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Title: Do neutrino oscillations violate CP symmetry?
Plain: If neutrinos and antineutrinos oscillate differently, leptons break the matter-antimatter mirror symmetry called CP. This may link to why the universe contains matter.
Precise: Measure the PMNS phase $\delta_{\mathrm{CP}}$ and determine whether $\operatorname{sin}(\delta_{\mathrm{CP}}) \ne 0$ at $\ge 5\sigma$ using $\nu_{\mu} \to \nu_e$ versus anti-nu_mu -> anti-nu_e appearance. Answer: $\delta_{\mathrm{CP}}$ with uncertainty $\sim 10\text{ to }20\ \mathrm{deg}$ and the yes-no CP verdict.
Settled by: DUNE and Hyper-Kamiokande appearance data over about 10 years, after the mass ordering is fixed.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: open
Status note: The 2025 NOvA plus T2K joint analysis (Nature) excludes CP conservation at about $3\sigma$ only if the ordering is inverted; for normal ordering CP conservation remains allowed.
Posed since: (empty)