Lawrence Livermore National Laboratory, Livermore, California, USA.
Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic.
Phys Rev Lett. 2013 Nov 27;111(22):222301. doi: 10.1103/PhysRevLett.111.222301. Epub 2013 Nov 25.
The ALICE measurement of K(S)(0) and Λ production at midrapidity in Pb-Pb collisions at √(s(NN))=2.76 TeV is presented. The transverse momentum (p(T)) spectra are shown for several collision centrality intervals and in the p(T) range from 0.4 GeV/c (0.6 GeV/c for Λ) to 12 GeV/c. The p(T) dependence of the Λ/K(S)(0) ratios exhibits maxima in the vicinity of 3 GeV/c, and the positions of the maxima shift towards higher p(T) with increasing collision centrality. The magnitude of these maxima increases by almost a factor of three between most peripheral and most central Pb-Pb collisions. This baryon excess at intermediate p(T) is not observed in pp interactions at √s=0.9 TeV and at √s=7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured p(T) spectra above 2 GeV/c progressively decouple from hydrodynamical-model calculations. For higher values of p(T), models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the p(T) dependence of the Λ/K(S)(0) ratio.
ALICE 实验测量了在质心能量为 √(s(NN))=2.76 TeV 的 Pb-Pb 碰撞中 K(S)(0) 和 Λ 的产量。展示了几个碰撞中心度间隔和在横动量 (p(T)) 范围从 0.4 GeV/c（对于 Λ 为 0.6 GeV/c）到 12 GeV/c 的 p(T)谱。Λ/K(S)(0) 比在大约 3 GeV/c 附近表现出最大值，并且随着碰撞中心度的增加，最大值的位置向更高的 p(T)移动。在最外围和最中心的 Pb-Pb 碰撞之间，这些最大值的幅度增加了近三倍。在 √s=0.9 TeV 和 √s=7 TeV 的 pp 相互作用中，没有观察到中间 p(T)处的这种重子过剩。从径向流定性上预计重离子碰撞中的重子增强。然而，在高于 2 GeV/c 的测量 p(T)谱与流体力学模型计算逐渐脱钩。对于更高的 p(T)值，包含介质对碎裂和强子化过程影响的模型定性地描述了 Λ/K(S)(0) 比随 p(T)的依赖关系。
