Kinematically complete experimental study of Compton scattering at helium atoms near the threshold

Abstract

Compton scattering is one of the fundamental interaction processes of light with matter. When discovered [1], it was described as a billiard-type collision of a photon 'kicking' a quasi-free electron. With decreasing photon energy, the maximum possible momentum transfer becomes so small that the corresponding energy falls below the binding energy of the electron. In this regime, ionization by Compton scattering becomes an intriguing quantum phenomenon. Here, we report on a kinematically complete experiment studying Compton scattering o helium atoms in that regime. We determine the momentum correlations of the electron, the recoiling ion and the scattered photon in a coincidence experiment based on cold target recoil ion momentum spectroscopy, nding that electrons are not only emitted in the direction of the momentum transfer, but that there is a second peak of ejection to the backward direction. This nding links Compton scattering to processes such as ionization by ultrashort optical pulses [2], electron impact ionization [3,4], ion impact ionization [5,6], and neutron scattering [7], where similar momentum patterns occur.

An Overview of the Compton Scattering Calculation

“…By measuring the angular distribution of scattered photons, the experimental observations present large deviations with the FEA results. However, when SM approach is employed and ab initio numerical calculations are carried out, the experimental data are consistent with theoretical predictions [41]. These results indicate that the SM approach is becoming an promising tool to duel with Compton scattering with bound electrons, in which many-body effects have been considered efficiently, and it may have great impacts in this area in the near future.…”

“…Recently, the SM formulation has revealed many nontrivial properties of Compton scattering, and it has attracted lots of interests in interdisciplinary studies [29,32]. Furthermore, there are several experiments which give supporting to the SM predictions [35][36][37][38][39][40][41]. Recently, Max Kircher et al conducted an kinematically complete Compton scattering experiment utilizing X-rays produced from accelerators with energy about 2.1 keV.…”

Observation of Photoion Backward Emission in Photoionization of He and N2

“…In this case, the photon momentum is transferred to the electron and the ion is thus left with a momentum distribution centered at the origin (see Refs. [26,27] for more detailed discussions of the momentum balance for Compton scattering). For the low-energy data we extrapolate the zero as we show in more detail in Fig.…”

Comparative analysis of the Compton ionization of Hydrogen and Positronium

“…In paper [2], the Compton ionization of a hydrogen atom by a high-energy photon of several keV was discussed in detail, and interesting features of various differential cross sections were noted. This paper was inspired by the latest experiments on the Compton ionization of helium atoms using the COLTRIMS detector [3]. A characteristic feature of these experiments is the measurement in coincidence of the momenta of an electron and the residual ion in the range of angles practically equal to 4π, whereas the angle and energy of the scattered photons are calculated from the conservation laws.…”