Cross sections of negative-pion-induced reactions in 9Be, 12C and 19F nuclei between 0.4 and 1.9 GeV

Abstract

Abstract Cross sections of negative-pion-induced reactions in 9Be, 12C and 19F have been measured at energies between 0.4 and 1.9 GeV by detecting the induced radioactivity. The excitation function of the 9Be(π−, πN)8Li reaction and those of the 12C(π−, π−n)11C and 19F(π−, π−n)18F reactions exhibit T = 1 2 resonances at Eπ = 0.6 and 0.9 GeV and a T = 3 2 resonance at 1.3 GeV. The resonance peaks are broadened apparently by the Fermi motion of the struck nucleon in the nucleus. The cross-section ratio σ( 9 Be (π − , π N ) 8 Li / σ π − p , where σπ−p is the free particle over the Fermi momentum, decreases rather monotonically like that for the (p, pn) reaction with increasing incident energy, while the ratios of σ(π − , π − n) σ π − n for the 12C(π−), π−n11C and 19F(π−, π−n)18F reactions are enhanced around Eπ = 0.6 GeV. This enhancement is explained partly by the charge exchange of the nucleon emitted from the Δ-particle formed through the decay of the T = 1 2 isobar. However, another mechanism should be needed to understand the enhancement of the (π−, π−n) reaction cross section around 0.6 GeV. The excitation functions for the 9 Be 6 He , 12 C ( 8 B , 8 Li ) and 12 C 6 He reactions indicate that the initial pion-nucleon.