Time-dependent close-coupling calculations of double ionization of helium by protons and antiprotons

We analyse the role of dynamic electron correlation in double ionization of helium by the impact of high-energy protons and antiprotons using a time-dependent close-coupling (CC) method. We show that, in any practical implementation of the CC method making use of tractable discrete basis sets to describe the multiple degenerate continuum, a basic limitation is that part of the dynamic correlation is inaccessible. Our results also show that dynamic correlation plays a non-negligible role in double ionization of helium below 400 keV, particularly for proton impact. Still, the results fail to reproduce the observed proton/antiproton difference.