Jet measurements in heavy ion physics
Jet measurements in heavy ion physics
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DOI：
10.1103/revmodphys.90.025005
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发表时间：
2017-05
影响因子：
44.1
通讯作者：
M. Connors;C. Nattrass;R. Reed;S. Salur
中科院分区：
文献类型：
--
作者：
M. Connors;C. Nattrass;R. Reed;S. Salur
在超相对论重离子碰撞中产生了一种称为夸克胶子等离子体（QGP）的热的稠密介质。在碰撞的早期，硬部分子散射产生高动量的部分子，穿过介质，然后分裂成称为喷流的粒子喷雾。了解这些部分子如何与QGP相互作用并碎裂成末态粒子，为量子色动力学提供了重要的见解。相对论重离子对撞机（RHIC）和大型强子对撞机（LHC）的高动量强子、两粒子关联和全喷流重建的实验测量继续提高我们对QGP能量损失的理解。LHC的运行2最近开始，RHIC正在开发一个喷流探测器。现在是一个完美的时间来思考到目前为止实验测量所教给我们的东西，用于研究喷流的技术的局限性，如何改进这些技术，以及如何利用丰富的实验数据来实现对QGP中能量损失的完整描述。迄今为止对喷流的测量清楚地表明，硬部分子会损失能量。详细的核修饰因子之间的数据和模型计算的比较导致定量限制的不透明度的介质硬探头。然而，虽然有大量的证据软化和扩大射流通过介质的相互作用，比较测量理论计算的困难限制了进一步的定量约束的能量损失机制。由于喷流是初始部分子的算法描述，因此在进行数据和理论比较时，必须使用相同的喷流定义，包括对基础重离子背景的处理。理论家和实验学家之间需要就背景的适当处理达成一致，蒙特卡罗生成器使实验算法能够应用于理论计算，并清楚地了解哪些可观测量对介质的性质最敏感，即使在存在背景的情况下。这将使我们能够确定该领域的最佳策略，以在面对这些挑战时改善对介质特性的定量约束。
A hot, dense medium called a quark gluon plasma (QGP) is created in ultrarelativistic heavy ion collisions. Early in the collision, hard parton scatterings generate high momentum partons that traverse the medium, which then fragment into sprays of particles called jets. Understanding how these partons interact with the QGP and fragment into final state particles provides critical insight into quantum chromodynamics. Experimental measurements from high momentum hadrons, two particle correlations, and full jet reconstruction at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) continue to improve our understanding of energy loss in the QGP. Run 2 at the LHC recently began and there is a jet detector at RHIC under development. Now is the perfect time to reflect on what the experimental measurements have taught us so far, the limitations of the techniques used for studying jets, how the techniques can be improved, and how to move forward with the wealth of experimental data such that a complete description of energy loss in the QGP can be achieved. Measurements of jets to date clearly indicate that hard partons lose energy. Detailed comparisons of the nuclear modification factor between data and model calculations led to quantitative constraints on the opacity of the medium to hard probes. However, while there is substantial evidence for softening and broadening jets through medium interactions, the difficulties comparing measurements to theoretical calculations limit further quantitative constraints on energy loss mechanisms. Since jets are algorithmic descriptions of the initial parton, the same jet definitions must be used, including the treatment of the underlying heavy ion background, when making data and theory comparisons. An agreement is called for between theorists and experimentalists on the appropriate treatment of the background, Monte Carlo generators that enable experimental algorithms to be applied to theoretical calculations, and a clear understanding of which observables are most sensitive to the properties of the medium, even in the presence of background. This will enable us to determine the best strategy for the field to improve quantitative constraints on properties of the medium in the face of these challenges.