Reanalysis of the β−ν¯e Angular Correlation Measurement from the aSPECT Experiment with New Constraints on Fierz Interference

On the basis of revisions of some of the systematic errors, we reanalyzed the electron-antineutrino angular correlation (a coefficient) in free neutron decay inferred from the recoil energy spectrum of the protons which are detected in 4 by the aSPECT spectrometer. With a=-0. 104 02 (82) the new value differs only marginally from the one published in 2020. The experiment also has sensitivity to b, the Fierz interference term. From a correlated (b, a) fit to the proton recoil spectrum, we derive a limit of b=-0. 0098 (193) which translates into a somewhat improved 90% confidence interval region of -0. 0410. 022 on this hypothetical term. Tighter constraints on b can be set from a combined shown as superscript (c) analysis of the PERKEO III (asymmetry) and aSPECT measurement which suggests a finite value of b with b^ (c) =-0. 01810. 0065 deviating by 2. 82 from the standard model.