Thursday, January 5, 2017

There Is Non-Zero CP Violation In Neutrino Oscillations

While unsurprising, this is perhaps the most definitive evidence that neutrino oscillation governed by the PMNS matrix has a non-zero CP violating phase. Thus, there are differences between the way that neutrinos and anti-neutrinos oscillate.
T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beam. The data include all runs from Jan 2010 to May 2016 and comprise 
7.482×1020,protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135 μ-like events, and 7.471×1020,protons on target in antineutrino mode which yielded 4 e-like and 66 μ-like events. Reactor measurements of sin22θ13 have been used as an additional constraint. The one-dimensional confidence interval at 90% for δCP spans the range (3.130.39) for normal mass ordering. The CP conservation hypothesis (δCP=0,π) is excluded at 90% C.L.
T2K Collaboration, "First combined analysis of neutrino and antineutrino oscillations at T2K" (January 2, 2017).

The study is also notable for how much of a needle in a haystack enterprise neutrino physics is with an immense number of protons on target in neutrino or anti-neutrino mode (10^21) producing just 237 measurable events.



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