Precision tests of Quantum Mechanics and CPT symmetry with entangled neutral kaons at KLOE

Abstract

The quantum interference between the decays of entangled neutral kaons is a very powerful tool for testing the quantum coherence of the entangled kaon pair state. The studied process $\phi\rightarrow K_SK_L\rightarrow\pi^+\pi^-\pi^+\pi^-$ exhibits the characteristic Einstein-Podolsky-Rosen correlations that prevent both kaons to decay into $\pi^+\pi^-$ at the same time. The newly published result is based on data sample collected with the KLOE detector at DA$\Phi$NE and corresponds to an integrated luminosity of about 1.7 fb$^{-1}$ , i.e. to $\sim$ 1.7 $\times$ 10$^9$ $\phi\rightarrow K_SK_L$ decays. From the fit to the observed time difference distribution of the two kaon decays, the decoherence and CPT violation parameters of various phenomenological models are measured. A stringent upper limit on the branching ratio of the $\phi \rightarrow K_S K_S , K_L K_L$ decay is also derived. Independently, the comparison of neutral meson transition rates between flavour and CP eigenstates allows direct and model independent tests of time-reversal T and CPT symmetries to be conducted, through ratios of rates of two classes of processes: $K_S K_L \to (\pi^{\pm}e^{\mp}\nu)(3\pi^0)$ and $K_S K_L \to (\pi^{+}\pi^{-})(\pi^{\pm}e^{\mp}\nu)$. In addition to this a straightforward extension to the case of CPT symmetry is performed providing the first model independent test of CPT symmetry violation in transitions of neutral kaons.