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The nEXO neutrinoless double beta (0νββ) decay experiment is designed to use a time projection chamber and 5000 kg of isotopically enriched liquid xenon to search for the decay in 136Xe. Progress in the detector design, paired with higher fidelity in its simulation and an advanced data analysis, based on the one used for the final results of EXO-200, produce a sensitivity prediction that exceeds the half-life of 1028 years. Specifically, improvements have been made in the understanding of production of scintillation photons and charge as well as of their transport and reconstruction in the detector. The more detailed knowledge of the detector construction has been paired with more assays for trace radioactivity in different materials. In particular, the use of custom electroformed copper is now incorporated in the design, leading to a substantial reduction in backgrounds from the intrinsic radioactivity of detector materials. Furthermore, a number of assumptions from previous sensitivity projections have gained further support from interim work validating the nEXO experiment concept. Together these improvements and updates suggest that the nEXO experiment will reach a half-life sensitivity of 1.35 × 1028 yr at 90% confidence level in 10 years of data taking, covering the parameter space associated with the inverted neutrino mass ordering, along with a significant portion of the parameter space for the normal ordering scenario, for almost all nuclear matrix elements. The effects of backgrounds deviating from the nominal values used for the projections are also illustrated, concluding that the nEXO design is robust against a number of imperfections of the model.

The levels in 26 Na with single particle character have been observed for the first time using the d( 25 Na,pγ) reaction at 5 MeV/nucleon. The measured

We report a precise determination of the 19 Ne half-life to be T 1/2 = 17.262 ± 0.007 s. This result disagrees with the most recent precision measurements and is important for placing bounds on predicted right-handed interactions that are absent in the current Standard Model. We are able to identify and disentangle two competing systematic effects that influence the accuracy of such measurements. Our findings prompt a reassessment of results from previous high-precision lifetime measurements that used similar equipment and methods.PACS numbers: 24.80.+y, 27.20.+n, 12.15.Hh, 29.40.Mc Precise measurements of decay rates and angular correlations in semi-leptonic processes are known to be excellent probes for interactions that are predicted by extensions of the Standard Model [1]. For example, the measured lifetime and electron asymmetry in neutron β decay [2] are used to probe for right-handed currents and obtain a precise value of V ud , the up-down element of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix, in a relatively simple system that is free of nuclear structure effects. However, in spite of this compelling advantage, precision neutron β decay experiments are challenging. Current results from independent neutron decay measurements show large discrepancies that need to be addressed before conclusive interpretations can be made from the data [2]. In this regard Nature offers a fortuitous alternative in 19