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arXiv 1607.02891nucl-th
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感生电场对重离子碰撞中π^{-}/π^{+}比的影响

Effects of an induced electric field on π^{-}/π^{+} ratio in heavy-ion collisions

Gao-Feng Wei, Shi-Hai Dong, Xin-Wei Cao, Yun-Liang Zhang

备注：
7 pages, 15 figures, Accepted for publication in Physical Review C
发表信息：
Physical Review C 94, 014605 (2016)
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摘要：

利用一个与同位旋和动量相关的输运模型，研究了能量为400和1500 MeV/核子的中心-周边重离子碰撞中，可变磁场诱导的电场对π^{-}/π^{+}比值的影响.结果表明，在400 MeV/核子的低能量和1500 MeV/核子的高能量下，虽然感生电场对$π^{-}$和$π^{+}$介子的多重数没有影响，但感生电场降低了它们的多重数（增强）$π^{-}$的释放（$π^{+}$）介子在中快度，但增强（减少）$π^{-}$的发射（$π^{+}$）由于快速瞬态变化的磁场，在较低的束流能量下，特别是对于更外围的碰撞，向前和向后的介子快速在较低的束能量下，更多的外围碰撞和更长的反应持续时间。这些结果表明，总的π^{-}/π^{+}比仍然是一个精确可靠的探针的对称性能量在较低和较高的光束能量，但人们应该考虑感应电场时，使用微分π^{-}/π^{+}比探测对称性能量，特别是对于较低的光束能量和更多的周边碰撞。最后，基于不同快度下的π^{-}/π^{+}比值的相对抑制因子可以最大化诱导电场对微分π^{-}/π^{+}比值的影响，而最小化重离子碰撞中某些不确定因素的影响，因此可以作为探测重离子碰撞中诱导电场的有效工具.

英文摘要：

Using an isospin- and momentum-dependent transport model, we examine the effects of an electric field induced by a variable magnetic field on the π^{-}/π^{+} ratio in central to peripheral heavy-ion collisions at beam energies of 400 and 1500MeV/nucleon. It is shown that while the induced electric field does not affect the total multiplicities of both $π^{-}$ and $π^{+}$ mesons at both the lower beam energy of 400MeV/nucleon and the higher beam energy of 1500MeV/nucleon, it reduces (enhances) the emission of $π^{-}$ ($π^{+}$) mesons in midrapidity, but enhances (reduces) the emission of $π^{-}$ ($π^{+}$) mesons in forward and backward rapidities especially for the more peripheral collisions at the lower beam energy because of the rapidly transient variable magnetic field at more peripheral collisions and longer reaction duration time at the lower beam energy. These findings indicate that the total π^{-}/π^{+} ratio is still a precisely reliable probe of symmetry energy at both the lower and higher beam energies, but one should consider the induced electric field when using the differential π^{-}/π^{+} ratio to probe the symmetry energy especially for the lower beam energy and more peripheral collisions. Finally, the relative suppression factor based on the ratio of π^{-}/π^{+} in different rapidities is proposed to be an effective probe of the induced electric field generated in heavy-ion collisions due to its maximizing effects of induced electric fields on the differential π^{-}/π^{+} ratio but minimizing effects of some uncertainty factors in heavy-ion collisions.

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