Abashian-Booth-Crowe resonance structure in the double pionic fusion to 4He

Abstract

Exclusive and kinematically complete high-statistics measurements of the double pionic fusion reaction dd→4Heπ0π0 have been performed in the energy range 0.8-1.4 GeV covering thus the region of the Abashian-Booth-Crowe effect, which denotes a pronounced low-mass enhancement in the ππ invariant mass spectrum. The experiments were carried out with the WASA detector setup at the cooler synchrotron at Forshungszentrum Julich GmbH. Similar to the observation in the basic pn→dπ0π0 reaction, the data reveal a correlation between the ABC effect and a resonancelike energy dependence in the total cross section. The maximum occurs at m=2.37 GeV + 2mN, i.e., at the same position as in the basic reaction. The observed resonance width Γ160 MeV can be understood from broadening due to Fermi motion of the nucleons in initial and final nuclei together with collision damping. Differential cross sections are described equally well by the hypothesis of a pn resonance formation during the reaction process. © 2012 American Physical Society.