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 le...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.展开更多
There must be electromagnetic fields created during high-energy heavy-ion collisions.Although the electromagnetic field may become weak with the evolution of the quark-gluon plasma(QGP),compared to the energy scales o...There must be electromagnetic fields created during high-energy heavy-ion collisions.Although the electromagnetic field may become weak with the evolution of the quark-gluon plasma(QGP),compared to the energy scales of the strong interaction,they are potentially important to some electromagnetic probes.In this work,we propose the coupled effect of the weak magnetic field and the longitudinal dynamics of the background medium for the first time.We demonstrate that the induced photon spectrum can be highly azimuthally anisotropic when the quarkgluon plasma is in the presence of a weak external magnetic field.On the other hand,the weak magnetic photon emission from quark-gluon plasma only leads to a small correction to the photon production rate.After hydrodynamic evolution with a tilted fireball configuration,the experimentally measured direct photon elliptic flow is well reproduced.Meanwhile,the used time-averaged magnetic field in the hydrodynamic stage is found no larger than a few percent of the pion mass square.展开更多
this work,the polarization effects of a strongly magnetized quark-gluon plasma are studied at finite temperature.It is found that a background magnetic field can have a strong effect on the photon and dilepton emissio...this work,the polarization effects of a strongly magnetized quark-gluon plasma are studied at finite temperature.It is found that a background magnetic field can have a strong effect on the photon and dilepton emission rates.It affects not only the total rate but also the angular dependence.In particular,the Landau-level quantization leads to a nontrivial momentum dependence of the photon/dilepton anisotropic flow coefficient on transverse momentum.In the case of photon emission,nonzero coefficients v_(n)(with even n)have opposite signs at small and large values of the transverse momentum.Additionally,the v_(n) signs alternate with increasing vn,and their approximate values decrease as 1/n^(2) in magnitude.The anisotropy of dilepton emission is well-pronounced only at large transverse momenta and small invariant masses.The corresponding Un coefficients are of the same magnitude and show a similar sign-alternative pattern with increasing n as in the photon emission.It is proposed that the anisotropy of the photon and dilepton emission may serve as indirect measurements of the magnetic field.展开更多
基金supported in part by the National Natural Science Foundation of China(No.11747312)the U.S.Department of Energy(No.de-sc0012910)
文摘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.
文摘There must be electromagnetic fields created during high-energy heavy-ion collisions.Although the electromagnetic field may become weak with the evolution of the quark-gluon plasma(QGP),compared to the energy scales of the strong interaction,they are potentially important to some electromagnetic probes.In this work,we propose the coupled effect of the weak magnetic field and the longitudinal dynamics of the background medium for the first time.We demonstrate that the induced photon spectrum can be highly azimuthally anisotropic when the quarkgluon plasma is in the presence of a weak external magnetic field.On the other hand,the weak magnetic photon emission from quark-gluon plasma only leads to a small correction to the photon production rate.After hydrodynamic evolution with a tilted fireball configuration,the experimentally measured direct photon elliptic flow is well reproduced.Meanwhile,the used time-averaged magnetic field in the hydrodynamic stage is found no larger than a few percent of the pion mass square.
文摘this work,the polarization effects of a strongly magnetized quark-gluon plasma are studied at finite temperature.It is found that a background magnetic field can have a strong effect on the photon and dilepton emission rates.It affects not only the total rate but also the angular dependence.In particular,the Landau-level quantization leads to a nontrivial momentum dependence of the photon/dilepton anisotropic flow coefficient on transverse momentum.In the case of photon emission,nonzero coefficients v_(n)(with even n)have opposite signs at small and large values of the transverse momentum.Additionally,the v_(n) signs alternate with increasing vn,and their approximate values decrease as 1/n^(2) in magnitude.The anisotropy of dilepton emission is well-pronounced only at large transverse momenta and small invariant masses.The corresponding Un coefficients are of the same magnitude and show a similar sign-alternative pattern with increasing n as in the photon emission.It is proposed that the anisotropy of the photon and dilepton emission may serve as indirect measurements of the magnetic field.
