Precision measurement of the angular correlation coefficient a in neutron beta-decay
Final Report Abstract
In summary, we have measured the evβ−angular correlation coefficient a with aSPECT resulting in a fractional precision of ~ 0.8 %. This result is in good agreement with the present PDG value but with the overall accuracy improved by a factor of 3.3. Within the SM, the correlation coefficients in neutron ß-decay can be expressed in terms of one parameter, λ, which is the ratio of the weak coupling constants: λ = gA/gV. With a = -0.10430(84) we obtain λ= -1.2677(28). This value deviates by 2.8 σ from the most recent λ measurement of the PERKEO III collaboration, which was determined via the ß-asymmetry parameter A. This experimental situation calls for further improvements in the measurement accuracy; in particular being on par with the Perkeo result in terms of accuracy presents a major challenge. The 4π detection of the decay protons with the aSPECT spectrometer which is based on the electrostatic MAC-E filter principle helps to a great deal to suppress unwanted systematics. From the analysis of the systematic effects we are confident that with an upgrade of the present spectrometer, a relative accuracy of Δa/a ~ 0.2% can be reached.
Publications
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Improved determination of the β−νe angular correlation coefficient a in free neutron decay with the aSPECT spectrometer. Phys. Rev. C 101, 055506 – 26 May 2020
Beck, M.; Ayala Guardia, F.; Borg, M.; Kahlenberg, J.; Muñoz Horta, R.; Schmidt, C.; Wunderle, A.; Heil, W.; Maisonobe, R.; Simson, M.; Soldner, T.; Virot, R.; Zimmer, O.; Klopf, M.; Konrad, G.; Baeßler, S.; Glück, F. & Schmidt, U.
