Study of the reaction π−p→N 33 *++ π−− and ππ elastic scatteringand ππ elastic scattering

Approximately 3500 four-prong events, observed in the Saclay 81 cm LHBC exposed at the CERN PS to a beam of 2.75 GeV/c π− mesons, have been analysed; the cross-sections for the different multipion channels have been determined. 1324 events correspond to the reaction π−+p→π−+p+π−+π+ which is characterized by an important production of theN 33 *++ isobar (σ=0.61 mb) and of the ρ0 resonance (σ=0.36 mb). TheN 33 *++ isobar appears to be mainly produced according to an OPE mechanism. The σππ elastic cross-section in a pureT=2 state is evaluated as a function of the dipion energy; scattering angular distributions for different (π−π−) mass intervals are also analysed.