Tuning of Monte Carlo Event Generators

蒙特卡罗事件生成器的调整

• 批准号: PP/E00699X/1
• 负责人: Peter Richardson
• 金额: $ 11.58万
• 依托单位: Durham University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=PP%2FE00699X%2F1
• 关键词: Tuning; Monte; Carlo; Event; Generators

Physics at the Large Hadron Collider (LHC) is likely to involve a bewildering array of new phenomena, due to new heavy particles which have never been produced before with a man-made particle collider. At present, we have no idea what the characteristics of these particles will be, but there are many theoretical models which predict particular arrangements. These include such exciting ideas as 'supersymmetry', which at least requires a doubling of the number of known fundamental particles; the existence of extra dimensions, which would be a deeply profound discovery; or a menagerie of other variations. Any of these, if discovered, would be a giant leap forward in our understanding of the universe. Much of LHC physics will be geared towards working out which, if any, of these models is realised in nature. Part of the reason that LHC physics will be difficult is that the phenomena that particle physics has spent the past 50 years investigating to such high accuracy - the extraordinarily successful 'Standard Model' (SM) - will be a huge source of 'background noise' in measurements of new physics. To study the new, heavy particles, we must first have excellent control of the SM physics which threatens to hide them. If our models of the SM are not accurate, it may be impossible to extract clean signals of the new particles. Or, perhaps worse, we could accidentally claim the discovery of something which is not actually there! Understanding how the SM manifests itself in collider experiments is not easy: in particular, the strong nuclear force is problematic when it comes to making calculations. This force 'glues together' fundamental 'quark' particles, which are never seen in isolation, to make the observed 'hadron' particles like protons and neutrons. Calculations made using QED, the SM theory of electromagnetism, rapidly converge to accurate predictions, but the corresponding calculations in QCD, the strong force theory, are extremely complex and the convergence rate is much slower. There are also aspects of QCD which cannot be handled by normal methods: for example, the process by which quarks bind strongly into hadrons is not well understood. To get around these calculational problems, particle physicists use computer simulations which, rather than calculating everything from the most fundamental QCD ideas upwards, take a more approximate path. These simulations, called 'event generators', simulate all aspects of particle collisions, from the most energetic interactions, to the spray of particles that come from a high energy quark, and to the eventual low-energy conversions of quarks into hadrons. The price that one must pay for such a calculational shortcut is predictivity: where a genuine QCD calculation, albeit one massively beyond any known methods, would only require a few numbers to be specified, event generators have a lot of input parameters. The only real test of whether or not the values given are 'good' is how well the event generator predictions compare to real measurements. This is of enormous importance to LHC physics: unless the QCD backgrounds to new physics are understood, in the form of reliable event generator tunings, all the new and exciting physics may remain hidden. With so many parameters, however, working out which combinations are good is a substantial task in itself. The aim of this project is to systematically tune all the major event generators to be used at the LHC against all the available data, so that QCD backgrounds to new physics are well-modelled. It is important that the data against which the generators are tuned includes that from the LHC itself, as areas of QCD which have never been probed before will be encountered there. With a good control of QCD models, the new physics which the LHC was built to find can be reliably identified and studied, perhaps changing our view of the universe forever.

大型强子对撞机（LHC）的物理学很可能涉及一系列令人困惑的新现象，这是由于以前从未用人造粒子对撞机产生过的新的重粒子。目前，我们还不知道这些粒子的特性是什么，但有许多理论模型可以预测特定的排列。其中包括令人兴奋的想法，如“超自然”，这至少需要将已知的基本粒子数量增加一倍;额外维度的存在，这将是一个非常深刻的发现;或者其他变体的动物园。如果发现了其中的任何一个，都将是我们对宇宙理解的一个巨大飞跃。LHC的大部分物理学将致力于研究这些模型中的哪一个（如果有的话）在自然界中得以实现。LHC物理学困难的部分原因是，粒子物理学在过去50年里以如此高的精度研究的现象-非常成功的“标准模型”（SM）-将成为测量新物理学的“背景噪音”的巨大来源。为了研究新的重粒子，我们必须首先对有可能隐藏它们的SM物理学有很好的控制。如果我们的SM模型不准确，就不可能提取新粒子的干净信号。或者，也许更糟的是，我们可能会意外地声称发现了一些实际上并不存在的东西！理解SM如何在对撞机实验中表现出来并不容易：特别是在计算时，强核力是有问题的。这种力将基本的“夸克”粒子“粘合在一起”，这些粒子从未单独出现过，使观察到的“强子”粒子像质子和中子一样。使用QED（电磁学的SM理论）进行的计算可以快速收敛到精确的预测，但QCD（强作用力理论）中的相应计算非常复杂，收敛速度要慢得多。QCD也有一些方面不能用常规方法处理：例如，夸克与强子强烈结合的过程还没有得到很好的理解。为了解决这些计算问题，粒子物理学家使用计算机模拟，而不是从最基本的QCD思想开始计算所有内容，而是采取更近似的方法。这些模拟称为“事件发生器”，模拟粒子碰撞的所有方面，从最具能量的相互作用，到来自高能夸克的粒子喷雾，以及夸克到强子的最终低能转换。为这种计算捷径必须付出的代价是预测性：真正的QCD计算，尽管远远超出任何已知的方法，只需要指定几个数字，事件生成器有很多输入参数。对给定值是否“好”的唯一真实的测试是将事件生成器的预测与真实的测量进行比较。这对LHC物理学来说非常重要：除非以可靠的事件发生器调谐的形式理解新物理学的QCD背景，否则所有新的和令人兴奋的物理学可能仍然被隐藏。然而，有这么多的参数，找出哪些组合是好的本身就是一项艰巨的任务。这个项目的目的是系统地调整所有的主要事件发生器将在大型强子对撞机对所有可用的数据，使QCD背景的新物理是很好的模型。重要的是，调整发生器的数据包括来自LHC本身的数据，因为在那里将遇到以前从未探测过的QCD区域。有了对QCD模型的良好控制，LHC所要寻找的新物理可以被可靠地识别和研究，也许会永远改变我们对宇宙的看法。

项目成果

Rivet user manual

• DOI: 10.1016/j.cpc.2013.05.021
• 发表时间: 2013-12-01
• 期刊: COMPUTER PHYSICS COMMUNICATIONS
• 影响因子: 6.3
• 作者: Buckley, Andy;Butterworth, Jonathan;Siegert, Frank
• 通讯作者: Siegert, Frank

Monte Carlo tuning and generator validation

蒙特卡罗调整和生成器验证

• 作者: Buckley Andy

Developments in MC event generator tuning and systematics

MC 事件生成器调优和系统学的发展

• DOI: 10.1109/nssmic.2010.5873737
• 发表时间: 2010
• 作者: Buckley A

Tools for event generator tuning and validation

用于事件生成器调整和验证的工具

• DOI: 10.3204/desy-proc-2009-02/49
• 作者: Buckley Andy

New developments in event generator tuning techniques

事件生成器调优技术的新进展

• DOI: 10.22323/1.093.0079
• 发表时间: 2011
• 作者: Schulz H