Experimental Particle Physics Consolidated Grant 2019

基础物理学致力于回答以下重大问题：我们的宇宙是由什么构成的；它是如何演化的；是什么力量支配着它；它们如何塑造我们观察到的现象？在粒子物理学中，我们建立实验来研究宇宙中最小的组成部分，基本粒子，这样我们就可以用我们的发现来解决这些问题。我们关于基本粒子如何行为的知识被封装在一个称为标准模型的理论中。它具有巨大的预测能力，并为理解宇宙的本质提供了一个简单的框架，然而，我们也知道该理论是不完整的。通过最高能量的实验，我们测试预测，以确定我们理解的限度和我们理论的有效性。通过专门的精确度实验，我们能够以令人难以置信的精确度进行预测。理论和数据之间任何不一致的最微弱的痕迹都可能表明发现了新类型的物理学，并在理解宇宙本质方面向前迈进了一步。我们面临的最紧迫的问题之一是，为什么物质应该在宇宙中占据如此大的主导地位，而非反物质。物质和反物质在早期宇宙中应该是等量产生的，但现在很少自然地产生反物质。导致这一现象的物质和反物质之间的行为差异是一个谜，也是我们宇宙的一个决定性特征。没有这种差异，星系和行星就不可能形成，生命也就不可能存在。我们认为，中微子可能掌握着理解为什么会发生这种情况的关键。中微子是近一个世纪前发现的，是最易消逝的粒子。它们没有电荷，几乎不与物质相互作用，长期以来被认为根本没有质量(就像光子一样)。为了探测它们，我们不得不建造巨大但非常灵敏的探测器。我们的实验表明，中微子的质量非常小；正是这一点可能导致物质比反物质占优势。我们研究的一个重要部分是对中微子进行详细的测量，了解它们的质量，以及它们是否对我们这个物质主导的宇宙负责。希格斯粒子的发现标志着我们认识的新纪元。它证实了一种根本性的新实体的存在，这种实体遍及整个自然界，并将质量赋予基本粒子。如果没有希格斯粒子，电子就不可能与质子结合形成氢原子，而如果没有原子，我们的宇宙将是一个非常不同、没有生命的地方。在我们的实验中，我们研究希格斯来测量和理解它的行为。我们的动机是一种迷人的可能性，即希格斯粒子可能会帮助我们理解宇宙的黑暗面；神秘的暗物质。人们早就知道，星系中没有足够多的恒星可见，无法解释恒星围绕它们旋转的速度。我们最好的解释是，星系还含有质量大的、不可见的(暗)物质，这些物质提供了维持恒星在其轨道上运行所需的额外引力。计算表明，这种暗物质形成的宇宙面积是我们所看到的物质的五倍。希格斯粒子可以与暗物质相互作用，为我们提供了一种首次照亮宇宙黑暗部分的方法。天体物理观测还表明，宇宙的膨胀正在加速，就好像太空本身产生了压力一样。目前还不清楚这是如何发生的，尽管已经有人提出，渗透到宇宙中的未知(暗)能量可能会导致加速。暗能量和暗物质一起构成了宇宙的95%。换句话说，在我们现有的实验中，我们只研究和理解了5%的宇宙。我们必须更多地了解，我们已经加入了新的实验来研究暗能量，发现新的物理，并最终揭示宇宙的本质。

Fundamental physics strives to answer the big questions: what is our Universe made of; how did it evolve; what forces govern it and how do they shape the phenomena we observe? In particle physics we build experiments to examine the smallest constituents of the universe, fundamental particles, so that we can address these questions with our findings.Our knowledge of how fundamental particles behave is encapsulated in a theory called the Standard Model. It has enormous predictive power and provides a simple framework to understand the nature of the universe, however, we also know the theory is incomplete. With experiments at the highest energies, we test predictions to determine the limits of our understanding and the validity of our theory. With dedicated precision experiments we probe predictions at incredible levels of accuracy. The faintest trace of any disagreement between theory and data could indicate a discovery of new types of physics, and a step forward in understanding the nature of the Universe.One of the most pressing questions we have concerns why matter should dominate so much over anti-matter in the Universe. Matter and anti-matter should have been created in equal quantities in the early Universe, but very little anti-matter occurs naturally now. The difference in behaviour between matter and anti-matter that caused this is a mystery, and a defining feature of our universe. Without this difference galaxies and planets could not form, and life could not exist. We think neutrinos may hold the key to understanding why it happened. Neutrinos, discovered almost a century ago, are the most evanescent of particles. They have no charge, barely interact with matter and were long thought to have no mass at all (like a photon). To detect them we have had to build enormous but very sensitive detectors. Our experiments show that neutrinos have a very small mass; it is this that might cause the preponderance of matter over anti-matter. An important part of our research is to make detailed measurements of neutrinos, to understand their masses and if they are responsible for our matter-dominated universe. The discovery of the Higgs particle marks a new era in our understanding. It confirms the existence of a fundamentally new entity that pervades all of nature and gives mass to elementary particles. Without the Higgs electrons could not bind to protons to make hydrogen atoms, and without atoms our universe would be a very different, lifeless place. In our experiments, we study the Higgs to measure and understand its behaviour. We are motivated by the fascinating possibility that the Higgs may help us understand the dark side of the universe; the mysterious dark matter. It has long been known that there are not enough stars visible in galaxies to explain the speed at which stars rotate around them. Our best explanation is that galaxies also contain massive, invisible (dark) matter which supplies the extra gravitational glue necessary to keep stars in their orbits. Calculations suggest this dark matter forms five times as much of the universe as the matter we see. The Higgs could interact with dark matter, giving us a way to illuminate the dark sector of the universe for the first time. Astrophysical observations also suggest that the Universe's expansion is accelerating, as if there is pressure created by space itself. How this happens is not yet understood, although it has been suggested that an unknown (dark) energy permeating the universe could cause the acceleration. Dark energy, together with dark matter, form 95% of the universe. In other words, we have only studied and understood 5% of the cosmos in our existing experiments. It is imperative that we understand more, and we have joined new experiments to investigate dark energy, discover new physics, and ultimately uncover the nature of the Universe.