Top Quark Physics and Search for Higgs Bosons at Hadron Colliders

强子对撞机上的顶级夸克物理和希格斯玻色子搜索

• 批准号: PP/E006094/1
• 负责人: Christian Schwanenberger
• 金额: $ 57.73万
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=PP%2FE006094%2F1
• 关键词: Top; Quark; Physics; Search; Higgs

We particle physicists are trying to answer a very old question - posed e.g. by Goethe's Faust almost 200 years ago: 'So that I may perceive whatever holds the world together in its inmost folds'. In our current understanding matter consists of molecules, which are formed by atoms, which in turn consist of a cloud of electrons orbiting a nucleus. The latter is made of protons and neutrons. While there is no hint of a substructure of electrons, protons and neutrons are made of two types of quarks. No substructure has yet been found for quarks. So we call electrons and quarks elementary particles. However, today we know a lot more elementary particles, e.g. six different types of quarks. How could we find all that out? The principle is rather easy: we shoot particles onto each other and analyse the debris. This tells us what kind of particles exist and what kind of forces govern their interaction. The faster the initial particles are, the deeper we can look into matter and the heavier particles we can find. So we build larger and larger colliders to accelerate the initial particles to higher and higher energies to get a better and better knowledge about the structure of matter. Then we must build huge detectors to reconstruct the debris particles. For instance, their direction can be 'seen' due to the fact that they leave a track in the detector like a plane leaves a condensation trail in the sky. This helps us to identify them. The Large Hadron Collider (LHC) currently under construction at CERN, near Geneva, will be the highest energy collider ever built. In a ring 27 km around it will accelerate two beams of protons to nearly the speed of light before they will be collided head-on. Several detectors will record these collisions. However, many more collisions will happen than can be recorded, up to one billion per second. In fact only 0.0005% of all beam crossings can be kept. A sophisticated system of purpose-built electronics and software algorithms decides which collision events are interesting and should thus be saved. I intend to work on one of the LHC detectors, called ATLAS and help construct this system and ensure its efficient operation. What questions do I hope to answer with the data thus collected? First of all, I am interested in the heaviest known elementary particle, called the top quark. It was discovered only ten years ago at the Tevatron collider at Fermilab near Chicago. Now, of course, one wants to measure it in detail and e.g. find out if it behaves similarly to its five colleagues. At present I am measuring its properties, e.g. its mass, using the D0 detector at the Tevatron. I will continue this work and extend it to measurements at the LHC, where millions of top quarks will be produced. One main question about the top quark is: why is it so heavy, around 40 times heavier than any of the other quarks? And how do elementary particles acquire their mass at all? It is postulated that this happens by interaction with a new field, named after its inventor as the Higgs field. This theory also postulates the existence of a heavy particle, the Higgs particle. I intend to search for it at the LHC. At the LHC one will also search for many other 'new' particles. I am especially interested in particles which have a certain symmetry relation to the Higgs particle - one could even say, I will search for relatives of the Higgs particle. The possible discovery of these and other new particles will extend not only our knowledge of the sub-atomic world, but will even help our understanding of the composition of the whole universe. Astronomical observations show that there must be a much larger amount of matter present in the universe than can be seen - so-called dark matter. The composition of this dark matter, however, remains a mystery. If indeed new particles are discovered at the LHC, they could be candidates for this dark matter.

我们的粒子物理学家试图回答一个非常古老的问题 - 例如大约200年前，歌德的浮士德（Faust）：“这样我就可以感知到将世界充满最大折叠的一切。在我们目前的理解中，物质由分子组成，这些分子由原子形成，而原子又由绕核的电子云组成。后者由质子和中子制成。虽然没有迹象表明电子的子结构，但质子和中子是由两种类型的夸克制成的。 Quarks尚未找到子结构。因此，我们将电子和夸克基本粒子称为。但是，今天我们知道更多的基本粒子，例如六种不同类型的夸克。我们怎么能找到所有这些？原理很容易：我们相互射击颗粒并分析碎屑。这告诉我们存在什么样的粒子以及哪种力量控制它们的相互作用。初始颗粒的速度越快，我们可以发现物质越深，我们可以找到的较重的颗粒。因此，我们建造越来越大的山脉，以将初始粒子加速到越来越高的能量，以获得越来越多的对物质结构的了解。然后，我们必须构建巨大的探测器来重建碎屑颗粒。例如，由于它们像飞机一样在探测器中留下轨道，因此可以“看到”它们的方向。这有助于我们识别它们。当前在日内瓦附近Cern正在建设的大型强子撞机（LHC）将是有史以来最高的能源对撞机。在27公里的环中，它将在将它们碰撞之前将两束质子加速至几乎是光速。几个探测器会记录这些碰撞。但是，每秒最多可记录的碰撞将比记录多10亿。实际上，只能保留所有光束交叉口的0.0005％。专门构建的电子和软件算法的复杂系统决定了哪些碰撞事件很有趣，因此应保存。我打算在其中一个LHC检测器上工作，称为Atlas，并帮助构建该系统并确保其有效的操作。我希望从这样收集的数据回答什么问题？首先，我对最重的已知基本粒子感兴趣，称为顶级夸克。它是十年前在芝加哥附近费米拉布的Tevatron撞机机上发现的。现在，当然，一个人希望详细测量它，例如找出它的行为是否与五个同事相似。目前，我正在测量其特性，例如它的质量，使用Tevatron上的D0检测器。我将继续这项工作，并将其扩展到LHC的测量值，在那里将生产数百万个顶级夸克。关于顶级夸克的一个主要问题是：为什么它如此重，比其他任何夸克重40倍？基本颗粒如何完全获得质量？据推测，这是通过与新领域的互动来发生的，该领域以其发明者命名为Higgs字段。该理论还假设了一个重粒子的存在，即希格斯粒子。我打算在LHC搜索它。在LHC上，也将搜索许多其他“新”粒子。我对与希格斯粒子有一定对称性的粒子特别感兴趣 - 甚至可以说，我会搜索希格斯粒子的亲戚。这些和其他新粒子的可能发现不仅会扩展我们对亚原子世界的了解，而且还将帮助我们理解整个宇宙的组成。天文观察表明，宇宙中必须比所见的暗物质要大得多。然而，这种暗物质的组成仍然是一个谜。如果确实在LHC发现了新粒子，则可能是这种暗物质的候选者。