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
- 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
M. Beck, F. Ayala Guardia, M. Borg, J. Kahlenberg, R. Muñoz Horta, C. Schmidt, A. Wunderle, W. Heil, R. Maisonobe, M. Simson, T. Soldner, R. Virot, O. Zimmer, M. Klopf, G. Konrad, S. Baeßler, F. Glück, and U. Schmidt
(See online at https://doi.org/10.1103/physrevc.101.055506)
