On the ΣN cusp in the pp → pK+Λ reaction

Abstract

Abstract. 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 strongly asymmetric structure appears at the pp → N K + Σ threshold and is interpreted as ΣN cusp effect. The observed width of about 20 MeV/c 2 is substantially broader than anticipated from previous measurements as well as theoretical predictions. 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 + Σ 0 channel.

Determination of N* amplitudes from associated strangeness production in p+p collisions

“…The resulting p-Λ system then may appear in an S-wave state in case of J P = 0 + or in an s-or d-wave state in case of J P = 1 + . This has also been confirmed by an analysis of the Σ-N cusp carried out by the COSY-TOF collaboration [38]. Additionally, since the cusp is a resonance structure in analogy to the N * , the Breit-Wigner parametrization is used for A 2b (Eq.…”

“…This coherent approach differs from the analysis techniques usually employed for the extraction of scattering parameters [37] and should be considered as complementary. Another intermediate channel contributing to pK + Λ final state is the Σ-N cusp, which appears at or above the Σ-N threshold (2130 MeV/c 2 ) [38]. The coupling between the Σ-N and Λ-N channels leads to an enhancement of the cross-section in the p-Λ final state in a mass range close to the above mentioned threshold.…”

Application of Straw Tube Detectors to Hyperon Studies

“…This high resolution of the pΛ invariant mass is mainly due to the performance of the high resolution straw tube tracker in the COSY-TOF detector which improved the mass resolution by a factor of ≈3 compared to the previous setup of the COSY-TOF detector without the STT [5]. The Dalitz plot distribution shows that the COSY-TOF detector covers the complete kinematically allowed region of the pp → pK + Λ reaction.…”

Reanalysis ofp+preaction data: Probable absence of appK−state

“…Three issues were mainly investigated thereby: the production of N * resonances and their subsequent decay into K + Λ [2][3][4][5][6][7][8][9][10], the pΛ final state interaction [7,[11][12][13], and the cusp structure appearing at 2.13 GeV in the pΛ invariant mass distribution [14][15][16]. A fourth aspect was recently added to this list with the investigation of the kaonic nuclear bound state KN N by the DISTO collaboration [17,18].…”

“…The upper row shows measurements from the COSY-TOF Collaboration at two different beam kinetic energies [16]. The data are compared to phase space simulations indicated in yellow.…”