Measurement of the pn→ppπ0π- reaction in search for the recently observed resonance structure in dπ0π0 and dπ+π- systems

Abstract

Exclusive measurements of the quasifree pn→ppπ0π- reaction have been performed by means of pd collisions at Tp = 1.2 GeV using the wide angle shower apparatus (WASA) detector setup at the cooler synchrotron COSY (Institut für Kernphysik, Jülich). Total and differential cross sections have been obtained covering the energy region √s = (2.35-2.46) GeV, which includes the region of the ABC effect and its associated resonance structure. No ABC effect, i.e., low-mass enhancement is found in the π0π--invariant mass spectrum, in agreement with the constraint from Bose statistics that the isovector pion pair can not be in relative s wave. At the upper end of the covered energy region t-channel processes for Roper, Δ(1600) and ΔΔ excitations provide a reasonable description of the data, but at low energies the measured cross sections are much larger than predicted by such processes. Adding a resonance amplitude for the resonance at m = 2.37 GeV with Γ = 70 MeV and I(JP)=0(3+) observed recently in pn→dπ0π0 and pn→dπ+π- reactions leads to an agreement with the data also at low energies. © 2013 American Physical Society.