Trapped Antihydrogen - Towards Spectroscopy

反氢，一个正电子和一个反质子的束缚状态，最近在实验室的受控条件下产生。该提议试图通过使用磁梯度陷阱来创造和捕获非常冷的反氢，以此为基础。这是一种磁场的排列，作用于反原子的小磁矩，产生捕获力。然而，这种陷阱很浅，目前只能容纳动能低于1开尔文的中性物质。为了有效地捕获反氢，它必须在这个温度或更低的温度下生产。这需要对我们的设备进行几次重大的更改和升级。这些措施包括一个全新的磁体和低温系统，一个用于中性陷阱的八极线圈布置，一个新的反氢湮没探测器，以及对正电子蓄电池性能的升级。这些变化本质上是非常技术性的，支持的详细理由试图解释它们并证明它们的合理性。然而，所有的反氢实验都是困难的，所以我们在这里要解决的问题是：为什么要费心呢？我们将用对称性的例子来解释这一点。很明显，根本的不对称性隐藏在自然界的深处。例如，在20世纪50年代的S发现，弱的核相互作用违反宇称守恒。然而，有缺陷的宇宙镜大部分可以通过添加所谓的电荷共轭来修复，粗略地说，这意味着当每个粒子被其反粒子取代时，相互作用不受影响。有一段时间，人们相信自然规律将遵循宇称反转和电荷共轭相结合的规律。但到了20世纪60年代中期，S发现，对于一小类被称为K介子的不寻常的、转瞬即逝的粒子的反应，这是不正确的。从那时起，人们一直认为电荷共轭/宇称反转镜中的小瑕疵可以通过应用时间反转来纠正。然而，这种三向开关不同于三个离散对称或它们的任意双向组合，因为电荷/宇称/时间组合作为一个定理存在，可以用量子场论的基本假设来证明。这些理论是我们目前对宇宙理解的基石，但被广泛认为是不完整的。因此，测试这种独特的三向开关是我们理解自然的核心。我们目前对宇宙起源的描述与大爆炸有关，大爆炸被认为是一个能量事件，创造了等量的物质和反物质。那么，为什么它们不都互相毁灭，留下一个没有物质的宇宙呢？在宇宙中寻找大量的残余反物质，都没有找到任何踪迹。目前，人们认为我们的宇宙是物质主导的，换句话说，是不对称的。另一个补充的事实是，我们目前通过大量对转瞬即逝的稀有粒子的研究所确定的不对称量不足以解释物质宇宙的存在。因此，对宇宙的演化还没有完全了解，这使得测试自然的对称性变得非常重要。冷反氢的产生数量适合研究，为对称性打开了一扇新的大门；希望这将允许与氢的光谱线进行精确的激光光谱比较。氢的光谱学最近已经达到了惊人的精度，特别是双光子的1S-2S跃迁，它已经被确定为大约一亿分之二。令人惊讶的是，由于质子性质的不确定性，这种精确度远远超过了理论所达到的水平。氢和反氢的比较不会有这种影响。我们的建议将有助于使这些比较成为现实。

Antihydrogen, the bound state of a positron and an antiproton, has recently been created under controlled conditions in the laboratory. The proposal seeks to build upon this by creating and trapping very cold antihydrogen using a magnetic gradient trap. This is an arrangement of magnetic fields that acts upon the small magnetic moment of the antiatom to produce a trapping force. However, such traps are shallow, and are currently only capable of holding neutral species with kinetic energies equivalent to a temperature below 1 Kelvin. To trap antihydrogen efficiently it must be produced at this temperature, or below. This requires several major changes and upgrades to our apparatus. These include a complete new magnet and cryogenic system, an octupole coil arrangement for the neutral trap, a new antihydrogen annihilation detector and upgrades to the performance of the positron accumulator. These changes are very technical in nature and the detailed case for support seeks to explain and justify them. However, all experiments with antihydrogen are difficult, so the question we address here is; why bother? We will explain this using the example of symmetry.It has been apparent for a while that fundamental asymmetries are hidden deep within nature. For example, in the 1950's it was discovered that the weak nuclear interaction violates parity conservation. However, the defective parity mirror can be mostly repaired by adding so-called charge conjugation, which, loosely speaking, means that interactions are unaffected when every particle is substituted by its antiparticle. For a while it was believed that the laws of nature would obey the combination of parity reversal and charge conjugation. But by the mid-1960's this was found to be untrue for a small class of reactions involving unusual, fleeting, particles called K-mesons. Since then it has been assumed that the small blemish in the combined charge conjugation/parity reversal mirror can be corrected by the application of time-reversal.However, this 3-way switch differs from the three discrete symmetries, or any 2-way combination of them because the charge/parity/time combination exists as a theorem that can be proved using the basic postulates of quantum field theory. Such theories are the cornerstone of our current understanding of the Universe, but are widely recognised as being incomplete. So testing this unique 3-way switch is going to the heart of our understanding of nature. Our current picture of the beginning of the Universe involves the Big Bang, which is thought to have been an energetic event that created equal amounts of matter and antimatter. Why then did they not all annihilate one another and leave a Universe devoid of matter? Searches for large amounts of remnant antimatter in the Universe, have failed to find any trace. Currently it is thought that our Universe is matter dominant; in other words asymmetric. The other fact to add to this is that the amount of asymmetry we can currently identify via numerous studies of fleeting and rare particles isn't enough to explain the existence of the material Universe.Thus, the evolution of the Universe is not fully understood and this makes testing the symmetries of nature of great importance. The creation of cold antihydrogen in amounts suitable for study, has opened a new door on symmetry; hopefully one which will allow precision laser spectroscopic comparisons with the spectral lines of hydrogen. Spectroscopy of hydrogen has recently reached fantastic precision for one line in particular, the two-photon 1S-2S transition, which has been determined to about 2 parts in a hundred million million. Amazingly, due to uncertainties in the properties of the proton, this level of precision is way beyond that achieved by theory. Comparisons of hydrogen and antihydrogen would be free of this effect. Our proposal will help make these comparisons a reality.