Precision Experiments with Antihydrogen

粒子宇宙目前主要由物质组成的观察似乎是明确的，正如宇宙诞生时包含等量的物质和反物质的断言一样。为什么会出现这种不平衡或不对称，目前还不清楚，事实上，这是物理学的核心问题之一，超出了所谓的标准模型。在基础物理学中，传统的实验探索对称性的方法是研究粒子在更高动能下的碰撞，试图重现宇宙开始（大爆炸）时的条件。然而，越来越清楚的是，这种研究可以通过小规模实验来补充和丰富，例如在设定粒子电偶极矩的限制方面，通过新的暗物质搜索，以及，如这里，在物质和反物质性质的精确比较中，我们选择了通过原子捕获和冷却物理学以及原子光谱学开发的强大工具箱来承担这一点。问题.简而言之，我们先创造、捕获反氢原子，然后冷却，再研究它们的性质和行为。在一组实验（ALPHA-III，这将致力于光谱研究），我们打算系统地探测反原子的基态和它的第一个激发态之间的过渡使用被称为双光子多普勒无光谱技术。我们希望能以类似于目前氢原子的精度来确定它的频率，氢原子的精确度是惊人的小数点后14位。这将提供一个非常直接的对称性测试。我们已经测量了反氢原子的相同跃迁，精确到小数点后12位，现在我们的目标是氢原子的精确度。此外，我们打算通过结合基态到第一激发态的工作和对额外跃迁的光谱测量来确定反原子中的基本常数，例如反里德伯常数和反质子电荷半径。我们将分析反氢原子的轨迹，因为它们离开了一个目的，建造原子阱，其磁场经过精心设计，以提高对反原子引力行为的实验灵敏度。我们希望首次确定反物质因重力而加速。最终，我们希望反氢原子的g值能精确到1%或更高。对（反）原子系统上引力行为的兴趣部分源于现代物理学的另一个难题，即我们的引力理论（爱因斯坦的广义相对论）与目前公认的量子场论不相容。虽然等效原则规定，所有对象，无论其内容（例如，在这种情况下，无论它们是由物质还是反物质组成），都应该以相同的加速度落向地球，测试量子物体上的（经典）引力理论具有根本意义。电中性的反物质系统是最好的，因为它们不受电场的影响，电场可以淹没带电粒子的引力效应，而反氢是特别合适的，因为它现在可以被捕获和冷却。因此，我们通过探索反氢物理学来双管齐下地攻击对称性和引力，有望为自然界提供新的见解。我们确定反物体的性质和行为的能力是前所未有的，我们的目标是通过本提案中提出的工作进一步发展这一点。物质和反物质之间的任何差异，无论多么微小，都会对我们理解物理学和自然定律产生深远的影响。

The observation that the particulate Universe is currently comprised mostly of matter seems unequivocal, as does the assertion that at its birth, the Universe contained equal amounts of matter and antimatter. Just why this imbalance, or asymmetry, has evolved is currently not understood, and indeed it is one of the central questions of physics beyond what is known as the Standard Model. The conventional approach to experimentally explore symmetry in fundamental physics is to study particle collisions at ever-higher kinetic energies, in an effort to reproduce conditions further back towards the beginning of the Universe (the Big Bang). It is becoming increasingly clear, though, that such investigations can be complemented and enriched via small scale experiments, for instance in setting limits on particle electric dipole moments, with novel dark matter searches and, as here, in precision comparisons of the properties of matter and antimatter.We have chosen to bring the powerful toolbox developed via the physics of atom trapping and cooling and atomic spectroscopy to bear on this problem. In short, we create, capture and then cool antihydrogen atoms before studying their properties and behaviour. In one set of experiments (ALPHA-III, which will be devoted to spectroscopic investigations) we intend to systematically probe the transition between the ground state of the anti-atom and its first excited state using a technique known as two-photon Doppler-free spectroscopy. We hope to determine its frequency with a precision similar to that currently achieved for the hydrogen atom, for which it is known to a staggering 14 decimal places. This will deliver a very direct test of symmetry. We have already measured the same transition in antihydrogen to 12 decimal places and we are now aiming for the hydrogen precision. Additionally, we intend to determine fundamental constants in anti-atoms, such as the anti-Rydberg constant and the antiproton charge radius, by combining the ground-to-first excited state work with spectroscopic measurements of additional transitions.In our second major experimental avenue, so-called ALPHA-g, we will analyse the trajectories of antihydrogen atoms as they leave a purpose-built atom trap whose magnetic fields have been carefully tailored to enhance experimental sensitivity to the gravitational behaviour of the anti-atom. We expect to make the first determination of the acceleration of antimatter due to gravity. Eventually we hope to extract the value of g for antihydrogen to an accuracy of 1% or better. Interest in the behaviour of gravity on (anti-)atomic systems stems in part from another puzzle of modern physics, namely that our theory of gravity (Einstein's General Relativity) is incompatible with currently accepted quantum field theories. And whilst the equivalence principle dictates that all objects, irrespective of their content (e.g., in this context independently of whether they are comprised of matter or antimatter), should fall with the same acceleration towards the Earth, testing the (classical) theory of gravity on quantum objects is of fundamental interest. Electrically neutral antimatter-systems are preferable, since they are immune to the influence of electric fields, which can swamp the effects of gravity for charged particles, and antihydrogen is particularly suitable, since it can now be trapped and cooled.Thus, our two-pronged attack on symmetry and gravity by exploring the physics of antihydrogen promises the development of new insights into nature. Our ability to pin down the properties and behaviour of anti-objects is unprecedented, and we aim to further develop this with the work set out in this proposal. Any difference between matter and antimatter, however small, will have profound consequences for our understanding of physics and the laws of nature.