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 studied in the process ϕ → K_SK_L → π⁺π⁻π⁺π⁻, which exhibits the characteristic Einstein-Podolsky-Rosen correlations that prevent both kaons to decay into π⁺π⁻ at the same time. This constitutes a very powerful tool for testing at the utmost precision the quantum coherence of the entangled kaon pair state, and to search for tiny decoherence and $\mathcal{CPT}$ violation effects, which may be justified in a quantum gravity framework.

The analysed data sample was collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory, and corresponds to an integrated luminosity of about 1.7 fb⁻¹, i.e. to about 1.7 × 10⁹ϕ → K_SK_L decays produced. From the fit of the observed ∆t distribution, being ∆t the difference of the kaon decay times, the decoherence and $\mathcal{CPT}$ violation parameters of various phenomenological models are measured with a largely improved accuracy with respect to previous analyses.

The results are consistent with no deviation from quantum mechanics and $\mathcal{CPT}$ symmetry, while for some parameters the precision reaches the interesting level at which — in the most optimistic scenarios — quantum gravity effects might show up. They provide the most stringent limits up to date on the considered models.