Test of $CP$ Symmetry in Hyperon to Neutron Decays

Abstract

The quantum entangled $J/\psi \to {\Sigma }^{+}{\bar{\Sigma }}^{-}$ pairs from $(1.0087\pm 0.0044)\times 10^{10}$ $J/\psi$ events taken by the BESIII detector are used to study the non-leptonic two-body weak decays ${\Sigma }^{+}\to n{\pi }^{+}$ and ${\bar{\Sigma }}^{-}\to \bar{n}{\pi }^{-}$. The $CP$-odd weak decay parameters of the decays ${\Sigma }^{+}\to n{\pi }^{+}$ (${\alpha }_{+}$) and ${\bar{\Sigma }}^{-}\to \bar{n}{\pi }^{-}$ (${\bar{\alpha }}_{-}$) are determined to be $-0.0565\pm 0.0047_{\mathrm{stat}}\pm 0.0022_{\mathrm{syst}}$ and $0.0481\pm 0.0031_{\mathrm{stat}}\pm 0.0019_{\mathrm{syst}}$, respectively. The decay parameter ${\bar{\alpha }}_{-}$ is measured for the first time, and the accuracy of ${\alpha }_{+}$ is improved by a factor of four compared to the previous results. The simultaneously determined decay parameters allow the first precision $CP$ symmetry test for any hyperon decay with a neutron in the final state with the measurement of $A_{CP}=({\alpha }_{+}+{\bar{\alpha }}_{-})/({\alpha }_{+}-{\bar{\alpha }}_{-})=-0.080\pm 0.052_{\mathrm{stat}}\pm 0.028_{\mathrm{syst}}$. Assuming $CP$ conservation, the average decay parameter is determined as $⟨{\alpha }_{+}⟩=({\alpha }_{+}-{\bar{\alpha }}_{-})/2=-0.0506\pm 0.0026_{\mathrm{stat}}\pm 0.0019_{\mathrm{syst}}$, while the ratios ${\alpha }_{+}/{\alpha }_0$ and ${\bar{\alpha }}_{-}/{\bar{\alpha }}_0$ are $-0.0490\pm 0.0032_{\mathrm{stat}}\pm 0.0021_{\mathrm{syst}}$ and $-0.0571\pm 0.0053_{\mathrm{stat}}\pm 0.0032_{\mathrm{syst}}$, where ${\alpha }_0$ and ${\bar{\alpha }}_0$ are the decay parameters of the decays ${\Sigma }^{+}\to p{\pi }^0$ and ${\bar{\Sigma }}^{-}\to \bar{p}{\pi }^0$, respectively.

References in corpus (6)

• Angular momentum conservation in heavy ion collisions at very high energy
• Observation of $CP$ violation in charm decays
• Number of $J/\psi$ events at BESIII
• ${\Sigma }^{+}$ and ${\bar{\Sigma }}^{-}$ polarization in the $J/\psi$ and $\psi (3686)$ decays
• Spin asymmetries and correlations in lambda-pair production through the radiative return method
• Study of CP violation in hyperon decays at Super Charm-Tau Factories with a polarized electron beam

Cited by in corpus (4)

• Stringent test of $CP$ symmetry in ${\Sigma }^{+}$ hyperon decays
• Tests of CP symmetry in entangled hyperon anti-hyperon pairs at BESIII
• ${\Sigma }^{+}\to p{\ell }^{+}{\ell }^{-}$ decays within the standard model and beyond
• Observation of the Electromagnetic Dalitz Transition $h_c\to e^{+}{e}^{-}{\eta }_c$