Strongly Enhanced Backward Emission of Electrons in Transfer and Ionization

Extreme Matter Institute EMMI, GSI Helmholtzzentrum fu¨r Schwerionenforschung GmbH,Planckstrase 1, D-64291 Darmstadt, Germany(Received 20 October 2011; published 26 January 2012)We studied three-dimensional angular distributions and longitudinal momentum spectra of electronsejected in transfer plus ionization (TI), i.e., the ejection of one and the capture of a second target electron,for ion-helium collisions. We observe a pronounced structure strongly focused opposite to the projectilebeam direction, which we associate with a new correlated TI mechanism proposed recently. This processcontributessignificantlytothetotalcross sectionsoverabroadrangeofperturbations ,evenat aslargeas 0.5, where uncorrelated TI mechanisms were thought to be dominant.