Nuclear effect on antiproton trapping in liquid 4He

Abstract

It is known that when antiprotons [pbar]'s are implanted into liquid 4He with a low energy of 5.6 MeV, a very small fraction, 3.6% of them, has an extraordinary long lifetime in the order of a few microseconds at the longest [1]. This delayed fraction “q” should reflect the distribution of angular momentum l of [pbar], f(l), with respect to a 4He atom or the annihilation center of each [pbar]. The present concerns are whether f(l) is a statistical distribution or not, how does the interaction potential influence f(l), and how small the q-value is. Taking into account the energy dissipation by means of the measured electronic stopping power and an interaction potential derived by the Molecular-Orbital theory, we simulate the classical trajectories of [pbar]'s implanted into 4He with an energy of 1 MeV. From the f(l) obtained we obtained three conclusions: the statistical distribution contributes 68%; the interaction potential decisively determines the f(l), especially on the profile of nonstatistical distribution; the delayed fraction is evaluated as q = 3%.