Speaker
Description
Measurements of neutron decay parameters can provide the value of the CKM matrix element Vud, which dominates its first row. Thanks to comparatively small theoretical uncertainties, such measurements have the potential to surpass the current most precise methods using nuclear decays and enable the most sensitive test of CKM unitarity. However, various discrepancies between previous results from neutron decay have been limiting the precision reach.
The Nab spectrometer installed at the Fundamental Neutron Physics Beamline of the Spallation Neutron Source is measuring the electron-neutrino correlation parameter ‘a’ in the decay of free, unpolarized neutrons, with the goal to achieve world-leading precision. This parameter, together with measurements of the neutron lifetime, determines Vud. A follow-on measurement of correlations in decays of highly polarized neutrons (‘pNAB’) has the potential to resolve discrepancies between previous correlation measurements with unpolarized and polarized neutrons and provide a measurement of Vud---and a CKM unitarity test---with world-leading precision. Additionally, the spectrometer is sensitive to effects beyond the Standard Model theory of the weak interaction.
This presentation will introduce the Nab spectrometer, provide results of the successful commissioning run, and discuss the path towards reaching the ultimate precision with Nab and eventually pNAB.
