Title: State-selective influence of the Breit interaction on the angular distribution of emitted photons following dielectronic recombination,
Abstract: We report a measurement of $KLL$ dielectronic recombination in charge states
from Kr$^{+34}$ through Kr$^{+28}$, in order to investigate the contribution of
Breit interaction for a wide range of resonant states. Highly charged Kr ions
were produced in an electron beam ion trap, while the electron-ion collision
energy was scanned over a range of dielectronic recombination resonances. The
subsequent $K\alpha$ x rays were recorded both along and perpendicular to the
electron beam axis, which allowed the observation of the influence of Breit
interaction on the angular distribution of the x rays. Experimental results are
in good agreement with distorted-wave calculations. We demonstrate, both
theoretically and experimentally, that there is a strong state-selective
influence of the Breit interaction that can be traced back to the angular and
radial properties of the wavefunctions in the dielectronic capture.