Measurement of the weak neutral current excitation at Eνμ=29.8 MeV

Abstract The weak neutral current reaction 12 C( ν μ , ν μ ′ ) 12 C ∗ (1 + ,1; 15.1MeV) has been observed for the first time in the KARMEN experiment. Neutrino events were separated from background using two different analysis methods. The measured cross section σ NC =(3.2 ± 0.5 stat. ± 0.4 syst. ) × 10 −42 cm 2 for monoenergetic ν μ from π + -decay at rest is in good agreement with the standard model, the isovector-axialvector coupling constant of weak hadronic current deduced from this experiment is | β |=1.11±0.13.