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Register a new userpK+Lambda final state: towards the extraction of the ppK- contribution
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The reaction p(@3.5,GeV)+p -> p+Lambda + K^+ can be studied to search for the existence of kaonic bound states like ppK^- leading to this final state. This effort has been motivated by the assumption that in p+p collisions the Lambda(1405) resonance can act as a doorway to the formation of the kaonic bound states. The status of this analysis within the HADES collaboration, with particular emphasis on the comparison to simulations, is shown in this work and the deviation method utilized by the DISTO collaboration in a similar analysis is discussed. The outcome suggests the employment of a partial wave analysis to disentangle the different contributions to the measured pK^+Lambda final state.
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Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction $p(3.5GeV)+pto pK^{+}Lambda$. This reaction might contain information about the kaonic cluster $ppK^-$ via its decay into $pLambda$. Due to interference effects in our coherent description of the data, a hypothetical $overline{K}NN$ (or, specifically $ppK^-$) cluster signal must not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectra like $pLambda$. 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 $overline{K}NN$ 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 $pK^{+}Lambda$ 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.
The $vec{p}p rightarrow pK^{+}Lambda$ reaction has been measured with the COSY-TOF detector at a beam momentum of $2.7,mathrm{GeV}/c$. The polarized proton beam enables the measurement of the beam analyzing power by the asymmetry of the produced kaon ($A_N^{K}$). This observable allows the $pLambda$ spin triplet scattering length to be extracted for the first time model independently from the final-state interaction in the reaction. The obtained value is $a_{t} = (-2.55 ^{+0.72}_{-1.39} {}_{textrm{stat.}} pm 0.6_{textrm{syst.}} pm 0.3_{textrm{theo.}})mathrm{fm}$. This value is compatible with theoretical predictions and results from model-dependent analyses.
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 $pLambda$-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.
It is argued that final state enhancements in production reactions at large momentum transfers, such as pp -> K^+ Lambda p, are primarily sensitive to the position of a virtual bound state pole in the Lambda p system rather than the Lambda p scattering length and effective range. These arguments are supported by a study of the dispersion relation derived to describe such processes as a function of the cut-off energy. This shows that the position of the virtual bound state is independent of the cut-off energy.
The reaction pp -> K+ + (Lambda p) was measured at Tp=1.953 GeV and Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. The large final state enhancement near the Lambda p threshold can be described using the standard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously the Lambda p invariant mass spectrum and the total cross section data of the free Lambda p scattering.
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