Experimental study of anti π double charge exchange with 7Li

150 double charge exchange events π-+7Li → π++ anything at an incident π- labb kinetic energy of 102 MeV have been observed. The π+ were recorded in an emulsion stack at 30 deg to the incident π- beam. No significant peak due to the hypothetical reaction π-+7Li → π++7H was observed in the part of the π+ energy spectrum corresponding to a 7H binding energy between -5 MeV and +25 MeV. The new upper limit for the corresponding differential cross section is 1.0x10-31 cm2/ster (90% C.L.). The spectrum was recorded down to low energies (20 MeV < Esub(πsup(+)) < 100 MeV); its shape implies a strong final state interaction among the π+, the proton and the six neUtrons. The differential double charge exchange cross section integrated over all π+ energies was determined as (dσ/dΩ)sub(tot) = (4.2+-1.7)x10sup(-30) cm2/ster. ver all π+ energies was determined as (dσ/dΩ)sub(tot) = (4.2+-1.7)x10sup(-30) cm