Collisional Stark Transitions and Induced Annihilation of Cold Antiprotonic Helium Ions

TL;DR

This study investigates how low-energy collisions between antiprotonic helium ions and helium atoms cause Stark transitions and annihilation, revealing the dominant role of long-range polarization interactions and aligning with recent experimental data.

Contribution

It presents a quantum coupled-channels analysis of collisional processes in antiprotonic helium ions, including all relevant states and interactions, providing new insights into annihilation cross sections and transition rates.

Findings

Long-range polarization interactions dominate the processes.

Effective annihilation cross sections are induced for initial l up to 15.

Calculated transition rates agree with recent experimental data.

Abstract

Stark transitions and induced annihilation of antiproton in the collisions of antiprotonic helium ions (\bar{p}He^{+2})_{nl} with He atoms at very low energy (~ 10 K) are considered in the framework of quantum coupled-channels method taking into account all the states with different l at given n~30, including the annihilating ns and np-states. Elastic scattering, Stark transitions and induced annihilation during collisions are produced by scalar and dipole terms in the interaction. It is shown that the most important contribution to the processes comes from the long-range polarization interaction. Admixtures of the ns and np-states to the states with higher l during collisions induce the effective annihilation cross sections for the initial l up to 15, but don't affect the Stark cross sections for the initial states nearly to circular orbits. Total rates of the Stark transitions from the circular orbits with n=28 - 32, averaged over the thermal motion, are compatible with the recent ASACUSA data. Isotope effect as well as the dependence on n are also qualitatively agree with the experiment.