A major neutrino experiment set amidst six nuclear reactors on Daya Bay near Hong Kong has revealed a long-sought result. Having measured very small deficits of electron antineutrinos (νe) at various short distances from the reactors that create them, the international Daya Bay collaboration reports that θ13, last of the three mixing angles that characterize neutrino oscillation, is definitely not zero.1 In fact, it turns out to be big enough for experimenters now to begin investigating the role of neutrinos in creating the manifest matter–antimatter asymmetry of the cosmos.

The survival of so little antimatter from the Big Bang requires that some fundamental interactions violate CP symmetry—invariance under the combined operations of mirror inversion (P) and charge conjugation (C), the replacement of particles by their antiparticles. It’s long been known that the weak interactions of quarks exhibit some CP...

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