Subthreshold pi0 production in the reactions Mg-24 (alpha, pi0) X at 43-MeV/A and Mg-24 (O-16, pi0) X at 24-MeV/A and 33-MeV/A

Waters, M. ; Machner, H. ; Gotta, D. ; et al.
Nucl.Phys.A 564 (1993) 595-608, 1993.
Inspire Record 365059 DOI 10.17182/hepdata.16594

The subthreshold production of neutral pions was studied in the reactions 24 Mg(α,π 0 )X at 43 MeV·. A and 24 Mg( 16 O,π 0 )X at 24 and 33 MeV·. A . The energies and emission angles of the two coincident photons from the π 0 -decay were measured with a lead glass shower detector. The cross sections of 3.5 and 6.6 nb from the 16 O-induced reactions are compatible with other experiments in this energy region. For the α-induced reaction a production cross section of 1.3 nb was found. Here, only 22 MeV above the absolute threshold, the pion emission from an excited Δ -nucleon hole state is strongly suppressed. The differential cross sections at very backward angles are by an order of magnitude bigger than the yields at 90° pointing to a strong absorption of the produced pions by the larger target nucleus.

1 data table

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