Measurements of the $pp to pK^+Lambda$ reaction at $T_p$ = 2.28 GeV have been carried out at COSY-TOF. In addition to the $Lambda p$ FSI and $N^*$ resonance excitation effects a pronounced narrow structure is observed in the Dalitz plot and in its pr
ojection on the $pLambda$-invariant mass. The structure appears at the $pp to $N$K^+Sigma$ threshold and is interpreted as $Sigma$N cusp effect. The observed width of 20 MeV/$c^2$ is substantially broader than anticipated from previous inclusive measurements. Angular distributions of this cusp structure are shown to be dissimilar to those in the residual $pK^+Lambda$ channel, but similar to those observed in the $pK^+Sigma^0$ channel.
Data accumulated recently for the exclusive measurement of the $ppto pppi^+pi^-$ reaction at a beam energy of 0.793 GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the $pp to nnpi^+pi^+$ reaction channel. T
he latter is expected to be the only $pipi$ 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 $pipi$ production process. No single event has been found, which meets all conditions for being a candidate for the $pp to nn pi^+pi^+$ reaction. This gives an upper limit for the cross section of 0.16 $mu$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.
The single-pion production reactions $ppto dpi^+$, $ppto nppi^+$ and $ppto pppi^0$ were measured at a beam momentum of 0.95 GeV/c ($T_p approx$ 400 MeV) using the short version of the COSY-TOF spectrometer. The central calorimeter provided particle i
dentification, energy determination and neutron detection in addition to time-of-flight and angle measurements from other detector parts. Thus all pion production channels were recorded with 1-4 overconstraints. Main emphasis is put on the presentation and discussion of the $nppi^+$ channel, since the results on the other channels have already been published previously. The total and differential cross sections obtained are compared to theoretical calculations. In contrast to the $pppi^0$ channel we find in the $nppi^+$ channel a strong influence of the $Delta$ excitation already at this energy close to threshold. In particular we find a $(3 cos^2Theta + 1)$ dependence in the pion angular distribution, typical for a pure s-channel $Delta$ excitation and identical to that observed in the $dpi^+$ channel. Since the latter is understood by a s-channel resonance in the $^1D_2$ $pn$ partial wave, we discuss an analogous scenario for the $pnpi^+$ channel.
The two-pion production reaction $vec{p}pto pppi^+pi^-$ was measured with a polarized proton beam at $T_p approx$ 750 and 800 MeV using the short version of the COSY-TOF spectrometer. The implementation of a delayed pulse technique for Quirl and cent
ral calorimeter provided positive $pi^+$ identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle measurements. Thus all four-momenta of the emerging particles could be determined with 1-4 overconstraints. Total and differential cross sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous data and theoretical calculations. In contrast to predictions we find significant analyzing power values up to $A_y$ = 0.3.
