Precise Measurements of Decay Parameters and $CP$ Asymmetry with Entangled $\Lambda -\bar{\Lambda }$ Pairs

Abstract

Based on 10 billion $J/\psi$ events collected at the BESIII experiment, a search for $CP$ violation in $\Lambda$ decay is performed in the difference between $CP$-odd decay parameters ${\alpha }_{-}$ for $\Lambda \to p{\pi }^{-}$ and ${\alpha }_{+}$ for $\bar{\Lambda }\to \bar{p}{\pi }^{+}$ by using the process $e^{+}{e}^{-}\to J/\psi \to \Lambda \bar{\Lambda }$. With a five-dimensional fit to the full angular distributions of the daughter baryon, the most precise values for the decay parameters are determined to be ${\alpha }_{-}=0.7519\pm 0.0036\pm 0.0024$ and ${\alpha }_{+}=-0.7559\pm 0.0036\pm 0.0030$, respectively. The $\Lambda$ and $\bar{\Lambda }$ averaged value of the decay parameter is extracted to be ${\alpha }_{\mathrm{avg}}=0.7542\pm 0.0010\pm 0.0024$ with unprecedented accuracy. The $CP$ asymmetry $A_{CP}=({\alpha }_{-}+{\alpha }_{+})/({\alpha }_{-}-{\alpha }_{+})$ is determined to be $-0.0025\pm 0.0046\pm 0.0012$, which is one of the most precise measurements in the baryon sector. The reported results for the decay parameter will play an important role in the studies of the polarizations and $CP$ violations for the strange, charmed and beauty baryons.

References in corpus (8)

• Matter and Antimatter in the Universe
• Observation of $CP$ violation in charm decays
• Number of $J/\psi$ events at BESIII
• Weak phases and CP-symmetry tests in sequential decays of entangled double-strange baryons
• Spin asymmetries and correlations in lambda-pair production through the radiative return method
• Bayesian analysis of $b\to s{\mu }^{+}{\mu }^{-}$ Wilson coefficients using the full angular distribution of ${\Lambda }_b\to \Lambda (\to p{\pi }^{-}){\mu }^{+}{\mu }^{-}$ decays
• Direct CP violation in beauty and charm hadron decays
• Charmed baryon decay asymmetry in e+e- annihilation

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