We consider ionization of atomic hydrogen with emission of low-energy electrons by proton and antiproton impact in the range of impact velocities $3\mathrm{a}.\mathrm{u}.\mathrm{}<~v_p<~6\mathrm{a}.\mathrm{u}.\mathrm{},$ where the electron capture by protons is already of minor importance but the differences in hydrogen ionization due to proton and antiproton impact can still be substantial. By calculating various differential cross sections within the first and second Born and continuum-distorted-wave–eikonal-initial-state (CDW-EIS) approximations we attempt to analyze the dynamics of hydrogen ionization by protons and antiprotons. We discuss in some detail the role of (i) the interaction between the projectile and the target nucleus and (ii) multiphoton exchanges between the projectile and the target electron. Profound charge-sign effects are suggested by CDW-EIS and second Born calculations for the fully differential emission pattern. Although after the integration over the electron emission angles these effects substantially diminish, they still remain noticeable even in the total ionization cross section suggesting, in particular, that protons are more effective, compared to antiprotons, in producing soft electron emission from hydrogen in the range of collision velocities under consideration.

• Received 4 February 2003

DOI:https://doi.org/10.1103/PhysRevA.67.062703