On the Measurement of the Electron-Neutrino Correlation in Neutron Beta Decay

I present a new approach to the measurement of a, the electron-neutrino correlation, in neutron beta decay. A precise measurement of a can lead to a precise determination of ratio of the axial vector and vector coupling constants, G(a)/G(v). Coincidences between electrons and protons are detected in a field-expansion spectrometer. The field-expansion spectrometer is designed to make 1/TOF ≈ | p(p)|. TOF and p(p) are the proton time of flight and momentum. Two segmented Si detectors view both electrons and protons in 4π geometry. The time of flight between the electron and proton are accurately measured in a long, ≈ 1 m, drift distance. The electron energy is accurately measured in the Si detectors. The proton momentum and electron energy determine the electron-neutrino opening angle. I have shown that by sorting the data on proton time of flight and electron energy, a can be determined with a statistical relative standard uncertainty of [Formula: see text] , where n is the number of decays observed. The approach has a number of advantages. The acceptance of the spectrometer is 4π for both particles. Thin-dead-layer segmented Si detectors as well as all other components in the apparatus, are commercially available. There are no material apertures to determine the acceptance of the apparatus. The charged particles interact only with electric and magnetic fields before striking the detectors. Coincident detection of electrons and protons reduces backgrounds, and allows the in situ determination of backgrounds. In the analysis, it is not necessary to sort on the relative electron and proton direction and hence electron back scattering does not cause systematic uncertainties. A time of flight spectrum is obtained for each electron energy. Different parts of the spectra have different sensitivities to a. The medium time of flight parts of the spectra that are insensitive to a can be used to verify the accuracy of the electric and magnetic field determinations.