Towards Increased Antihydrogen Trapping Rates In The Alpha Experiment Using Sympathetically Laser Cooled Positrons

这个项目是代表阿尔法合作进行的，阿尔法合作是一个基于欧洲核子研究中心的合作，它捕获和研究反氢，以便能够将其性质与氢的性质进行比较，并更好地了解反物质的物理学。这项研究的动机来自标准模型，该模型预测了大爆炸后等量的物质和反物质。这与我们在宇宙中观察到的情况不一致，宇宙几乎完全由物质组成。由于现代理论和实验物理学对氢原子的深入理解，反氢是寻找物质和反物质之间差异的理想场所。迄今为止，阿尔法已经测量了反氢中1 S-2S跃迁的共振频率[1]和线形[3]，发现这两种性质与氢的相同性质非常一致，目前正在建造一个名为ALPHA-g的实验装置的扩展，该装置旨在测量反氢如何与重力相互作用。ALPHA在一个名为ALPHA-2的实验装置中产生并捕获反氢，方法是将反氢的两个组成粒子（反质子和电子）的等离子体隔离在一个名为潘宁-马尔姆伯格陷阱的带电粒子陷阱中，在参考文献[4]中给出了其描述。然后反氢原子被捕获在一个浅磁最小中性陷阱中，该陷阱可以捕获温度低于0.54K的反原子[4]。由于反氢原子通常是在比阿尔法-2高得多的温度下产生的，所以只有一小部分产生的反氢足够冷而被捕获。实际上，这意味着在每一个周期中，大约有30，000个反氢原子产生，只有大约10个被捕获。这相当于每分钟大约5个反原子。在[2]中给出了该过程的更详细描述。提高该捕获速率将有利于ALPHA将来进行的任何测量，因为它将允许更快地进行测量，从而允许在ALPHA可用于捕获反氢的有限时间内收集更多数据。该项目基于研究一种提高反氢捕获率的方法，该方法包括将激光冷却的[5] Be+离子等离子体引入用于反氢形成的正电子等离子体中。Be+离子可以被激光冷却到非常低的温度，同时保持在Be+和正电子的混合等离子体中。然后正电子将通过与Be+的库仑相互作用冷却，并与Be+达到某个平衡温度。这已经在参考文献[6]中通过实验和参考文献[7]中通过模拟得到了证明。有强有力的证据表明，用于反氢形成的正电子等离子体的温度会影响所产生的反氢原子的数量和反氢原子的最终温度，这意味着更冷的正电子等离子体将导致更大数量的反氢原子被捕获，可能是数量级的。EPSRC研究领域：反氢

This project is being undertaken on behalf of the ALPHA collaboration, a CERN-based collaboration that traps and studies antihydrogen in order to be able to compare its properties to those of hydrogen and gain a better understanding of the physics of antimatter. The motivation for this study comes from the Standard Model, which predicts equal amount of matter and antimatter after the Big Bang. This is at odds with what we observe in the universe, which is made almost entirely of matter. Antihydrogen is the ideal place to search for differences between matter and antimatter due to the depth of understanding that modern theoretical and experimental physics have given us of the hydrogen atom.ALPHA has so far measured the resonance frequency [1] and lineshape [3] of the 1S-2S transition in antihydrogen, and found both properties to be in good agreement with the same properties in hydrogen, and is currently constructing an extension to their experimental apparatus called ALPHA-g, which aims to measure how antihydrogen interacts with gravity.ALPHA creates and traps antihydrogen in an experimental apparatus called ALPHA-2 by isolating plasmas of its two constituent particles, the antiproton and the electron, in a charged particle trap called a Penning-Malmberg trap, a description of which is given in ref. [4]. Antihydrogen atoms are then trapped in a shallow magnetic minimum neutral trap which can trap antiatoms with a temperature less than 0.54K [4]. Since antihydrogen atoms are typically produced with a much higher temperature than this in ALPHA-2, only a small fraction of the antihydrogen produced is cold enough to be trapped. Practically, this means that for every cycle, where around 30,000 antihydrogen atoms are produced, only around 10 are trapped. This translates to around 5 antiatoms per minute. A more detailed description of this process is given in [2].Improving this trapping rate would be beneficial to any future measurements performed by ALPHA, since it would allow measurements to be made more quickly, allowing for more data to be gathered in the limited time that ALPHA has available for trapping antihydrogen. This project is based on investigating a method of increasing antihydrogen trapping rate that involves introducing a plasma of laser cooled [5] Be+ ions into the positron plasma used for antihydrogen formation. The Be+ ions can be laser cooled to very low temperatures whilst being held in a mixed plasma of Be+ and positrons. The positrons will then cool via Coulomb interactions with the Be+ and reach some equilibrium temperature with the Be+. This has been demonstrated experimentally in ref. [6] and via simulation in ref. [7]. There is strong evidence that the temperature of the positron plasma used in antihydrogen formation affects both the number of antihydrogen atoms produced and the final temperature of the antihydrogen atoms, meaning that a colder positron plasma will lead to larger numbers of antihydrogen atoms trapped, potentially by orders of magnitude.EPSRC Research Area: Antihydrogen