title: Projectile-charge sign dependence of four-particle dynamics in helium double ionization.
abstract: Double ionization of helium by 6 MeV proton impact has been explored in a kinematically complete experiment using a "reaction microscope." For the first time, fully differential cross sections for positively charged projectiles have been obtained and compared with data from 2 keV electron impact. The significant differences observed in the angular distribution of the ejected electrons are attributed to the charge sign of the projectile, resulting in different dynamics of the four-particle Coulomb system, which is not considered in the first Born approximation.
authors.affiliation: Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Fischer
authors.forename: R
authors.initials: R
authors.lastname: Moshammer
authors.forename: A
authors.initials: A
authors.lastname: Dorn
authors.forename: J R
authors.initials: JR
authors.lastname: Crespo López-Urrutia
authors.forename: B
authors.initials: B
authors.lastname: Feuerstein
authors.forename: C
authors.initials: C
authors.lastname: Höhr
authors.forename: C D
authors.initials: CD
authors.lastname: Schröter
authors.forename: S
authors.initials: S
authors.lastname: Hagmann
authors.forename: H
authors.initials: H
authors.lastname: Kollmus
authors.forename: R
authors.initials: R
authors.lastname: Mann
authors.forename: B
authors.initials: B
authors.lastname: Bapat
authors.forename: J
authors.initials: J
authors.lastname: Ullrich