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arXiv 1703.05947hep-phnucl-th
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手征有效模型中的重子数涨落及其唯象意义

Baryon number fluctuations in chiral effective models and their phenomenological implications

Gabor Almasi, Bengt Friman, Krzysztof Redlich

备注：
15 pages, 13 figures
发表信息：
Phys. Rev. D 96, 014027 (2017)
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摘要：

本文研究了在有限温度和重子密度下介质中手征恢复跃迁的重子数涨落的临界性质。量子色动力学（QCD）的手征动力学模型采用Polykov圈扩展的夸克-介子拉格朗日量，其中包括夸克与矢量介子和时间规范场的耦合。泛函重整化群被用来正确地解释相边界处的$O(4)$临界性。我们着重研究了在相界附近的净重子数累积量$χ_B^n$，对于${1\leq n\leq 6}$，比值的性质和系统学。结果的背景下，最近的实验数据的STAR合作的波动的净质子数在RHIC的重离子碰撞。我们表明，模型的累积比的能量依赖性的结果是在良好的整体协议的数据，有一个例外。在质心能量低于${19.6\;\mathrm{GeV}}$，我们发现，测量的四阶累积量偏离模型的结果，其中包括预期的$O(4)$和$Z(2)$临界。我们评估模型假设的影响，特别是排斥矢量的相互作用，这是用来修改模型中的关键端点的位置，累积量的比率。最后，我们讨论了一种可能性，以测试在何种程度上的波动的影响，通过比较一定比例的累积量的非平衡动力学。

英文摘要：

We study the critical properties of net-baryon-number fluctuations at the chiral restoration transition in a medium at finite temperature and net baryon density. The chiral dynamics of quantum chromodynamics (QCD) is modeled by the Polykov-loop extended Quark-Meson Lagrangian, that includes the coupling of quarks to vector meson and temporal gauge fields. The Functional Renormalization Group is employed to properly account for the $O(4)$ criticality at the phase boundary. We focus on the properties and systematics of ratios of the net-baryon-number cumulants $χ_B^n$, for ${1\leq n\leq 6}$, near the phase boundary. The results are presented in the context of the recent experimental data of the STAR Collaboration on fluctuations of the net proton number in heavy ion collisions at RHIC. We show that the model results for the energy dependence of the cumulant ratios are in good overall agreement with the data, with one exception. At center-of-mass energies below ${19.6\;\mathrm{GeV}}$, we find that the measured fourth-order cumulant deviates considerably from the model results, which incorporate the expected $O(4)$ and $Z(2)$ criticality. We assess the influence of model assumptions and in particular of repulsive vector-interactions, which are used to modify the location of the critical endpoint in the model, on the cumulants ratios. Finally, we discuss a possibility to test to what extent the fluctuations are affected by nonequilibrium dynamics by comparing certain ratios of cumulants.

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