Limit on the Fierz Interference Term b from a Measurement of the Beta Asymmetry in Neutron Decay

• Published in: Physical review letters Vol. 125; no. 11; pp. 1 - 112501
• Main Authors: Saul, H., Roick, C., Abele, H., Mest, H., Klopf, M., Petukhov, A. K., Soldner, T., Wang, X., Werder, D., Märkisch, B.
• Format: Journal Article
• Language: English
• Published: College Park American Physical Society 11-09-2020
• Subjects: Axial stress; Beta rays; Couplings; Decay rate; Interference; Neutron decay; Particle decay; Particle physics; Standard model (particle physics); Tensors
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.125.112501

In the standard model of particle physics, the weak interaction is described by vector and axial-vector couplings only. Nonzero scalar or tensor interactions would imply an additional contribution to the differential decay rate of the neutron, the Fierz interference term. We derive a limit on this hypothetical term from a measurement using spin-polarized neutrons. This method is statistically less sensitive than the determination from the spectral shape but features much cleaner systematics. We obtain a limit of b=0.017(21) at 68.27% C.L., improving the previous best limit from neutron decay by a factor of four.