Speaker
Description
This talk presents the study of strangeness production mechanisms in the $pp \to ppK^{+}K^{-}$ reaction, analyzed using data collected with HADES at GSI and a $4.5\,\mathrm{GeV}$ proton beam. This reaction has been studied over the past two decades at DISTO, COSY-TOF and COSY-11, ANKE, and HADES, revealing rich strangeness production dynamics but leaving a number of questions unresolved, such as the production mechanism and polarization of $\phi(1020)$, the role of $N^*$ resonances, and the nature of the $\Lambda(1405)$ -- a long-debated candidate for a dynamically generated, molecular-like state near the $\bar{K}N$ threshold.
With the purity of the selected event sample reaching $S/B \approx 30$, the reconstructed differential cross sections show clear contributions from the $\phi(1020)\!\to\!K^{+}K^{-}$ and $\Lambda(1520)\!\to\!pK^{-}$ decays. The production of $\phi(1020)$ has been studied in terms of its polarization, as well as in the context of excited baryon decay, with signatures of $N^*(2100)/N^*(2120) \to p\phi(1020)$ contributions.
A noticeable threshold enhancement in the $pK^-$ invariant mass distribution has been observed and interpreted using a $K$-matrix description of the $\Lambda(1405)$, fitted simultaneously with the data of the $\Sigma^0\pi^0$ final state in the same proton-proton collisions. The talk will include the extraction of the $\Lambda(1405)$ pole positions and a systematic comparison with other hypotheses.