Shift and broadening of resonance lines of the antiprotonic helium atoms in liquid He-4

TL;DR

This paper calculates how the resonance lines of antiprotonic helium atoms are shifted and broadened in liquid and superfluid helium-4, showing that these atoms serve as effective probes of helium's properties.

Contribution

The study provides a combined analysis of collective and single-atom interactions affecting resonance lines, using phenomenological and quasistatic models, to understand antiprotonic helium behavior in liquid helium.

Findings

Resonance line shifts and broadenings are quantitatively estimated.

Antiprotonic helium acts as a non-intrusive probe of liquid helium properties.

The models show good agreement with experimental data.

Abstract

The shift and broadening of the resonance lines in spectrum of the antiprotonic helium atoms $\bar{p}\mathrm{He}^{+}$ located in fluid and superfluid $^4$He have been calculated. The contributions to the shift and broadening from collective degrees of freedom in liquid $^4$He have been estimated using the phenomenological response function. Effects due to the interaction of $\bar{p}\mathrm{He}^{+}$ with a single $^4$He atom have been calculated in the quasistatic approximation using the experimental pair correlation function. It has been shown that an implanted $\bar{p}\mathrm{He}^{+}$ atom establishes a good probe of liquid helium properties, since this atom practically does not change the target structure.