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，也是证明光的粒子性质的教科书范例。这个过程是(高能)光子和电子之间的台球式二元碰撞，其中光子被偏转，并将其部分能量和动量传递给电子。尽管康普顿散射具有基本和基本的性质，但正如一篇关于该主题的综述的纲领性标题“需要在X射线能量下进一步进行非弹性散射测量”所强调的那样，康普顿散射在今天仍然是一个主要的悬而未决的问题。有三个特别令人感兴趣的区域：第一，低光子能量和/或小动量转移的区域，其中电子的结合能是台球般的碰撞场景所暗示的能量转移的量级。第二，所有过程的制度，其中电子不能被视为独立的粒子，但关联是必不可少的，第三，分子靶域。我们将在本项目中讨论这三个制度。为此，我们将首次对气相中单个原子和分子的康普顿散射进行符合实验。这些实验将在欧洲同步辐射设施(汉堡的PETRA3，格勒诺布尔的ESRF)进行，在那里，具有足够光子通量的所谓“粉色”光束(即绕过单色仪的光子束)可用于在极小的低截面上进行此类测量。我们将使用申请者团队共同开发的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。从这两个动量矢量出发，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，我们将获得所有光子偏转角和所有能量转移的各自的角发射分布和抛射电子的能谱。在阿瑟·H·康普顿的基本发现95年后，我们的实验将是第一次对自由原子或分子(气相)同时确定散射光子和被踢电子的动量和方向的研究。这将提供有史以来最详细和最完整的康普顿散射图像。因此，除了它们的教科书性质，我们的符合气相实验将允许解决前面提到的三个区域中康普顿散射的公开问题。我们将在低能下进行研究，其中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，其中电子-电子关联是必不可少的，并探索打破旋转对称性过程的分子中的康普顿散射。

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.