Title: Phenomenological study of the angle between jet axes in heavy-ion collisions Show Chinese title

Title: 重离子碰撞中喷流轴夹角的唯象研究

Abstract: This paper presents a phenomenological study on the angle between the Standard and the Winner-Take-All (WTA) jet axes ($\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$) in high-energy nuclear collisions. The $p$+$p$ baseline is provided by the Pythia8 event generator. The in-medium jet propagation is simulated by the linear Boltzmann transport (LBT) model, which considers both the elastic and inelastic jet-medium interactions. Our theoretical results calculated by the LBT model show that the $\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$ distribution in Pb+Pb at $\sqrt{s}=5.02$ TeV is narrower than that in $p$+$p$, which agrees well with the recent ALICE measurements. The narrowing of $\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$ seems to violate the $p_T$-broadening nature of the jet quenching effect, usually explained by the influence of "selection bias". However, the physical details still need to be fully understood. Utilizing a matching-jet method to track the jet evolution in the QGP to remove the selection bias in the Monte Carlo simulations, we observe that the $\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$ distribution becomes broader due to the jet-medium interactions. At the same time, by rescaling the quark/gluon-jet fractions in Pb+Pb collisions to be the same as that in $p$+$p$, we find that the fraction change may not significantly influence the modification pattern of jet $\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$. On the other hand, the selected jet sample in A+A collisions has a significantly narrower initial $\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$ distribution than the $p$+$p$ baseline, and such a biased comparison between $p$+$p$ and A+A conceals the actual jet-broadening effect in the experimental measurements. The investigations presented in this paper will deepen our understanding of the relationship between the actual intra-jet modifications in the QGP and the experimental observations. Show Chinese abstract

Abstract: 本文介绍了在高能核碰撞中标准喷流轴和Winner-Take-All (WTA) 喷流轴之间的夹角（$\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$）的唯象研究。由Pythia8事件生成器提供的基准线是 $p$+$p$。通过线性玻尔兹曼输运（LBT）模型模拟喷流在介质中的传播，该模型考虑了喷流与介质之间的弹性及非弹性相互作用。我们的理论计算结果显示，LBT模型计算得到的 Pb+Pb 在 $\sqrt{s}=5.02$ TeV 能区的 $\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$分布比 $p$+$p$的更窄，这与最近的ALICE测量结果非常吻合。 $\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$的收窄似乎违反了喷淋效应的$p_T$广义性质，通常用“选择偏差”的影响来解释这一现象。然而，物理细节仍需完全理解。 利用匹配喷淋方法追踪夸克胶子等离子体中的喷淋演化以消除蒙特卡洛模拟中的选择偏差，我们观察到由于喷淋-介质相互作用，$\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$分布变得更宽。 同时，通过将 Pb+Pb 碰撞中的夸克/胶子喷淋分数重新调整为与$p$+$p$相同，我们发现分数变化可能不会显著影响喷淋$\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$的修改模式。 另一方面，在A+A碰撞中选择的喷射样本具有比$p$+$p$基线显著更窄的初始$\Delta R_{{\rm axis}}^{{\rm WTA-Std}}$分布，并且这种在$p$+$p$和A+A之间的有偏比较掩盖了实验测量中实际的喷射展宽效应。 本文中的研究将深化我们对QGP中实际喷射修正与实验观测之间关系的理解。