On the SigmaN cusp in the pp -> pK+Lambda reaction
  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 projection on the $p\Lambda$-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. 
S. Abd El-Samad, E. Borodina, K.-Th. Brinkmann, H. Clement, E.   Doroshkevich, R. Dzhygadlo, K. Ehrhardt, A. Erhardt, W. Eyr...
nucl-ex hep-ex