A measurement of the antineutrino asymmetry B in free neutron decay

We have measured the antineutrino asymmetry B in neutron beta decay, i.e., the correlation of the neutron spin and the antineutrino momentum, with a new method. Our result is B=0.967±0.006stat±0.010syst=0.967±0.012. Statistical and systematic uncertainty can be considerably reduced in future experiments.