用ATLAS探测器测量在$\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV上Pb+Pb和$pp$碰撞中喷流内和周围带电粒子的角和动量分布
Measurement of angular and momentum distributions of charged particles within and around jets in Pb+Pb and $pp$ collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV with the ATLAS detector
摘要：
对重离子碰撞中喷流碎裂成带电粒子的研究，可以提供关于这种碰撞中产生的热而致密的QCD物质（夸克-胶子等离子体）对喷流淬灭机制的信息。本文介绍了在大型强子对撞机（LHC）上用ATLAS探测器测量了$\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV Pb+Pb和$pp$碰撞中带电粒子绕喷流轴的角分布。Pb+Pb和$pp$数据集的积分光度分别为0.49 nb $^{-1}$和25 pb $^{-1}$。测量是针对用具有半径参数$R = 0.4$的反$k_{t}$算法重建的射流执行的，并且延伸到距射流轴线的角距离$r= 0.8$。结果作为一个函数的Pb+Pb碰撞中心和距离射流轴的带电粒子的横向动量在1 $-$ 63 GeV的范围内，匹配的横向动量在126 $-$ 316 GeV的范围和喷射速度的绝对值小于1.7的射流。通过对$pp$碰撞中的测量值取一个比率来量化对测量分布的修改。产率的带电粒子与横向动量低于4 GeV的观察到越来越多的增强作为一个函数的角距离从射流轴，达到最大值在$r=0.6$。带电粒子的横向动量超过4 GeV的有一个增强的收益率在Pb+Pb碰撞的喷流核心的角距离高达$r = 0.05$从喷流轴，在更大的距离抑制。
英文摘要：
Studies of the fragmentation of jets into charged particles in heavy-ion collisions can provide information about the mechanism of jet-quenching by the hot and dense QCD matter created in such collisions, the quark-gluon plasma. This paper presents a measurement of the angular distribution of charged particles around the jet axis in $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV Pb+Pb and $pp$ collisions, using the ATLAS detector at the LHC. The Pb+Pb and $pp$ data sets have integrated luminosities of 0.49 nb$^{-1}$ and 25 pb$^{-1}$, respectively. The measurement is performed for jets reconstructed with the anti-$k_{t}$ algorithm with radius parameter $R = 0.4$ and is extended to an angular distance of $r= 0.8$ from the jet axis. Results are presented as a function of Pb+Pb collision centrality and distance from the jet axis for charged particles with transverse momenta in the 1$-$63 GeV range, matched to jets with transverse momenta in the 126$-$316 GeV range and an absolute value of jet rapidity of less than 1.7. Modifications to the measured distributions are quantified by taking a ratio to the measurements in $pp$ collisions. Yields of charged particles with transverse momenta below 4 GeV are observed to be increasingly enhanced as a function of angular distance from the jet axis, reaching a maximum at $r=0.6$. Charged particles with transverse momenta above 4 GeV have an enhanced yield in Pb+Pb collisions in the jet core for angular distances up to $r = 0.05$ from the jet axis, with a suppression at larger distances.
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