Antiparticle beamline for experiments on matter antimatter symmetry

在今天的宇宙中，反物质的缺失和物质的优势仍然是物理学面临的最大难题之一。早在1967年，著名的萨哈罗夫条件就描述了这个不对称宇宙是如何通过要求物质和反物质之间的对称违反（即差异）来产生的。到目前为止，还没有发现足够的对称性违反来解决这个问题，因此这个谜题仍然存在。这个项目旨在通过直接测试由反物质组成的原子与它们的物质对应物无法区分的假设来寻找这个问题的答案。这笔拨款提议建造一条光束线，这将提高现有设备的性能，并使ALPHA反氢实验得以显著扩展。在这个项目中，我们已经开始应用最先进的精密测量工具来解决这个问题。我们的方法是捕获反氢原子（由反质子和正电子组成的原子），并使用原子物理学的光谱技术研究它们的内部状态，同样的技术给了我们原子钟，全球定位系统（GPS）的基础，以及迄今为止人类工具箱中最精确的仪表。具体来说，（ALPHA-2）我们将研究磁阱中反氢从基态到第一激发态的转变，以测试这种转变的频率与氢（物质）的频率完全相同的假设。对氢的这种转变的研究精度达到了惊人的小数点后15位。在这个项目中，我们计划成为第一个研究反氢的这种转变的人，期望这个初始实验的精度在小数点后10位左右。在这个项目的第二个线索（ALPHA-g）中，我们利用我们在反氢俘获方面的专业知识来执行教科书测量反物质的引力加速度。这是一项壮举，因为我们可以使用电荷中性的反氢：由于静电相互作用的大小淹没了所有引力效应，导致系统误差，因此没有对带电粒子进行引力加速度的测量。虽然上面讨论的基本对称性都要求反氢与氢是相同的，并且宇宙中有等量的物质和反物质（因此是难题），但引力问题具有不同的性质。我们目前对引力的理解依赖于爱因斯坦的广义相对论，该理论基于惯性（运动）质量等于引力质量的假设。这个公设称为弱等效原理。如果我们对引力的理解是正确的，那么一定质量的反物质也应该遵循这一原则。因此，通过实验验证这一原理对我们进一步了解引力具有极大的意义。这个项目中的反物质研究测试了物理学的基础，经过几十年的成功，这些基础让我们对物理世界有了很多了解。尽管取得了这些成功，我们仍然不明白为什么宇宙中似乎没有大块反物质。在这个项目中，我们应用最精确的物理工具，寻找与我们目前理解的微小偏差。过去的经验表明，对自然的仔细观察是取得突破的途径，而反氢性质是引人注目的主题，因为它们的值的预测非常具体，迄今尚未得到验证。在这条道路上找不到线索的风险（尽管没有线索当然意味着排除一些可选的解释，因此并非毫无兴趣），被反氢和氢之间的任何测量差异所暗示的壮观和不可量化的后果所抵消。

The virtual absence of antimatter and preponderance of matter in the Universe today remains one of the biggest conundrums facing physics. Already in 1967, the famous Sakharov conditions described how this asymmetric Universe could come about by requiring symmetry violations (i.e. differences) between matter and antimatter. Until now, no sufficient symmetry violations have been found to resolve this question, thus the puzzle remains. This project aims to seek answers to this question by directly testing the supposition that atoms made of antimatter are indistinguishable from their matter counterparts.This grant proposes the construction of a beamline which will improve the performance of the existing apparatus and enable significant expansion of the ALPHA antihydrogen experiment. In this project we have set out to apply the greatest tools of precision measurements to this problem. Our approach is to trap antihydrogen atoms, (atoms made of antiprotons and positrons), and study their internal states using spectroscopic techniques from atomic physics, the same techniques that have given us atomic-clocks, the basis for the global positioning system (GPS) and the most precise gauges in the human toolbox to date. Specifically, (ALPHA-2) we will investigate the ground to first excited state transition in antihydrogen held in a magnetic trap to test the hypothesis that the frequency of this transition is exactly the same as that of hydrogen (matter). This transition has been investigated with a staggering 15 decimal places of precision in hydrogen. In this project we plan to be the first to investigate this transition in antihydrogen, expecting around 10 decimal places of precision for this initial experimentIn the second thread of this project (ALPHA-g) we exploit our expertise in antihydrogen trapping to perform a text book measurement of the gravitational acceleration of antimatter. This is a feat that is only possible because we can use charge neutral antihydrogen: no measurements of gravitational acceleration have been accomplished on charged particles due to systematic errors arising from the size of electrostatic interactions that swamp all gravitational effects. While the fundamental symmetries discussed above both require that antihydrogen is identical to hydrogen and that there are equal amounts of matter and antimatter in the Universe (hence the conundrum), the gravitational question is of a different nature. Our current understanding of gravity relies on Einstein's general theory of relativity, which is based on the postulate that inertial (movement) mass is equal to gravitational mass. This postulate is called the weak equivalence principle. A given mass of antimatter should also obey this principle if our understanding of gravity is correct. Testing this principle experimentally is therefore of great interest to further our knowledge of gravity.The antimatter research in this project tests the very foundations of physics, foundations that have, through decades of success, given us many insights into the physical world. In spite of these successes, we still do not understand why there appears to be no bulk antimatter in the Universe. In this project we apply the most precise tools available to physics, to look for tiny deviations from our current understanding. Past experience demonstrates that careful observation of Nature is the way to make breakthroughs and antihydrogen properties are compelling subjects because of the very specific and thus far untested predictions of their values. The risk of finding no clues on this path (though no clues would of course mean the exclusion of some optional explanations, and so are not devoid of interest) is outweighed by the spectacular and unquantifiable consequences any measured difference between antihydrogen and hydrogen would imply.