利用ATLAS探测器测量5.02 TeV铅核-铅核对撞中b-喷注的核修正因子
Measurement of the nuclear modification factor of $b$-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector
AI总结：
本研究利用ATLAS探测器测量5.02 TeV铅核-铅核与质子-质子对撞中的b-喷注及遍举喷注核修正因子，发现b-喷注核修正因子从边缘到中心对撞下降，且中心对撞中高于遍举喷注，为部分子能量损失的质量与色荷效应提供实验依据。
摘要：
本文介绍了在大型强子对撞机（LHC）上利用ATLAS探测器，在质心系核子-核子能量$\boldsymbol{\bar{s}_{_{NN}}=5.02}$ TeV下开展的铅核-铅核（Pb+Pb）与质子-质子（$pp$）对撞中b-喷注产生的测量工作。本次测量使用了2017年采集的积分亮度为260 $\textrm{pb}^{-1}$的$pp$对撞数据，以及2018年采集的积分亮度为1.4 $\textrm{nb}^{-1}$的Pb+Pb对撞数据。在两种对撞系统中，喷注均通过anti-$k_{t}$算法重建。b-喷注的识别以含b-夸克半轻衰变产生的μ子的喷注样本为基础，采用μ子相对于喷注轴的动量模板拟合方法实现。在$pp$对撞中，重建了半径参数$R=0.2$和$R=0.4$的b-喷注；而在Pb+Pb对撞中仅使用$R=0.2$的喷注。作为对比，研究还利用2018年采集的积分亮度为1.7 $\textrm{nb}^{-1}$的Pb+Pb对撞数据，以及与b-喷注测量相同的$pp$对撞数据，测量了$R=0.2$的遍举喷注。研究计算了横动量范围80--290 GeV内，$R=0.2$的b-喷注与遍举喷注的核修正因子$R_\ extrm{AA}$。b-喷注的核修正因子从边缘对撞到中心对撞呈下降趋势。研究还给出了b-喷注$R_\ extrm{AA}$与遍举喷注$R_\ extrm{AA}$的比值，结果表明在中心Pb+Pb对撞中，b-喷注的$R_\ extrm{AA}$大于遍举喷注的$R_\ extrm{AA}$。这些测量结果与理论计算的对比显示，质量效应与色荷效应在重离子对撞的部分子能量损失中发挥作用。
英文摘要：
This paper presents a measurement of $b$-jet production in Pb+Pb and $pp$ collisions at $\sqrt{s_{_\textrm{NN}}}=5.02$ TeV with the ATLAS detector at the LHC. The measurement uses 260 $\textrm{pb}^{-1}$ of $pp$ collisions collected in 2017 and 1.4 $\textrm{nb}^{-1}$ of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti-$k_{t}$ algorithm. The $b$-jets are identified from a sample of jets containing muons from the semileptonic decay of $b$-quarks using template fits of the muon momentum relative to the jet axis. In $pp$ collisions, $b$-jets are reconstructed for radius parameters $R= 0.2$ and $R= 0.4$, and only $R= 0.2$ jets are used in Pb+Pb collisions. For comparison, inclusive $R= 0.2$ jets are also measured using 1.7 $\textrm{nb}^{-1}$ of Pb+Pb collisions collected in 2018 and the same $pp$ collision data as the $b$-jet measurement. The nuclear modification factor, $R_\textrm{AA}$, is calculated for both $b$-jets and inclusive jets with $R= 0.2$ over the transverse momentum range of 80--290 GeV. The nuclear modification factor for $b$-jets decreases from peripheral to central collisions. The ratio of the $b$-jet $R_\textrm{AA}$ to inclusive jet $R_\textrm{AA}$ is also presented and suggests that the $R_\textrm{AA}$ for $b$-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.
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