Still No Neutrinoless Double Beta Decay At PandaX-4T

Once again, there is no signal of neutrinoless double beta decay, which would indicate that the neutrino has a Majorana mass. 

This isn't necessarily decisive, because reasonable models of neutrinoless double beta decay rates for neutrinos with masses in the ballpark of what neutrino oscillation data and cosmology estimates would predict are still a few order of magnitude smaller than the ability of current experiments to detect (the predicted value is on the order of 10^28 years or more), although this due rule out less mainstream models of Majorana neutrinos which would predict much higher rates of neutrinoless double beta decay. But the consensus on non-detection from multiple experiments with different methods around the world does strongly discredit the one Russian experiment that claims to have seen this already many years ago, and it does deny advocates of Majorana mass for neutrinos any positive evidence that it exists.

We report the search for neutrinoless double-beta decay of 136Xe from the PandaX-4T experiment with a 3.7-tonne natural xenon target. The data reconstruction and the background modeling are optimized in the MeV energy region. A blind analysis is performed with data from the commissioning run and the first science run. No significant excess of signal over the background is observed. A lower limit on the half-life of 136Xe neutrinoless double-beta decay is established to be 2.1 × 10^24 ~ yr at the 90% confidence level, with a 136Xe exposure of 44.6 ~ kg⋅year. Our result represents the most stringent constraint from a natural xenon detector to date.

PandaX Collaboration, "Searching for Neutrinoless Double-Beta Decay of 136Xe with PandaX-4T" arXiv:2412.13979 (December 18, 2024).

The age of the universe is approximately 1.38 x 10^10 years. Xenon atoms would have been created sometime after Big Bang nucleosynthesis, no sooner than second generation stars. So, during the life of the universe, less than one in 10^14 atoms of the Xenon-136 isotope has had a neutrinoless double beta decay.

Footnote on Authorship in Collaborations

For what it is worth, I strongly endorse the emerging practice of designating a collaboration name, rather than merely a list of the names of everyone involved in the collaboration, as the primary author of papers that are the product of the work of the entire collaboration, which is fairly meaningless since it doesn't reveal the contributions of the individual authors to the collaboration. The only way that the contributions of the individual authors to the collaboration could really be meaningful is if collaborations did something similar to the credits of a movie, and broke down the individual collaborators by their job description within the collaboration.