大型强子对撞机上p-Pb碰撞中的强子“流”？
Hadronic "flow" in p--Pb collisions at the Large Hadron Collider?
摘要：
利用超相对论量子分子动力学（UrQMD）模型，研究了$\sqrt{s_{_{\rm NN}}}=5.02$ TeV下p-Pb碰撞中的方位角关联.与实验数据的比较表明，UrQMD不能再现2粒子和4粒子累积量对多重数的依赖性，尤其是在高多重数事件中$c_{2}\{4\}$由正值到负值的转变，这已被作为p-Pb碰撞集体性的实验证据.同时，UrQMD不能定性地描述所有带电强子在不同多重数下的微分椭圆流$v_{2}(p_{\rm T})$.这些差异表明，模拟的p-Pb强子系统不能产生足够的集体流，伴随的强子发射主要受非流效应的影响.然而，特征$v_{2}(p_{\rm T})$质量排序的π介子，K介子和质子中观察到UrQMD，这是强子相互作用的结果，并不一定与强流体般的膨胀。
英文摘要：
Using the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model, we investigate azimuthal correlations in p--Pb collisions at $\sqrt{s_{_{\rm NN}}}=5.02$ TeV. Comparison with the experimental data shows that UrQMD can not reproduce the multiplicity dependence of 2- and 4-particle cumulants, especially the transition from positive to negative values of $c_{2}\{4\}$ in high multiplicity events, which has been taken as experimental evidence of collectivity in p--Pb collisions. Meanwhile, UrQMD can not qualitatively describe the differential elliptic flow, $v_{2}(p_{\rm T})$, of all charged hadrons at various multiplicity classes. These discrepancies show that the simulated hadronic p--Pb systems can not generate enough collective flow as observed in experiment, the associated hadron emissions are largely influenced by non-flow effects. However, the characteristic $v_{2}(p_{\rm T})$ mass-ordering of pions, kaons and protons is observed in UrQMD, which is the consequence of hadronic interactions and not necessarily associated with strong fluid-like expansions.
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