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

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.