Processes with three or more charged particles in the final state exhibit a particular threshold behavior, as inferred by the famous Wannier law for a ($2e+$ion) system. We formulate a general solution which determines the threshold behavior of the cross section for multiple fragmentation. Applications to several systems of particular importance with three, four, and five leptons (electrons and positrons) in the field of a charged core, and two pairs of identical particles with opposite charges, are presented. Threshold exponents for these systems are predicted, while some previously suggested threshold laws are revised.

• Received 16 December 1997

DOI:https://doi.org/10.1103/PhysRevA.58.321