Theoretical Particle Physics Rolling Grant

理论粒子物理滚动资助

• 批准号: ST/G000484/1
• 负责人: Robert Thorne
• 金额: $ 24.4万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FG000484%2F1
• 关键词: Theoretical; Particle; Physics; Rolling; Grant

In order to reach the highest possible energies, the current particle colliders, the DESY electron-positron collider at Hamburg (which finished running in 2007, but from which data are continuing to appear) and the Tevatron proton-antiproton collider near Chicago, use protons as at least one of their colliding particles. Protons are particles which interact via the strong force, and are composite particles because the strong force binds the fundamental constituents, partons - which may be quarks or gluons. The collider due to turn on at CERN, the Large Hadron Collider (LHC), will be a proton-proton collider. The LHC will achieve the highest energies at a particle collider by a factor of more than 7, and will enable us to see if the missing particle within the Standard Model of particle physics, the Higgs boson, exists - as well as to detect the first signs of physics beyond the Standard Model, for example Supersymmetry, where each Standard Model particle has a supersymmetric partner. At low energies we think of the partons as being bound within the proton, but at very high energies the strong coupling becomes weaker, and the interactions of colliding protons can be thought of as interactions between the partons in each proton, which may be calculated as an expansion in the strong coupling constant. Hence, in order to understand the results of any hadron collider experiments one must first understand how the proton is made up out of its partonic constituents. To a certain degree this can be calculated, but the strong coupling makes some expansions badly defined, and some of the information must be determined by comparison with experimental data. Therefore, one must perform enough independent experiments, and use the theoretical calculations within the theory of the strong force (Quantum ChromoDynamics - QCD) as accurately as possible, to determine the composition of the proton in terms of the gluons and the six flavours of quark (up, down, strange, charm, bottom and top). This requires the use of data from a variety of experiments, and it must be checked that all pieces of data are consistent with the partons and the QCD theory, hence testing QCD to great accuracy, and measuring the strong coupling. Once a consistent set of parton distributions is determined, these partons may be used to predict any other process using the protons. This can be the production of beyond the Standard Model particles, or for Standard Model processes, where the latter often mask the former. The project proposed is to improve the determination of parton distributions and their consequences for collider physics. This will be achieved by incorporating new theoretical calculations, e.g. higher order in the coupling or more precise inclusion of heavy particle corrections, and also by the inclusion of data on new processes, both from the existing colliders and from the forthcoming LHC. These new theoretical developments and the new influx of data will mean we require a lot of effort to obtain the best partons. However, this is essential if the data are to be interpreted properly, and hence, if we are to increase our understanding of the Standard Model and also to search for the physics beyond it. It is very likely that any signal for new physics at the LHC will initially be ambiguous, since it could be due to an uncertainty in our understanding of the Standard Model, in particular strong interaction physics and parton distributions, and this has previously occurred at other hadron colliders. The group at UCL has the precise expertise to disentangle these possibilities due to both the experience in analysing numerous different types of data sets in comparison to predictions, and in developing improvements to the theoretical framework. In the case that a new signal is observed, the group will aim to help interpret precisely what it signifies, where again the ability to separate it out from the background will be vital.

为了达到尽可能高的能量，目前的粒子对撞机，汉堡的DESY正电子对撞机（2007年结束运行，但数据仍在继续出现）和芝加哥附近的Tevatron质子-反质子对撞机，至少使用质子作为它们的碰撞粒子之一。质子是一种通过强作用力相互作用的粒子，也是一种复合粒子，因为强作用力将基本成分——部分——结合在一起，部分可能是夸克或胶子。即将在欧洲核子研究中心启动的大型强子对撞机（LHC）将是一个质子-质子对撞机。大型强子对撞机将达到粒子对撞机中最高能量的7倍以上，并将使我们能够看到粒子物理标准模型中缺失的粒子希格斯玻色子是否存在，以及探测超出标准模型的物理的第一个迹象，例如超对称，每个标准模型粒子都有一个超对称的伙伴。在低能时，我们认为粒子被束缚在质子内，但在高能时，强耦合变得较弱，碰撞质子之间的相互作用可以被认为是每个质子中粒子之间的相互作用，这可以被计算为强耦合常数的膨胀。因此，为了理解强子对撞机实验的结果，我们必须首先理解质子是如何由它的部分子成分组成的。在一定程度上，这是可以计算的，但强耦合使得一些展开式定义不好，一些信息必须通过与实验数据的比较来确定。因此，必须进行足够的独立实验，并尽可能准确地使用强作用力理论（量子色动力学- QCD）中的理论计算，以确定质子的胶子和六种夸克（上、下、奇、粲、底和顶）的组成。这需要使用来自各种实验的数据，并且必须检查所有数据都与部分和QCD理论一致，从而以很高的精度测试QCD，并测量强耦合。一旦确定了一组一致的部分分布，这些部分就可以用来预测使用质子的任何其他过程。这可能是超出标准模型粒子的产物，也可能是标准模型过程的产物，后者往往掩盖了前者。提出的项目是为了改进对撞机物理中部分子分布及其结果的确定。这将通过结合新的理论计算来实现，例如更高阶的耦合或更精确地包含重粒子修正，以及包括来自现有对撞机和即将到来的大型强子对撞机的新过程的数据。这些新的理论发展和新的数据涌入意味着我们需要付出很大的努力来获得最佳的部分。然而，如果要正确地解释数据，因此，如果我们要增加对标准模型的理解，并寻找超越标准模型的物理学，这是必不可少的。在大型强子对撞机上，任何新物理学的信号最初都很可能是模糊的，因为这可能是由于我们对标准模型的理解存在不确定性，特别是强相互作用物理学和部分子分布，而这在其他强子对撞机上已经发生过。伦敦大学学院的研究小组拥有精确的专业知识来解开这些可能性，因为他们在分析众多不同类型的数据集与预测相比较方面的经验，以及在改进理论框架方面的经验。在观察到新信号的情况下，该小组将致力于帮助准确地解释它的含义，在这种情况下，将它从背景中分离出来的能力将至关重要。

项目成果

Heavy-quark mass dependence in global PDF analyses and 3- and 4-flavour parton distributions

• DOI: 10.1140/epjc/s10052-010-1462-8
• 发表时间: 2010-07
• 期刊: The European Physical Journal C
• 作者: A. Martin;W. Stirling;R. Thorne;G. Watt

PDF dependence of Higgs cross sections at the Tevatron and LHC: response to recent criticism

• DOI: 10.1007/jhep08(2011)100
• 发表时间: 2011-06
• 期刊: Journal of High Energy Physics
• 影响因子: 5.4
• 作者: R. Thorne;G. Watt

Lepton flavor violation in complex SUSY seesaw models with nearly tribimaximal mixing

• DOI: 10.1007/jhep01(2011)004
• 发表时间: 2010-11
• 期刊: Journal of High Energy Physics
• 影响因子: 5.4
• 作者: F. Deppisch;F. Plentinger;G. Seidl

Central exclusive production in QCD

QCD 中央独家生产

• DOI: 10.1007/jhep01(2010)121
• 发表时间: 2010
• 期刊: Journal of High Energy Physics
• 影响因子: 5.4
• 作者: Coughlin T

Central Exclusive Particle Production at High Energy Hadron Colliders

• DOI: 10.1016/j.ppnp.2010.06.001
• 发表时间: 2010-06
• 期刊: Progress in Particle and Nuclear Physics
• 影响因子: 9.6
• 作者: M. Albrow;T. Coughlin;J. Forshaw