Widening the search for Dark Matter and Physics beyond the Standard Model with direct detection experiments

我们在宇宙中所能看到的一切只是其质量的一小部分。其中大部分是“黑暗”的，高达令人难以置信的85%--而我们对此知之甚少。我们可以推断这种神秘的“暗物质”在早期宇宙中的作用，当时它允许星系形成，我们今天可以观察到它的引力效应，因为它将包括我们自己的星系在内的星系聚集在一起。然而，我们不能直接看到它，也还没有做出任何检测来帮助我们理解它的性质。简单地说，我们知道暗物质在那里，但我们不知道它是什么！我们所知道的是，粒子物理的标准模型如此准确地解释了我们所观察到的大多数东西，但它并不能帮助我们--它没有提供符合条件的候选者。暗物质的探测不仅将告诉我们我们宇宙的大部分是由什么组成的，它还将打开超越标准模型的物理学之门，揭开我们之间的面纱，加深对宇宙以及我们在其中的位置的理解。探测暗物质的努力是全世界的--这确实是我们这个时代最重要的科学任务之一。综合所有证据，我们最好的理论告诉我们，暗物质是由弥漫在宇宙中但很少相互作用的微小粒子组成的--当你阅读这篇文章时，数以百万计的暗物质粒子正在无害地穿过你的身体。只是偶尔，它们中的一个可能会从原子核反弹，给它一点能量。观察这种“直接”的散射是确保我们已经看到了来自我们银河系的暗物质的唯一方法；暗物质诞生于大爆炸中，并且从此以后一直存在。但要有希望看到如此微小、罕见的信号，需要进行不同于其他任何实验的实验：大型探测器，对单个原子的反冲敏感，由最具放射性纯度的材料建造，深埋在地球表面下。LUX-ZEPLIN(LZ)将是有史以来在直接搜索暗物质方面建立的最大、最先进的实验。LZ将于2019年上线，在美国南达科他州地下1.5公里处的一个前金矿改造的科学实验室中运行3年。我是LZ实验的主要研究员，负责帮助我们设计它的模拟；对标准模型过程中可能掩盖暗物质特征的“背景”水平进行建模；以及建立该实验的科学覆盖范围。LZ的灵敏度将是之前实验的10倍以上，其前所未有的规模和超低背景环境将预示着直接搜索的新纪元。除了探索剩余的大部分未知领域以寻找最受欢迎的暗物质候选者--弱相互作用大质量粒子(WIMP)之外，LZ现在将对一大批同样动机良好的替代(非WIMP)暗物质候选者和标准模型以外的其他物理学具有敏感性和发现潜力。这些搜索的关键是我在建模背景过程、利用LZ可用的全能量范围内的多个信号通道以及开发软件以识别来自完全意想不到的物理的复杂信号方面的专业知识。我将在WIMP和LZ的替代模型搜索中发挥领导作用，以发现突破性的发现。除了物理分析和软件，我还在英国开发了新的硬件功能，具有世界级的质谱学，可以测量材料中的痕量放射性。这项技术对于建立任何未来的实验至关重要，这些实验需要确认发现，执行高精度的信号测量，或者探索WIMP可用的最后一个参数空间。这样的实验将对其他模型具有难以置信的敏感性，并超越标准模型物理学，例如无中微子的双贝塔衰变。我的质谱学研究将满足下一代实验对放射性纯度的严格要求，并提供所有科学所依赖的背景模型。

Everything we can see in the Universe is only a small fraction of its mass. Most of it, an incredible 85%, is 'dark' - and we know remarkably little about it. We can infer the role of this mysterious 'Dark Matter' in the early Universe when it allowed galaxies to form and we can observe its gravitational effects today as it holds the galaxies, including our own, together. Yet we cannot see it directly and have yet to make any detection that helps us understand its nature. Put simply, we know Dark Matter is there, but we do not know what it is! What we do know is that the Standard Model of particle physics that explains so accurately most of what we do observe cannot help us - it provides no candidates that fit the bill. The detection of Dark Matter will not only tell us what much of our Universe is made of, it will also open the door to physics beyond the Standard Model, bringing down the veil between us and a deeper understanding of the Universe and our place within it. The effort to detect Dark Matter is worldwide - it is truly one of the most important scientific missions of our time.Piecing together all the evidence, our best theories tell us Dark Matter is made up of tiny particles that that pervade the Universe but rarely interact - millions of Dark Matter particles are passing harmlessly through you as you read this right now. Just occasionally one of them may bounce off the nucleus of an atom, giving it a tiny kick of energy. Observing such a 'direct' scatter is the only way to be sure that we have seen Dark Matter from our own galaxy; born in the Big Bang and present ever since. But to have any hope of seeing such tiny, rare signals requires experiments like no other: large detectors, sensitive to the recoil of a single atom, constructed from the most radio-pure materials and buried deep under the surface of the Earth.LUX-ZEPLIN (LZ) will be the largest and most advanced experiment ever built in the direct search for Dark Matter. LZ will come online in 2019 and operate for 3 years in a former gold mine turned science laboratory 1.5 km underground in S. Dakota, USA. I am a leading researcher in the LZ experiment, responsible for the simulations that helped us to design it; that model the level of 'background' from Standard Model processes that may mask Dark Matter signatures; and that establish the experiment's science reach. LZ will be over 10 times more sensitive than earlier experiments and its unprecedented scale and ultra-low background environment will herald a new era in direct searches. In addition to exploring the bulk of the remaining uncharted territory in search of Weakly Interacting Massive Particles (WIMPs), the most popular candidate for dark matter, LZ will now have sensitivity and discovery potential to a whole host of equally well-motivated alternative (non-WIMP) Dark Matter candidates and other physics beyond the Standard Model. Key to these searches is my expertise in modelling background processes, in exploiting multiple signal channels across the full energy range available to LZ, and in developing software to recognise complex signals from wholly unexpected physics. I will take leading roles in the WIMP and alternative model searches from LZ to uncover groundbreaking discoveries.Alongside physics analyses and software, I have developed new hardware capability in the UK with world-class mass-spectrometry to measure trace radioactivity in materials. This technique is crucial to building any future experiment needed to confirm discovery, perform high-precision measurements of signal, or explore the last of the available parameter space available for WIMPs. Such an experiment would have incredible sensitivity to the alternative models and beyond Standard Model physics, such as neutrino-less double beta decay. My mass-spectrometry research will meet the stringent radio-purity needs for future generation experiments and feed the background model upon which all the science rests.