ISSN - 03702693, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 2009, vol. 679, p. 30-35
Two-pion production in proton-proton collisions - experimental total cross sections and their isospin decomposition
The two-pion production in pp-collisions has been investigated at CELSIUS in exclusive measurements from threshold up to Tp = 1.36 GeV. Total and differential cross sections have been obtained for the channels p n π+ π0, p p π+ π-, p p π0 π0 and also n n π+ π+. For intermediate incident energies Tp > 1 GeV, i.e. in the region which is beyond the Roper excitation but at the onset of ΔΔ excitation, the total p p π0 π0 cross section falls behind theoretical predictions by as much as an order of magnitude near 1.2 GeV, whereas the n n π+ π+ cross section is a factor of five larger than predicted. An isospin decomposition of the total cross sections exhibits a s-channel-like energy dependence in the region of the Roper excitation as well as a significant contribution of an isospin 3/2 resonance other than the Δ (1232). As possible candidates the Δ (1600) and the Δ (1700) are discussed. © 2009 Elsevier B.V. All rights reserved.