In this paper, we investigate the medium modifications of girth distributions for inclusive jets and tagged jets with a small radius ( ) in Pb+Pb collisions with TeV at the LHC. The partonic spectra in the initial hard scattering of elementary collisions are obtained by an event generator POWHEG+PYTHIA, which matches the next-to-leading order (NLO) matrix elements with parton showering, and the energy loss of a fast parton traversing the hot/dense QCD medium is calculated by Monte Carlo simulation within the higher-twist formalism of jet quenching in heavy-ion collisions. We present the model calculations of event normalized girth distributions for inclusive jets in p+p and Pb+Pb collisions at TeV, which give good descriptions of ALICE measurements. It is shown that the girth distributions of inclusive jets in Pb+Pb are shifted to lower girth regions relative to those in p+p. Thus, the nuclear modification factor of girth distributions for inclusive jets is larger than unity at small girth regions and smaller than unity at large girth regions. This behavior results from softer fragments inside a jet as well as the fraction alteration of gluon/quark initiated jets in heavy-ion collisions. We further predict the girth distributions for boson tagged jets in Pb+Pb collisions at TeV and demonstrate that the medium modification on girth distributions for tagged jets is less pronounced compared to that for inclusive jets because the dominant components of tagged jets are quark-initiated jets.

在本文中，我们研究了 LHC上 Pb+Pb 与TeV碰撞中包含射流和小半径 ( ) 标记射流的周长分布的中等修正。通过事件发生器 POWHEG+PYTHIA 获得基本碰撞初始硬散射中的分子光谱，该事件发生器将次领先阶 (NLO) 矩阵元素与部分子阵雨和快速部分子穿过热的能量损失相匹配/dense QCD 介质是通过蒙特卡罗模拟在重离子碰撞中射流淬火的高扭曲形式中计算的。我们提出了p + p和 Pb + Pb 碰撞中包容性射流的事件归一化周长分布的模型计算TeV，它很好地描述了 ALICE 测量值。结果表明，相对于p + p中的那些，Pb+Pb 中包容射流的周长分布向较低的周长区域移动。因此，包容射流的周长分布的核修正因子在小周长区域大于一，在大周长区域小于一。这种行为是由于射流内部较软的碎片以及重离子碰撞中胶子/夸克引发的射流的分数变化造成的。我们进一步预测了在 TeV 的 Pb+Pb 碰撞中玻色子标记喷流的周长分布，并证明了对周长分布的介质修改与包容性喷流相比，带标记的喷流不太明显，因为带标记的喷流的主要成分是夸克引发的喷流。