Slow Neutral Antimatter Atoms in Excited States for Inertial-type Precision Measurements (SNAP)

欧洲核子研究中心的反质子减速器（AD）设施于2000年投入使用，是目前世界上唯一允许实现低能反质子束实验的设施。它导致了冷反氢的成功生产，这在科学界和公共媒体中得到了广泛的认可。反氢的成功长期储存被物理世界选为2010年的顶级物理亮点。其他最近的突破包括用于飞行超精细光谱学的反氢的产生，反氢电荷异常的直接测量，捕获反氢中1 S-2S跃迁的观察及其表征，反氢中1 S-2 P莱曼α跃迁的观察，新型冷却技术的演示，反质子与质子荷质比的精确测量，研究了超流4 He中反质子氦的高分辨激光共振。这里提出的项目SNAP旨在为尖端的反物质物理研究开发中性反物质原子的慢束。位于AD的AEgIS合作的主要目标是首次直接测量重力对反氢的影响。假设自由落体的普适性、弱等效原理或CPT不变性（在反物质的情况下）的有效性的间接界限将异常引力行为限制到只有精确测量才能操作的水平。反之亦然，足够精确的反物质实验对于验证这些基本假设至关重要。通过创建具有几微米厚度的纳米结构硅膜，几何优化的正电子-正电子素转换器将用于在低温超高真空环境中有效地形成Ps束。利用AEgIS的两个已建立的激光系统进行Ps激发，然后我们将首次尝试Ps激光冷却。激光冷却的成功应用将使我们能够创造出世界上最冷的Ps光束，具有出色的强度。该束将立即应用于两个雄心勃勃的研究议程：第一个是AEgIS的旗舰目标，即在来自新的ELENA设施的冷反质子和AEgIS的强冷Ps束之间进行电荷交换反应，以创建具有前所未有强度的反氢脉冲源。第二部分是对激发态中性Ps原子通过物质光栅的系统研究。这种光栅是所谓的莫尔偏转仪的中心部件，本质上是在经典状态下工作的原子干涉仪。偏转仪能够检测中性原子的位移，由于重力与所需的精度，主要的不确定性是光栅的表面偶极电位的影响。因此，我们应用我们的冷Ps光束来研究中性激发原子上的物质光栅的范德华力的影响，利用物质-反物质复合系统的独特性质，在明确定义的时间后或碰撞成其签名湮灭粒子后湮灭，携带与光栅相互作用的信息。

The Antiproton Decelerator (AD) facility at CERN became operational in 2000 and is presently the only facility in the world to allow the realization of experiments with low energy antiproton beams. It has led to the successful production of cold antihydrogen, which has been widely acknowledged in the scientific community, as well as in the public media. The successful storage of antihydrogen over an extended period was selected as top physics highlight in 2010 by physics world. Other more recent breakthroughs include the production of antihydrogen for in-flight hyperfine spectroscopy , direct measurements into the antihydrogen charge anomaly , observation of the 1S-2S transition in trapped antihydrogen and its characterization, the observation of the 1S-2P Lyman-alpha transition in antihydrogen, the demonstration of novel cooling techniques, the precise measurement of the antiproton-to-proton charge-mass ratio, and studies into high-resolution laser resonances of antiprotonic helium in superfluid 4He. The here-proposed project SNAP aims at developing slow beams of neutral antimatter atoms for cutting-edge antimatter physics research. The AEgIS collaboration, located at the AD, has the primary goal to directly measure, for the first time, the effect of gravity on antihydrogen with significant precision. Indirect bounds that assume the validity of, for example, the universality of free fall, the Weak Equivalence Principle or the CPT invariance also in the case of antimatter constrain an anomalous gravitational behaviour to a level where only precision measurements can operate. Vice versa, antimatter experiments with sufficient precision are essential to validate these fundamental assumptions. By creating nanostructured silicon membranes with few micrometer thickness, a geometrically optimized positron-to-positronium converter will be used to efficiently form a Ps beam in cryogenic UHV environments. Making use of AEgIS' two established laser systems for Ps excitation, we will then attempt Ps laser cooling for the first time. The successful application of laser cooling will enable us to create the world-wide coldest Ps beam with an outstanding intensity. This beam will be immediately applied to two ambitious research agendas:The first is AEgIS' flagship goal to perform the charge exchange reaction between cold antiprotons from the new ELENA facility and AEgIS' intense cold Ps beam to create a pulsed source of antihydrogen with unprecedented intensity. The second is the systematic study of excited neutral Ps atoms passing through a matter grating. Such gratings are the central piece of a so-called Moire deflectometer, essentially an atomic interferometer operating in the classical regime. The deflectometer enables the detection of the displacement of neutral atoms due to gravity with the required precision, the main uncertainty being the influence of the grating's surface dipole potentials. We thus apply our cold Ps beam to study the effect of van-der-Waals forces of the matter grating on neutral excited atoms, exploiting the unique property of the matter-antimatter compound system to annihilate after a well-defined time or upon collision into its signature annihilation particles, carrying information about the interaction with the gratings.