# Ab initio QED treatment of the two-photon annihilation of positrons with bound electrons

## TL;DR

This paper develops a fully relativistic ab initio QED framework to accurately describe positron-bound electron annihilation with two-photon emission, resolving previous theoretical-experimental discrepancies for silver atoms.

## Contribution

It introduces a novel ab initio QED approach for positron-electron annihilation, improving accuracy over previous approximations and resolving longstanding disagreements.

## Key findings

- Resolved the discrepancy between theory and experiment for silver atoms.
- Demonstrated significant differences from previous approximation methods.
- Provided a more accurate relativistic description of the annihilation process.

## Abstract

The process of a positron $\unicode{x2013}$ bound-electron annihilation with simultaneous emission of two photons is investigated theoretically. A fully relativistic formalism based on $\textit{ab initio}$ QED description of the process is worked out. The developed approach is applied to evaluate the annihilation of a positron with $K$-shell electrons of a silver atom, for which a strong contradiction between theory and experiment was previously stated. The results obtained here resolve this long-standing disagreement and, moreover, demonstrate a sizeable difference with approaches so far used for calculations of the positron $\unicode{x2013}$ bound-electron annihilation process, namely, the $\textit{Lee's}$ and $\textit{impulse}$ approximations.