Measurement of the Weak Axial-Vector Coupling Constant in the Decay of Free Neutrons Using a Pulsed Cold Neutron Beam

We present a precision measurement of the axial-vector coupling constant gA in the decay of polarized free neutrons. For the first time, a pulsed cold neutron beam was used for this purpose. By this method, leading sources of systematic uncertainty are suppressed. From the electron spectra we obtain λ=gA/gV=-1.27641(45)ₛₜₐₜ(33)sys, which confirms recent measurements with improved precision. This corresponds to a value of the parity violating beta asymmetry parameter of A₀=-0.11985(17)ₛₜₐₜ(12)sys. We discuss implications on the Cabibbo-Kobayashi-Maskawa matrix element Vud and derive a limit on left-handed tensor interaction.