Recent results from the T2K experiment

Lancaster University, Bailrigg, Lancaster, United Kingdom, LA1 4YW

^* e-mail: m.lawe@lancaster.ac.uk

Published online: 28 October 2016

Abstract

T2K is a long-baseline neutrino oscillation experiment based in Japan. It was the first experiment to observe ν_e appearance in a ν_μ 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 ν_μ 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 ν_μ 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 $${\overline{\nu }}_{\mu }$$ beam disappearance sample, $${\sin }^2{\overline{\theta }}_{23}={0.45}_{-0.12}^{+0.29}$$ and $$\left|\Delta {\overline{m}}_{32}^2\right|=\left(2.51\pm 0.28\right)\times {10}^{-3}e{V}^2/c^4$$, consistent with previous measurements and the T2K ν_μ sample.