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

TL;DR

This study reports the observation of a narrow Sigma-N cusp in the $pp o pK^+\Lambda$ reaction at COSY-TOF, revealing a broader width than previously expected and providing insights into hyperon-nucleon interactions.

Contribution

First observation of a Sigma-N cusp in the $pp o pK^+\Lambda$ reaction, with detailed analysis of its width and angular distributions, advancing understanding of hyperon-nucleon dynamics.

Findings

Narrow Sigma-N cusp observed at threshold.

Cusp width measured at 20 MeV/$c^2$, broader than prior measurements.

Angular distributions suggest similarities to the $pK^+\Sigma^0$ channel.

Abstract

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.