Measurements of the pp→pK+Λ reaction at Tp = 2.28 GeV have been carried out at COSY-TOF. In addition to the Λp FSI and N∗ resonance excitation effects a pronounced narrow structure is observed in the Dalitz plot and in its projection on the pΛ-invariant mass. The structure appears at the pp→NK+Σ threshold and is interpreted as ΣN cusp effect. The observed width of 20 MeV/c2 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+Λ channel, but similar to those observed in the pK+Σ0 channel.
@article{arxiv.1206.0426,
title = {On the SigmaN cusp in the pp -> pK+Lambda reaction},
author = {S. Abd El-Samad and E. Borodina and K. -Th. Brinkmann and H. Clement and E. Doroshkevich and R. Dzhygadlo and K. Ehrhardt and A. Erhardt and W. Eyrich and H. Freiesleben and W. Gast and A. Gillitzer and D. Grzonka and C. Hanhart and F. Hauenstein and P. Klja and K. Kilian and M. Krapp and J. Ritman and E. Roderburg and M. Roeder and M. Schulte-Wissermann and W. Schroeder and T. Sfzick and G. J. Wagner and P. Wintz and P. Wuestner},
journal= {arXiv preprint arXiv:1206.0426},
year = {2015}
}