Determination of the electron–antineutrino angular correlation coefficient a0 and the parameter |?| = |GA/GV | in free neutron ß-decay from measurements of the integrated energy spectrum of recoil protons stored in an ion trap

Recoil protons from the ß-decay of unpolarized neutrons are stored in a cryogenic ion trap formed by the superposition of an axisymmetric electrostatic field on a coaxial magnetic field, which varies uniformly in space between regions of high (~4.30 T) and low (~0.61 T) homogeneous field. Protons generated in the high field region are adiabatically focused onto a 'mirror' electrode in the low field region. The integrated energy spectrum is determined by counting the number of stored protons as a function of mirror potential. Violation of the exact adiabatic conditions is corrected for by carrying out alternate measurements at trapping times which differ by a factor of 2. The results: a0 = -0.1054 ± 0.0055, |?| = 1.271 ± 0.018 are in agreement with previous measurements of these quantities.