Partial Wave Analysis of the Reaction $p(3.5GeV)+p\to p{K}^{+}\mathrm{\Lambda }$ to Search for the "$pp{K}^{-}$" Bound State

Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction $p(3.5GeV)+p\to p{K}^{+}\mathrm{\Lambda }$. This reaction might contain information about the kaonic cluster “$pp{K}^{-}$” via its decay into $p\mathrm{\Lambda }$. Due to interference effects in our coherent description of the data, a hypothetical $\bar{K}NN$ (or, specifically “$pp{K}^{-}$”) cluster signal must not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectra like $p\mathrm{\Lambda }$. Our PWA analysis includes a variety of resonant and non-resonant intermediate states and delivers a good description of our data (various angular distributions and two-hadron invariant mass spectra) without a contribution of a $\bar{K}NN$ cluster. At a confidence level of CL${}_s$=95% such a cluster can not contribute more than 2-12% to the total cross section with a $p{K}^{+}\mathrm{\Lambda }$ final state, which translates into a production cross-section between 0.7 $\mu b$ and 4.2 $\mu b$, respectively. The range of the upper limit depends on the assumed cluster mass, width and production process.