The reaction Li-7(pi(+),pi(-))B-7 and its implications for B-7

The reaction Li-7(pi(+),pi(-))B-7 has been measured at incident pion energi es of 30-90 MeV. Li-7 constitutes the lightest target nucleus, where the pi onic charge exchange may proceed as a binary reaction to a discrete final s tate. Like in the Delta-resonance region the observed cross sections are mu ch smaller than expected from the systematics found for heavier nuclei. In analogy to the neutron halo case of Li-11 this cross section suppression is interpreted as evidence for a proton halo in the particle-unstable nucleus B-7. (C) 1998 Elsevier Science B.V. All rights reserved.