Positron scattering on molecular hydrogen: Analysis of experimental and theoretical uncertainties

Abstract

Experiments performed in recent years on positron scattering from molecular hydrogen indicated a rise of the total cross section in the limit of zero energy, but essentially disagree on the amplitude of this rise. Mitroy and collaborators [J.-Y. Zhang et al., Phys. Rev. Lett. 103, 223202 (2009)] predicted a scattering length somewhat different from values deduced experimentally. Using a Markov chain Monte Carlo modified effective range theory (MCMC-MERT) we show that the prediction of Mitroy and collaborators allows one to validate the recent experimental results and determine possible uncertainties. By comparing the MERT analysis with the fixed-nuclei density functional calculations we also deduce that probably the effect of virtual positronium formation (or coupling to the virtual positronium state) determines an almost constant value of the total cross section from 3 eV up to the positronium-formation threshold.