First Model-Independent Measurement of the Spin Triplet $p\Lambda$   Scattering Length from Final State Interaction in the $\vec{p}p \rightarrow   pK^{+}\Lambda$ Reaction
  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 $p\Lambda$ 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. 
COSY-TOF Collaboration: F. Hauenstein, E. Borodina, H. Clement, E.   Doroshkevich, R. Dzhygadlo, K. Ehrhardt, W. Eyrich, W. ...
nucl-ex