TLDR: Lepton mixing was proposed as a possible source of CP violation in the 60s but experimental evidence obtained only now. They only got 3-sigma statistics which is not quite the standard 5-sigma, but more experiments are upcoming. Potentially very important result and consistent with standard model, this is both good (no new physics) and bad (no new physics).
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TLDR: Lepton mixing was proposed as a possible source of CP violation in the 60s but experimental evidence obtained only now. They only got 3-sigma statistics which is not quite the standard 5-sigma, but more experiments are upcoming. Potentially very important result and consistent with standard model, this is both good (no new physics) and bad (no new physics).