Recent results from the T2K experiment

Abstract

T2K is a long-baseline neutrino oscillation experiment based in Japan. It was the first experiment to observe νe appearance in a νμ beam, and has more recently produced the highest precision measurement of the oscillation parameter θ23 and has begun to probe the charge-parity violation phase δ. Using a νμ beam disappearance sample, T2K measures sin2 θ23 = 0.514+0.055-0.056 and Δm232 = (2.51 ± 0.10)×10−3eV2/c4 assuming the normal mass hierarchy, and sin2 θ23 = 0.511±0.055 and Δm213 = (2.48 ± 0.10)×10−3eV2/c4 assuming the inverted mass hierarchy. A joint fit between νμ beam appearance and disappearance samples produces consistent results for sin2 θ23 and Δm232 whilst also excluding at 90% confidence level the regions δ = [0.15,0.83]π for the normal hierarchy and δ = [− 0.08,1.09]π. Using a ν¯μ${\bar \nu _\mu }$ beam disappearance sample, sin2θ¯23=0.45−0.12+0.29${\sin ^2}{\bar \theta _{23}} = 0.45_{ - 0.12}^{ + 0.29}$ and |Δm¯322|=(2.51±0.28)×10−3eV2/c4${\sin ^2}{\bar \theta _{23}} = 0.45_{ - 0.12}^{ + 0.29}$$ and $$\left| {\Delta \bar m_{32}^2} \right| = (2.51 \pm 0.28) \times {10^{ - 3}}\,{\rm{e}}{{\rm{V}}^2}/{{\rm{c}}^4}$, consistent with previous measurements and the T2K νμ sample.