"Figure 7-3" of "First measurement of large area jet transverse momentum spectra in heavy-ion collisions"

Jet production in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is studied with the CMS detector at the LHC, using PbPb and pp data samples corresponding to integrated luminosities of 404/μb and 27.4/pb, respectively. Jets with different areas are reconstructed using the anti-kT algorithm by varying the distance parameter R. The measurements are performed using jets with transverse momenta (pT) greater than 200 GeV and in a pseudorapidity range of |eta|< 2. To reveal the medium modification of the jet spectra in PbPb collisions, the properly normalized ratio of spectra from PbPb and pp data is used to extract jet nuclear modification factors as functions of the PbPb collision centrality, pT and, for the first time, as a function of R up to 1.0. For the most central collisions, a strong suppression is observed for high-pT jets reconstructed with all distance parameters, implying that a significant amount of jet energy is scattered to large angles. The dependence of jet suppression on R is expected to be sensitive to both the jet energy loss mechanism and the medium response, and so the data are compared to several modern event generators and analytic calculations. The models considered do not fully reproduce the data.本研究依托大型强子对撞机（Large Hadron Collider, LHC）上的紧凑型缪子线圈（Compact Muon Solenoid, CMS）探测器，针对核子-核子质心系能量为5.02 TeV的铅-铅（PbPb）与质子-质子（pp）碰撞中的喷注产生过程开展分析，所用PbPb和pp数据样本的积分亮度分别为404/μb与27.4/pb。研究通过调整距离参数R，采用反kT（anti-kT）算法重建不同面积的喷注，测量对象为横向动量（transverse momenta, pT）大于200 GeV、赝快度满足|η|<2的喷注。为揭示PbPb碰撞中喷注能谱的介质修正效应，本研究通过对PbPb与pp数据的能谱比值进行恰当归一化，提取喷注核修正因子（jet nuclear modification factors），该修正因子可分别作为PbPb碰撞中心度、pT的函数，同时首次以R（最大值至1.0）为自变量进行分析。对于最中心的碰撞事件，所有距离参数下重建的高pT喷注均呈现显著的抑制现象，这表明大量喷注能量被散射至大角度区间。喷注抑制效应对R的依赖关系对喷注能量损失机制与介质响应均具有敏感依赖性，因此本研究将实验数据与多款现代事件产生器（event generators）及解析计算结果进行对比，结果显示所考量的模型无法完全复现实验观测数据。