Compton Streuung - Highly differential studies

康普顿散射是光与物质相互作用的基本过程之一，它是证明光的粒子性质的教科书范例。这个过程是一个（高能）光子和电子之间的台球式二元碰撞，其中光子偏转并将其部分能量和动量转移给电子。尽管康普顿散射具有基本和基本的性质，但它在今天仍然提出了许多悬而未决的问题，正如一篇关于该主题的综述的纲目标题“需要进一步测量x射线能量的非弹性散射”所强调的那样。有三种特别令人感兴趣的机制：首先，低光子能量和/或小动量转移的领域，其中电子的结合能与类似台球的碰撞场景所隐含的能量转移的顺序相同。其次，所有电子不能被视为独立粒子的过程，但相关性是必不可少的，第三，分子靶标领域。在当前的项目中，我们将讨论这三种制度。为此，我们将在单个原子和分子的气相上进行首次康普顿散射的重合实验。这些实验将在欧洲同步辐射设施（汉堡的“粉红”3号，格勒诺布尔的ESRF）进行，在那里，有足够的光子通量的所谓“粉红”光束（即绕过单色仪的光子光束）可以在极小的低截面上进行这种测量。我们将使用与申请者团队合作开发的COLTRIMS反应显微镜，以高分辨率和4π收集立体角测量康普顿散射产生的电子和离子的动量矢量。从这两个动量矢量，可以从动量守恒推导出散射光子的动量和能量传递。因此，从我们的实验中，我们将得到所有光子偏转角度和所有能量转移的各自的角度发射分布和弹出电子的能谱。在阿瑟·h·康普顿（Arthur H. Compton）的基本发现95年后，我们的实验将是第一个对自由原子或分子（气相）进行的研究，其中散射光子和被踢电子的动量和方向是巧合地确定的。这将为康普顿散射提供最详细和最完整的视图。因此，除了它们的教科书性质外，我们的重合气相实验将允许解决上述三种状态下康普顿散射的开放性问题。我们将在低能下进行研究，在低能下，束缚电子的康普顿散射被能量抑制，研究康普顿散射的情况，在这种情况下，电子-电子相关是必不可少的，并探索康普顿散射在分子中打破旋转对称的过程。

Compton scattering is one of the fundamental processes by which light interacts with matter, and it is the textbook example for demonstration of the particle nature of light. The process is a billiard type binary collision between a (high energy) photon and an electron, in which the photon is deflected and transfers part of its energy and momentum to the electron. Despite of its elementary and fundamental nature Compton scattering still poses major open questions today as emphasized by the programmatic title "Need for further inelastic scattering measurements at X-ray energies" of a review on the subject. There are three regimes, which are of particular interest: Firstly, the domain of low photon energies and/or small momentum transfers, where the binding energy of the electron is of the order of the energy transfer implied by the billiard-like collision scenario. Secondly, the regime of all processes in which electrons cannot be treated as independent particles, but the correlations are essential and, thirdly, the realm of molecular targets. It is these three regimes, which we will address, in the current project. To this end, we will perform the first ever coincidence experiments on Compton scattering on individual atoms and molecules in the gas phase. The experiments will be pursued at European synchrotron radiation facilities (PETRA3 in Hamburg, ESRF in Grenoble) where so called „pink“ beams (i.e. photon beams bypassing the monochromator) of sufficient photon flux are available for such measurements at extremely small low cross sections. We will use a COLTRIMS reaction microscope, co-developed by the group of the applicant, to measure the momentum vectors of electrons and ions created by Compton scattering with high resolution and 4π collection solid angle. From these two momentum vectors, the momentum and energy transfer of the scattered photon can be deduced from momentum conservation. Thus, from our experiment, we will obtain for all photon deflection angles and all energy transfers the respective angular emission distribution and energy spectrum of the ejected electron. Our experiments will be, 95 years after Arthur H. Compton’s fundamental discovery, be the first study in which for a free atom or molecule (gas phase) the momenta and directions of the scattered photon and the kicked electron are determined in coincidence. This will provide the most detailed and most complete view at Compton scattering ever achieved. Thus, besides their textbook character, our coincidence gas phase experiments will allow to address the open questions of Compton scattering in the afore mentioned three regimes. We will perform studies at low energies, where Compton scattering at a bound electron is energetically suppressed, investigate cases of Compton scattering, where electron-electron correlation is essential and explore Compton scattering in a molecule breaking the rotational symmetry of the process.