Measurement of the pn → ppπ0π− Reaction in Search of the ABC Resonance
1 Physikalisches Institut, Univ. Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen Germany
2 Kepler Center for Astro and Particle Physics, Univ. Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen Germany
a e-mail: firstname.lastname@example.org
With pd collisions at Tp = 1.2 GeV exclusive measurements of the quasi-free pn → ppπ0π− reaction have been carried out. Using the WASA detector setup at COSY total and differential cross sections have been obtained for the energy region √s = 2.35 − 2.48 GeV. Though this includes the region of the ABC effect and its associated resonance structure, no low-mass enhancement (ABC effect) is found in the π0π−-invariant mass spectrum – in agreement with the constraint from Bose statistics demanding the isovector pion pair to be in relative p-wave. Conventional calculations including t-channel processes for Roper, Δ(1600) and ΔΔ excitations and their decays, which are well-known from the study of the two-pion production in pp collisions, provide a reasonable description of the data at high energies, but fall low at low energies. From this we conclude that a large contribution from a so far unknown isoscalar low-energy process is missed in the calculations. Inclusion of the ABC resonance at m = 2.37 GeV with Γ = 70 MeV and I(JP) = 0(3+), which was recently observed in the pn → dπ0π0 reaction, leads to a much improved description of the data at low energies.
© Owned by the authors, published by EDP Sciences, 2012
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.