解码A+A碰撞中的QCD临界行为
Decoding the QCD critical behaviour in A+A collisions
摘要：
在CERN SPS对核碰撞中QCD临界点的系统研究中，发现在最大SPS能量下，在中心Si+Si碰撞的冻结状态下的不透明度测量为我们提供了相当大的临界波动的指示。此外，相当近，在Ar+Sc反应的初步数据中追踪到在（大约）相同能量下10-20%最中心碰撞的较弱效应。然而，分析中的不确定性和实验事件统计的局限性使得对上述测量（NA 49，NA 61/SHINE）的解释相当不确定，需要进一步的唯象研究，并使用补充工具和理论思想。为此，在目前的工作中，我们在模型独立分析方案（AMIAS）中采用了非线性技术，这是数据科学的一种新方法[arXiv：1205.6505]，以便为幂律的参数，特别是相关的幂律指数（非线性指数）$ϕ_2$产生无偏结果。利用不同边缘的数据集，我们还研究了$ϕ_2$ -值对受伤核子数的依赖性，以揭示临界点的接近。利用这些发现和Ising-QCD配分函数的帮助，讨论了SPS不透明度测量的解释及其与临界区的联系。
英文摘要：
In a systematic search for the QCD critical point in nuclear collisions, at the CERN SPS, it was found that intermittency measurements in the freeze-out state of central Si+Si collisions, at the maximum SPS energy, provide us with an indication of sizeable critical fluctuations. Also, rather recently, a weaker effect was traced in preliminary data of the Ar+Sc reaction for 10-20% most central collisions at (approximately) the same energy. However, the uncertainties in the analysis and the limitations of the experimental event statistics make the interpretation of the above measurements (NA49, NA61/SHINE) rather inconclusive, inviting for a further, phenomenological investigation with complementary tools and theoretical ideas. To this end, in the present work, we employ intermittency techniques within a model-independent analysis scheme (AMIAS), a novel method from Data Science [arXiv:1205.6505], in order to produce unbiased results for the parameters of the power-laws and in particular for the associated power-law exponent (intermittency index) $ϕ_2$. Using data-sets at different peripheralities, we also study the dependence of the $ϕ_2$-value on the number of wounded nucleons, in order to uncover the approach to the critical point. With these findings and the help of Ising-QCD partition function, the interpretation of SPS intermittency measurements and their links to the critical region, are discussed.
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