标题： 揭示高能核碰撞中$γ-$粒子束的角扩展 显示英文标题

标题： Unveiling the jet angular broadening with $γ-$jet in high-energy nuclear collisions

摘要： 中等的喷注结构在热密核物质中的修改近年来引起了重离子物理界的极大兴趣。 包括喷注的测量显示在核-核碰撞中角度变窄，而最近CMS对光子标记喷注（$\gamma-$喷注）的结果表明有扩宽的迹象。 在本工作中，我们采用考虑喷注能量损失和夸克胶子等离子体中介质响应的输运方法，对包括喷注和$\gamma-$喷注的角度结构进行了理论研究。 我们在$\gamma-$喷注的$0-30\%$PbPb碰撞中进行了宽度修改，在$\sqrt{s_{NN}}=$5.02 TeV下，结果与最近的CMS测量有良好的一致性。 我们探讨了在选择不同$x_{j\gamma}=p_T^{\rm jet}/p_T^{\gamma}$阈值时选择偏差与喷注动量之间的联系。 重要的是，我们定量地证明了$\gamma-$喷注能显著减少选择偏差，并且相比包括喷注能更有效地收集在PbPb碰撞中充分淬灭的喷注，这对于捕捉CMS观察到的喷注角度扩宽至关重要。 我们进一步估计了介质诱导的胶子辐射和介质响应对喷注角度子结构扩宽的贡献。 显示英文摘要

摘要： Medium modification of jet substructure within the hot and dense nuclear matter has attracted enormous interest from the heavy-ion physics community in recent years. Measurements of inclusive jet show the angular narrowing in nucleus-nucleus collisions, while the recent CMS results of the photon-tagged jets ($\gamma-$jet) indicate hints of broadening. In this work, we conduct a theoretical study on the angular structure of inclusive jet and $\gamma-$jet with a transport approach considering the jet energy loss and the medium response in the quark-gluon plasma. We carry out the girth modification of $\gamma-$jet in $0-30\%$ PbPb collisions at $\sqrt{s_{NN}}=$ 5.02 TeV, which shows a satisfactory agreement with the recent CMS measurement. We explore the connection between the selection bias and the jet kinematics when choosing different $x_{j\gamma}=p_T^{\rm jet}/p_T^{\gamma}$ threshold. Importantly, we quantitatively demonstrate that $\gamma-$jet provides significant advantages to reduce the selection bias and can effectively collect jets sufficiently quenched in PbPb collisions compared to the inclusive jet, which is critical to capture the jet angular broadening observed by CMS. We further estimate the contributions of the medium-induced gluon radiation and the medium response to the broadening of the jet angular substructure.