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

这个项目是代表ALPHA合作进行的，ALPHA合作是一个基于cern的合作，旨在捕获和研究反氢，以便能够将其特性与氢的特性进行比较，并更好地了解反物质的物理特性。这项研究的动机来自标准模型，该模型预测大爆炸后物质和反物质的数量相等。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构成。反氢是寻找物质和反物质之间差异的理想场所，因为现代理论和实验物理学给了我们对氢原子的深刻理解。到目前为止，ALPHA已经测量了反氢中1S-2S跃迁的共振频率[1]和线形[3]，并发现这两种性质与氢中的相同性质非常一致，并且目前正在构建一个名为ALPHA-g的实验设备的扩展，旨在测量反氢如何与重力相互作用。ALPHA通过在一个叫做Penning-Malmberg陷阱的带电粒子陷阱中分离其两个组成粒子——反质子和电子的等离子体，在一个叫做ALPHA-2的实验装置中产生并捕获反氢，该陷阱的描述见参考文献[4]。然后，反氢原子被困在一个浅层磁性最小中性阱中，该阱可以捕获温度低于0.54K的反原子。由于反氢原子通常在比α -2高得多的温度下产生，因此只有一小部分产生的反氢原子冷到足以被捕获。实际上，这意味着每一个循环产生大约3万个反氢原子，只有大约10个被捕获。这意味着每分钟大约有5个反原子。[2]中给出了这个过程的更详细的描述。提高这一捕获率将有利于未来由ALPHA进行的任何测量，因为它将允许更快地进行测量，允许在ALPHA可用来捕获反氢的有限时间内收集更多数据。该项目是基于研究一种提高反氢捕获率的方法，该方法涉及将激光冷却的[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+达到某种平衡温度。这已经在参考[6]的实验和参考[7]的模拟中得到了证明。有强有力的证据表明，在反氢形成过程中使用的正电子等离子体的温度会影响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多的反氢原子被捕获，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