On the production of $\pi^{+}_{}$ $\pi^{+}_{}$ pairs in pp collisions at 0.8 GeV

Abstract

Data accumulated recently for the exclusive measurement of the pp $\rightarrow$ pp $\pi^{+}_{}$ $\pi^{-}_{}$ reaction at a beam energy of 0.793GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the pp $\rightarrow$ nn $\pi^{+}_{}$ $\pi^{+}_{}$ reaction channel. The latter is expected to be the only $\pi$ $\pi$ production channel, which contains no major contributions from resonance excitation close to threshold and hence should be a good testing ground for chiral dynamics in the $\pi$ $\pi$ production process. No single event has been found, which meets all conditions for being a candidate for the pp $\rightarrow$ nn $\pi^{+}_{}$ $\pi^{+}_{}$ reaction. This gives an upper limit for the cross-section of 0.16μb (90% C.L.), which is more than an order of magnitude smaller than the cross-sections of the other two-pion production channels at the same incident energy.