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First Measurement of the Decay Asymmetry in the Pure $W$-Boson-Exchange Decay ${\Lambda }_{c}^{+}\to {\Xi }^{0}{K}^{+}$

2024    CERN İşbirliği

Based on $4.4\text{}\text{}{\mathrm{fb}}^{-1}$ of ${e}^{+}{e}^{-}$ annihilation data collected at the center-of-mass energies between 4.60 and 4.70 GeV with the BESIII detector at the BEPCII collider, the pure $W$-boson-exchange decay ${\Lambda }_{c}^{+}\to {\Xi }^{0}{K}^{+}$ is studied with a full angular analysis. The corresponding decay asymmetry is measured for the first time to be ${\alpha }_{{\Xi }^{0}{K}^{+}}=0.01±0.16\left(\mathrm{stat}\right)±0.03\left(\mathrm{syst}\right)$. This result reflects the noninterference effect between the $S$- and $P$-wave amplitudes. The phase shift between $S$- and $P$-wave amplitudes has two solutions, which are ${\delta }_{p}-{\delta }_{s}=-1.55±0.25\left(\mathrm{stat}\right)±0.05\left(\mathrm{syst}\right)\text{}\text{}\mathrm{rad}$ or $1.59±0.25\left(\mathrm{stat}\right)±0.05\left(\mathrm{syst}\right)\text{}\text{}\mathrm{rad}$.