On the Production of $\ddot{I}{€}^{+}\ddot{I}{€}^{+}$ Pairs in pp Collisions at 0.8 GeV

Abstract

Data accumulated recently for the exclusive measurement of the $pp\to pp\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ reaction at a beam energy of 0.793 GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the $pp\to nn\ddot{I}{€}^{+}\ddot{I}{€}^{+}$ reaction channel. The latter is expected to be the only $\ddot{I}€\ddot{I}€$ 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 $\ddot{I}€\ddot{I}€$ production process. No single event has been found, which meets all conditions for being a candidate for the $pp\to nn\ddot{I}{€}^{+}\ddot{I}{€}^{+}$ reaction. This gives an upper limit for the cross section of 0.16 $\hat{I}¼$b (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.