On the SigmaN cusp in the pp -> pK+Lambda reaction

Abstract

Measurements of the $pp\to p{K}^{+}\hat{I}›$ reaction at $T_p$ = 2.28 GeV have been carried out at COSY-TOF. In addition to the $\hat{I}›p$ FSI and $N^{\ast }$ resonance excitation effects a pronounced narrow structure is observed in the Dalitz plot and in its projection on the $p\hat{I}›$-invariant mass. The structure appears at the $pp\to$N$K^{+}\hat{I}\pounds$ threshold and is interpreted as $\hat{I}\pounds$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 $p{K}^{+}\hat{I}›$ channel, but similar to those observed in the $p{K}^{+}\hat{I}{\pounds }^0$ channel.