Trapped Antihydrogen - Towards Spectroscopy

反氢，一个正电子和一个反质子的结合状态，最近在实验室的受控条件下被创造出来。该提案试图在此基础上，利用磁梯度阱创造并捕获非常冷的反氢。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，目前只能容纳动能相当于温度低于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产生。这需要对我们的设备进行几项重大更改和升级。其中包括一个全新的磁铁和低温系统，一个中性陷阱的八极线圈安排，一个新的反氢湮灭探测器和升级的正电子蓄能器的性能。这些变化在本质上是非常技术性的，详细的支持案例试图解释和证明它们的合理性。然而，所有的反氢实验都很困难，所以我们在这里要解决的问题是；何苦呢?我们将用对称的例子来解释这一点。很明显，一段时间以来，基本的不对称隐藏在大自然深处。例如，在20世纪50年代，人们发现弱核相互作用违反宇称守恒。然而，有缺陷的宇称镜大多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都被它的反粒子取代时，相互作用不会受到影响。有一段时间，人们相信自然定律会服从宇称反转和电荷共轭的结合。但到了20世纪60年代中期，人们发现，对于一小类涉及罕见的、转瞬即逝的粒子k介子的反应来说，这是不正确的。从那时起，人们就假设复合电荷共轭/宇称反转镜中的小缺陷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种离散对称，或者它们的任何双向组合，因为电荷/奇偶性/时间组合作为一个定理存在，可以使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。所以测试这种独特的三向开关是我们对自然理解的核心。我们目前对宇宙起源的理解涉及到大爆炸，大爆炸被认为是一个能量事件，产生了等量的物质和反物质。那么，为什么它们没有彼此湮灭，留下一个没有物质的宇宙呢？对宇宙中大量残余反物质的搜索，未能找到任何痕迹。目前，人们认为我们的宇宙是物质主导的；换句话说就是不对称。另一个需要补充的事实是，我们目前通过大量对稍纵即逝的稀有粒子的研究发现的不对称性，还不足以解释物质宇宙的存在。

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.