Orateur
Description
The WISArD experiment is a high precision measurement of nuclear beta decay observables to test the existence of Physics Beyond the Standard Model in the weak sector. The angular correlation parameter $a_{\beta\nu}$ and the Fierz interference term $b$ in particular, are very sensitive probes to the existence of exotic scalar or tensor currents, which are not included in the standard V-A theory of the weak interaction. The goal of the WISArD experiment is to measure these parameters in the decay of $^{32}\mathrm{Ar}$ at the challenging level of precision of about 0.1%, at which they will provide constraints on new physics competitive with direct searches conducted at high energies at LHC. The experimental setup is installed in the ISOLDE experimental hall at CERN and received several $^{32}\mathrm{Ar}$ beamtimes over the past 8 years to reach this goal. The first one, in 2018, validated the principle of the measurement and the expected gain in sensitivity of the technique with respect to state of the art results. The world's third-best result on the angular correlation coefficient $a_{\beta\nu}$ was obtained in a single measurement of a pure Fermi decay. Following a full upgrade of the experimental setup and a second test beamtime in 2021, two experimental campaigns in 2024 and 2025 were successfully conducted, allowing to accumulate enough statistics to reach the required level of precision. A careful analysis of all sources of systematic errors has been carried out and no show-stopper has been identified yet. In this talk, we will present the final result of the WISArD measurement of the correlation parameter $a_{\beta\nu}$ from the 2024 and 2025 data takings and show how it compares with global constraints on exotic scalar currents.