Reanalysis of the π½β $\overline{v}$ π 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 (π coefficient) in free neutron decay inferred from the recoil energy spectrum of the protons which are detected in 4β’π by the aSPECT spectrometer. With π=β0.104 02β’(82), the new value differs only marginally from the one published in 2020. Here, the experiment also has sensitivity to π, the Fierz interference term. From a correlated (π,π) fit to the proton recoil spectrum, we derive a limit of π =β0.0098β’(193) which translates into a somewhat improved 90% confidence interval region of β0.041 β€ π β€ 0.022 on this hypothetical term. Tighter constraints on π can be set from a combined analysis of the PERKEO III (π½ asymmetry) and aSPECT measurement which suggests a finite value of π with π (π) =β0.0181 Β± 0.0065 deviating by 2.82β’π from the standard model.