Theoretical Particle Physics Rolling Grant

为了达到尽可能高的能量，目前的粒子对撞机，在汉堡的DESY电子-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，使用质子作为至少一个碰撞粒子。质子是通过强力相互作用的粒子，并且是复合粒子，因为强力束缚基本成分，部分子-可能是夸克或胶子。欧洲核子研究中心即将启动的大型强子对撞机（LHC）将是一台质子-质子对撞机。大型强子对撞机将在粒子对撞机上获得超过7倍的最高能量，并将使我们能够看到粒子物理学标准模型中缺失的粒子希格斯玻色子是否存在-以及检测标准模型之外的物理学的第一个迹象，例如超对称性，其中每个标准模型粒子都有一个超对称伙伴。在低能量时，我们认为部分子被束缚在质子内，但在非常高的能量时，强耦合变得较弱，碰撞质子的相互作用可以被认为是每个质子中部分子之间的相互作用，这可以计算为强耦合常数的扩展。因此，为了理解任何强子对撞机实验的结果，我们必须首先理解质子是如何由其部分子成分组成的。在某种程度上，这是可以计算的，但强耦合使得一些展开式定义不好，并且一些信息必须通过与实验数据比较来确定。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（量子色动学- QCD）中的理论计算，以确定质子的胶子和夸克的六种味道（上，下，奇怪，魅力，底部和顶部）的组成。这需要使用来自各种实验的数据，并且必须检查所有的数据是否与部分子和QCD理论一致，从而非常准确地测试QCD，并测量强耦合。一旦确定了一组一致的部分子分布，这些部分子就可以用来预测任何其他使用质子的过程。这可能是超越标准模型的粒子的产生，或者是标准模型过程，后者经常掩盖前者。提出的项目是为了改善部分子分布的测定及其对对撞机物理的影响。这将通过纳入新的理论计算来实现，例如耦合中的高阶或更精确地包含重粒子修正，以及通过包含来自现有对撞机和即将到来的LHC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多努力才能获得最好的部分子。然而，如果要正确解释数据，这是必不可少的，因此，如果我们要增加我们对标准模型的理解，也要寻找超越它的物理。很可能，LHC的任何新物理的信号最初都是模糊的，因为它可能是由于我们对标准模型的理解的不确定性，特别是强相互作用物理和部分子分布，这在其他强子对撞机上也发生过。UCL的团队拥有精确的专业知识来解决这些可能性，因为他们在分析与预测相比的许多不同类型的数据集以及改进理论框架方面都有经验。在观察到新信号的情况下，该小组将致力于帮助准确解释它的含义，将其从背景中分离出来的能力也至关重要。

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.