Charged kaon--deuteron interactions offer a sensitive probe of the strangeness sector of QCD at low energy, particularly through their scattering parameters. Despite available theoretical predictions, experimental constraints remain absent, particularly for the $\rm K^{ -}d$ system. The first measurement of femtoscopic correlation functions for $\rm K^{ -}d \oplus K^{ +}\overline{ d}$ and $\rm K^{ +}d \oplus K^{ -}\overline{ d}$ particle pairs in Pb--Pb collisions at $\sqrt{ s_{ \rm NN}}=5.02$ TeV recorded by ALICE at the LHC is presented. Correlation functions for both systems are analyzed in three centrality classes and fitted using the Lednick\'y--Lyuboshitz model to extract the source size and strong interaction scattering lengths. The $\rm K^{ -}d$ scattering length is found to be $\Re f_0 = -1.44 \pm 0.15\text{ (stat.)}^{ +0.10}_{ -0.10}$ (syst.) fm and $\Im f_0 = 1.34 \pm 0.33$ (stat.)$^{ +0.21}_{ -0.15}$ (syst.) fm, while for $\rm K^{ +}d$ the value $\Re f_0 = -0.68 \pm 0.16$ (stat.)$^{ +0.09}_{ -0.09}$ (syst.) fm is obtained. These results provide the first constraints on the $\rm K^{ \pm} d$ interaction modeling at low energy, delivering a long-awaited experimental benchmark for testing chiral QCD dynamics.
Categories: nucl-ex hep-ex