Observation of Anomalously Low Momentum Transfer in the Low Energy Scattering of Large 4He Droplets From 4He and 3He Atoms

The momentum transferred to large superfluid4He droplets\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$(\overline N \approx 1.5 \cdot 10^9 )$$ \end{document}in low energy (≈ 4–10 K) scattering from4He and3He atoms was determined from time of flight measurements after the droplets have passed through a low temperature (T = 1.7–4.2 K) scattering box filled with the gas of either He isotope. The results are compared with3He droplets scattered from either4He or3He gas for which all of the incident momentum is transferred, as expected for classical capture of the scattering gas atoms. In the case of the4He droplets a smaller momentum transfer is found amounting to 65% for4He atoms and 45% for3He atoms but only at the lowest collision energies. These results are consistent with transmission of some of the atoms through the droplets.