on Fluctuations of Electromagnetic Fields in Heavy Ion Collisions

JETP Letters - We perform quantum calculations of fluctuations of the electromagnetic fields in AA collisions at RHIC and LHC energies. Calculations are performed with the help of the...     

Chemical potential dependence of particle ratios within a unified thermal approach

A unified statistical thermal freeze-out model (USTFM) is used to study the chemical potential dependence of identified particle ratios at mid-rapidity in heavy-ion collisions. We successfully reproduce the experimental data ranging from SPS energies to LHC energies, suggesting the statistical nature of the particle production in these collisions and hence the validity of our approach. The behavior of the freeze-out temperature is studied with respect to chemical potential. The freeze-out temperature is found to be universal at the RHIC and LHC and is close to the QCD predicted phase transition temperature, suggesting that the chemical freeze-out occurs soon after the hadronization takes place.     

Tagged jets and jet reconstruction as a probe of the quark-gluon plasma

The large center-of-mass energies available to the heavy-ion program at the LHC and recent experimental advances at RHIC will enable QCD matter at very high temperatures and energy densities, that is, the quark-gluon plasma (QGP), to be probed in unprecedented ways. Fully-reconstructed inclusive jets and the away-side hadron showers associated with electroweak bosons, that is, tagged jets, are among these exciting new probes. Full jet reconstruction provides an experimental window into the mechanisms of quark and gluon dynamics in the QGP which is not accessible via leading particles and leading particle correlations. Theoretical advances in these exciting new fields of research can help resolve some of the most controversial points in heavy ion physics today such as the significance of the radiative, collisional and dissociative processes in the QGP and the applicability of strong versus weak coupling regimes to describe jet production and propagation. In this proceedings, I will present results on the production and subsequent suppression of high energy jets tagged with Z bosons in relativistic heavy-ion collisions at RHIC and LHC energies using the Gyulassy-Levai-Vitev (GLV) parton energy loss approach.     

Production of secondaries in high-energy <Emphasis Type="Italic">d</Emphasis>+Au collisions

In the framework of the quark–gluon string model we calculate the inclusive spectra of secondaries produced in d+Au collisions at intermediate (CERN SPS) and at much higher (RHIC) energies. The results of numerical calculations at intermediate energies are in reasonable agreement with the data. At RHIC energies numerically large inelastic screening corrections (percolation effects) should be accounted for in the calculations. We extract these effects from the existing experimental data of RHIC on minimum-bias and central d+Au collisions. The predictions for p+Au interactions at LHC energy are also given.     

Hadronic energy density in the dual parton model with formation zone intranuclear cascade

We study the evolution of the hadronic energy and particle density during central nucleus-nucleus collisions at various energies with a Monte Carlo version of the dual parton model. We find at RHIC and at LHC energies energy densities well in the range where the formation of quark gluon plasma is expected.