New measurements of the electron-neutron spin asymmetry in neutron beta-decay

Measurement of the neutronβ-asymmetry parameterA0with ultracold neutrons

“…1, that our measurement agrees well with the most recent (and most precise) published result for the β-asymmetry A 0 from the PERKEO II experiment [45][46][47], but is in poorer agreement with the three other results [40][41][42][43][44] employed by the Particle Data Group in their averaging procedure. Because of the differences between the PERKEO II and UCNA experimental techniques, we believe this is a significant result.…”

“…b The result reported in [42] superseded that reported in [41] of A 0 = −0.1116 (14), on the basis of a revised value for the polarization. c The final result reported in [44] was identical to a first result reported in [43].…”

“…The current status of published results [38][39][40][41][42][43][44][45][46][47] for the neutron β-asymmetry parameter A 0 is summarized in Table I and shown in Fig. 1.…”

“…Magnetic solenoidal spectrometers providing 2 × 2π solid angle acceptance for detection of the decay electrons were employed in the PERKEO [40] and PERKEO II [45][46][47] experiments at the Institut Laue-Langevin (ILL). In contrast, the solid angle was defined by the geometric acceptance in an experiment at the Petersburg Nuclear Physics Institute (PNPI) [41,42] in which the decay electrons and protons were detected in coincidence in detectors surrounding the beam decay region, and in an experiment at the ILL [43,44] which utilized a time projection chamber for reconstruction of the electron track. Results from measurements of the β-asymmetry parameter A0 [38][39][40][41][42][43][44][45][46].…”

“…1. Other than the UCNA Experiment, all of the experiments have been performed with beams of polarized cold neutrons, with reported values for the polarization ranging from 0.770 ± 0.007 [41,42] to 0.997 ± 0.001 [47]. Magnetic solenoidal spectrometers providing 2 × 2π solid angle acceptance for detection of the decay electrons were employed in the PERKEO [40] and PERKEO II [45][46][47] experiments at the Institut Laue-Langevin (ILL).…”