Magnetic effects in heavy-ion collisions at intermediate energies
Magnetic effects in heavy-ion collisions at intermediate energies
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DOI：
10.1103/physrevc.84.064605
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发表时间：
2011-07
影响因子：
3.1
通讯作者：
L. Ou;Bao-An Li
中科院分区：
文献类型：
--
作者：
L. Ou;Bao-An Li
在同位旋相关的Boltzmann-Uhling-Uhlenbeck输运模型IBUU 11下，研究了束流能量为200 - 2000 MeV/核子的重离子反应中内电磁场的时间演化和空间分布.虽然磁场可以达到约$7\times10 ^{16}$ G，这是显着高于估计的磁星表面磁场（$\sim 10^{15}$ G），它几乎没有影响核子的可观测性，因为洛伦兹力通常比核力弱得多。然而，非常有趣的是，由类似弹丸（类似靶）的旁观者产生的磁场对正/负π介子在向前（向后）的快速性上有很强的聚焦/发散效应。因此，作为快度函数的微分$\pi^-/\pi^+$比值会被磁场显著改变，而正负π介子的总多重数保持不变。当束流能量大于1 GeV/核子时，当总$\pi^-$与$\pi^+$的积分比值不变化时，微分$\pi^-/\pi^+$比值对核对称能E_{\rm{sym}}（\rho）$的密度依赖性敏感。我们的研究结果表明，磁效应应仔细考虑在未来的研究中使用的微分$\pi^-/\pi^+$的比例作为探针的$E_{\rm{sym}}（\rho）$在超饱和密度。
The time-evolution and space-distribution of internal electromagnetic fields in heavy-ion reactions at beam energies between 200 and 2000 MeV/nucleon are studied within an Isospin-dependent Boltzmann-Uhling-Uhlenbeck transport model IBUU11. While the magnetic field can reach about $7\times 10^{16}$ G which is significantly higher than the estimated surface magnetic field ($\sim 10^{15}$ G) of magnetars, it has almost no effect on nucleon observables as the Lorentz force is normally much weaker than the nuclear force. Very interestingly, however, the magnetic field generated by the projectile-like (target-like) spectator has a strong focusing/diverging effect on positive/negative pions at forward (backward) rapidities. Consequently, the differential $\pi^-/\pi^+$ ratio as a function of rapidity is significantly altered by the magnetic field while the total multiplicities of both positive and negative pions remain about the same. At beam energies above about 1 GeV/nucleon, while the integrated ratio of total $\pi^-$ to $\pi^+$ multiplicities is not, the differential $\pi^-/\pi^+$ ratio is sensitive to the density dependence of nuclear symmetry energy $E_{\rm{sym}}(\rho)$. Our findings suggest that magnetic effects should be carefully considered in future studies of using the differential $\pi^-/\pi^+$ ratio as a probe of the $E_{\rm{sym}}(\rho)$ at supra-saturation densities.