Physicists Have Made the Most Precise Neutron Lifespan Measurement Ever

This could help reveal how the infant universe evolved into ours.
Brad Bergan
A computer-generated image of an atom.cokada / iStock

We just took a step closer to unraveling the mysteries of the universe.

A team of researchers has achieved the most precise measurement ever taken of the lifespan of a neutron, according to a study recently shared to a preprint server.

However, a discrepancy between measurement methods remains unsolved.

The most precise measurement of neutron decay

Neutrons are a type of particle that usually remain inside atoms. They exist for billions of years longer inside some atoms composing the cosmos, but when separated from the atom, they begin to decay into protons and other, more basic particles. And, separated from their host atoms, neutrons only last for about 15 minutes. Physicists have tried to measure the precise lifetime of a neutron for decades, primarily implementing two techniques. The first one uses bottles, and the other employs beams. But results from either didn't match, showing a difference of 9 seconds -- an eternity in atomic timeframes, and significant in our own, since we're talking about a particle that only "lives" for 15 minutes.

However, the new study managed to find the most precise measurement of a neutron's lifetime with the bottle technique. The experiment, called UCNtau (or, Ultra Cold Neutrons tau, the latter of which stands for the neutron lifetime), and revealed that a neutron lives for precisely 14.629 minutes, at an uncertainty of roughly 0.005 minutes. Incredibly, this is twice as precise than earlier measurements taken with either method. The newest results don't solve the enduring mystery of why the results for the bottle and beam methods are incommensurate, but they've taken us one step closer to a real answer. "This new result provides an independent assessment to help settle the neutron lifetime puzzle," said Francis L. Moseley Professor of Physics Brad Filippone, of Caltech, who is a co-author of the recent study, in a university post.

Unfolding the mysteries of the early universe

The two methods continue to show a mutual discrepancy, but Filippone thinks it's either because one of them might be faulty, or because there's something lying in the physics, awaiting our future discovery. "When combined with other precision measurements, this result could provide the much-searched-for evidence for the discovery of new physics," he added. The results might also shed light on other enduring mysteries of physics, like how matter in the early universe first congealed out of the unconscionably hot soup of neutrons and additional particles. "Once we know the neutron lifetime precisely, it can help explain how atomic nuclei formed in the early minutes of the universe."

The UCNtau team performed two bottle experiments in 2017 and 2018 at the Los Alamos National Laboratory (LANL). During the bottle method, free neutrons are contained in an ultracold and magnetized bottle that's roughly the size of a bathtub. Once trapped within, the neutrons begin to decay into protons. Highly advanced data analyses methods enable the researchers to count how many neutrons remain as the seconds pass. By contrast, the beam method uses a literal beam of neutrons that decays into protons, where the protons, instead of the neutrons, are counted. The UCNtau collaboration has counted a mind-numbing number of 40 million neutrons since the experiments began, according to the Caltech post. And as further features of neutron decay and the discrepancy between measurement methods are revealed, a little more of the universe will unfold.

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