THE ELECTRON–ANTINEUTRINO ANGULAR CORRELATION IN FREE NEUTRON DECAY

Free neutron beta decay is the simplest nuclear beta decay and the prototype charged-current semileptonic decay. It has some theoretical advantage over other nuclear decay systems in that there are no nuclear structure corrections, and it is the only mixed Fermi/Gamow–Teller beta decay for which the relative matrix elements can be directly calculated. The status of the electron–antineutrino angular correlation (a-coefficient) in neutron beta decay and its role in elucidating fundamental properties of the weak interaction are reviewed, with an emphasis on experiments. A new generation of experiments intended to reduce the uncertainty in the a-coefficient to less than 1% is described.