Consolidated Grant 2015

实验粒子物理小组的研究解决了基础物理中的一些主要问题。最紧迫的问题之一是，宇宙中物质压倒反物质的压倒性优势背后的机制是什么？物质和反物质在早期宇宙中应该是等量产生的，然而它们自然发生的巨大差异是我们观察到的一个决定性特征。没有这种不对称性，生命就不可能存在。我们认为，中微子可能是理解物质-反物质不对称性的关键。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，长期以来被认为是完全无质量的(就像光子一样)。它们可以在地球上穿行，但留下痕迹的可能性微乎其微。为了探测中微子，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，中微子实际上有一个非常小但明显不为零的质量。这种小的非零质量允许它们在早期宇宙中驱动物质-反物质的不对称性。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，并计算它们的性质是否确实是解释物质-反物质占主导地位所需的那些性质。希格斯粒子的发现是过去十年中最重要的发现之一。它证实了一种全新类型的“力”的存在，这种“力”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，像电子这样的粒子就不能与质子结合来制造氢原子。因此，正常的原子物质，甚至恒星，都不可能形成。我们继续研究希格斯粒子，以测量和理解它的性质。我们特别感兴趣的是，希格斯粒子是否为我们所说的“暗宇宙”提供了一扇窗口。人们早就知道，宇宙中没有足够的可见物质来解释星系自转的速度。根本没有足够的恒星。唯一的解释似乎是，在我们周围，在所有的星系中，都有一个无形的物质光环，它施加了引力影响(因此星系的自转速度如此之快)，但它不与光相互作用。计算表明，宇宙中这种暗物质的数量是可见物质的5倍。希格斯粒子可以与暗物质相互作用，因此我们可以第一次使用希格斯粒子来“照亮”暗扇区。这是我们研究的一个重要部分。观测还表明，宇宙正在膨胀，就好像有空间本身产生的压力。这个过程是可以观察到的，但不是很清楚。它强烈地表明，还有另一种形式的暗能量在起作用。总体而言，暗宇宙占宇宙中95%的物质/能量，只有5%(我们可以观察到)是发光的。这使得对暗物质和能量的研究对我们理解我们世界的根本性质来说是绝对重要的。因此，我们加入了旨在尝试、研究和揭示暗能量的真实本质的实验。我们关于所有粒子如何相互作用的理论体现在所谓的标准模型中。除了中微子及其质量之外，它具有巨大的预测能力，并为阐明宇宙的本质提供了一个简单的框架。遵循科学的方法，我们继续在能量前沿改进和测试SM，并进行专门的精密实验。这为新物理学的发现提供了另一条经过充分检验的途径。

The research of the experimental particle physics group addresses some of the main questions in fundamental physics. One of the most pressing is what is the mechanism that is behind the overwhelming dominance of matter over anti-matter in the Universe? Matter and anti-matter should have been created in equal quantities in the early Universe, yet the gross difference in their natural occurrence is a defining feature of what we observe. Without this asymmetry life could not exist. We believe that neutrinos may hold the key to understanding the matter-antimatter asymmetry. 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 be completely massless (like a photon). They can travel through the earth with only the tiniest probability of leaving a trace. To detect neutrinos we have had to build enormous but very sensitive detectors. Our experiments show that neutrinos actually have a very small but significantly non-zero mass. This small non-zero mass allows them to drive the matter-antimatter asymmetry in the early Universe. An important part of our research is to make detailed measurements of the neutrinos, to understand their masses and to calculate if their properties are indeed those required to explain the matter-antimatter dominance.The discovery of the Higgs particle was one of the most important in the last decade. It confirmed the existence of a fundamentally new type of "force" that pervades all of nature and gives mass to elementary particles. Without the Higgs, particles such as electrons could not bind to protons to make hydrogen atoms. Thus normal atomic matter, even stars, could not be formed. We continue to study the Higgs to measure and understand its properties. We are especially interested to see if the Higgs particles provides a window to what we call the "dark universe". It has long been known that there is not enough visible matter in the Universe to explain the speed at which galaxies rotate. There are simply not enough stars. The only explanation appears to be that surrounding us, and in all galaxies, there is a halo of invisible matter which exerts a gravitational influence (hence why the galaxies spin as fast as they do) but which does not interact with light. Calculations suggest there is 5 times more of this dark matter than visible matter in the Universe. The Higgs could interact with dark matter, thus we can use the Higgs to "illuminate" the dark sector for the first time. This is an important part of our research. Observations also suggest that the Universe is inflating, as if there is pressure created by space itself. This process is observed but non-understood. It strongly suggests there is another form of dark energy at work. Altogether the dark universe accounts for 95% of the matter/energy in the Universe with only 5% (that we can observe) being luminous. This makes the study of the dark matter and energy absolutely central to our understanding of the fundamental nature of our world. Thus we have joined experiments whose aim is to try and study and uncover the true nature of dark energy.Our theory of how all particles interact is embodied in what is called the Standard Model. With the exception of neutrinos and their masses it has enormous predictive power and provides a simple framework for elucidating the nature of the universe. Following the scientific method we continue to refine and test the SM at the energy frontier and with dedicated precision experiments. This provides another, and well tested route, to the discovery of new physics.