Given the high luminosities at which CERN's Large Hadron Collider (LHC) operates, multiple proton-proton collisions occur during the same bunch crossing. Hard collisions are therefore contaminated by several soft, zero-bias, ones. This effect, known as pileup pollutes the reconstruction of the final state of the collision. This document is meant to provide a theoretical review of the methods employed during Run I of the LHC and at the beginning of Run II to mitigate pileup effects. I will start with a in-depth presentation of the area-median used for the vast majority of applications, including several refinements of the original idea, their practical (numerical) implementation and an assessment of their efficiency and robustness. I will then focus on several theoretical calculations that can provide both quantitative and qualitative information on the area-median approach. In the specific case of boosted jets, a field that has seen a wide interest recently, a set of methods, known as grooming techniques has also been used. I will describe these techniques, address their performance and briefly show that they are amenable to a theoretical, analytic, understanding. The last part of this review will focus on ideas oriented towards future pileup mitigation techniques. This includes a couple of new methods that have recently been proposed as well as a large series of alternative methods. The latter are yet unpublished and have not received the same amount of investigation than the former but they have the potential to bring new developments and further improvement over existing techniques in a future where pileup mitigation will be crucial.

中文翻译：

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LHC 理论家的观点中的堆积缓解

鉴于欧洲核子研究中心的大型强子对撞机 (LHC) 运行的高光度，在同一束交叉期间会发生多次质子-质子碰撞。因此，硬碰撞被几个软的、零偏差的碰撞所污染。这种称为堆积的效应会污染碰撞最终状态的重建。本文件旨在对 LHC 的运行 I 期间和运行 II 开始时采用的方法进行理论回顾，以减轻堆积效应。我将首先深入介绍用于绝大多数应用程序的面积中值，包括对原始想法的一些改进、它们的实际（数字）实现以及对它们的效率和稳健性的评估。然后，我将重点介绍几种理论计算，这些计算可以提供关于面积中值方法的定量和定性信息。在助推喷气机这个最近引起广泛兴趣的领域的特定情况下，还使用了一组称为修饰技术的方法。我将描述这些技术，解决它们的性能，并简要说明它们适用于理论、分析和理解。本次审查的最后一部分将侧重于面向未来堆积缓解技术的想法。这包括最近提出的几种新方法以及大量替代方法。