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

Abstract

We present a precision measurement of the axial-vector coupling constant $g_A$ 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 $\hat{I}»=g_A/g_V=-1.27641(45{)}_{\mathrm{stat}}(33{)}_{\mathrm{sys}}$ which confirms recent measurements with improved precision. This corresponds to a value of the parity violating beta asymmetry parameter of $A_0=-0.11985(17{)}_{\mathrm{stat}}(12{)}_{\mathrm{sys}}$. We discuss implications on the CKM matrix element $V_{ud}$ and derive a limit on left-handed tensor interaction.