How a extremely chilly tub can assist unravel the mysteries of the cosmos


A brand new “bathtub” experiment has allowed physicists to measure the lifetime of a free neutron way more exactly than ever earlier than. The breakthrough may assist probe the fringes of the Normal Mannequin of particle physics, in addition to mysteries like darkish matter and the early levels of the universe.

Neutrons are principally discovered within the nucleus of atoms, however they may also be produced on their very own via processes like nuclear reactions or cosmic rays interacting with atoms within the environment. These “free neutrons” are unstable and can decay right into a proton, electron and antineutrino – however precisely how lengthy that course of takes is contentious.

Physicists measure the common lifetime of free neutrons utilizing one in all two predominant strategies – a “bottle” or a “beam.” The previous includes placing free neutrons in a bottle-like instrument, ready a sure period of time, then counting what number of stay. The latter includes producing a beam of neutrons, then counting what number of protons are produced because the neutrons decay. Frustratingly, the 2 strategies constantly supply totally different values – bottle neutrons reside about 14 minutes and 39 seconds on common, in comparison with 14 minutes and 48 seconds for beamed neutrons.

9 seconds may not sound like a serious discrepancy, but it surely has large implications for a spread of necessary calculations in physics. Even weirder, the distinction has solely grown wider as every methodology turns into extra exact, and there isn’t any overlap between their ranges. This might point out that one approach is doing one thing flawed, scientists are overestimating their certainty – or that unknown physics are interfering.

“The method by which a neutron ‘decays’ right into a proton – with an emission of a light-weight electron and an nearly massless neutrino – is likely one of the most fascinating processes recognized to physicists,” says Daniel Salvat, lead investigator of the examine. “The trouble to measure this worth very exactly is important as a result of understanding the exact lifetime of the neutron can make clear how the universe developed – in addition to enable physicists to find flaws in our mannequin of the subatomic universe that we all know exist however no person has but been capable of finding.”

Scientists now say they’ve measured the lifetime of the free neutron extra exactly than ever earlier than. At Los Alamos Nationwide Laboratory, the crew arrange an experiment referred to as UCNtau, which is a variation on the bottle methodology which they name a “bathtub.”

Neutrons are cooled to nearly absolute zero – UCN stands for “Ultracold Neutrons” – then positioned into an instrument that levitates them with 1000’s of magnets. After 30 to 90 minutes, the scientists depend the surviving neutrons to calculate their common lifetime. Utilizing this methodology, the crew counted round 40 million neutrons over two years, to lastly attain their determine.

In response to the brand new examine, the common lifetime of a free neutron is 14 minutes and 37.75 seconds. The researchers say they’ve measured this with greater than twice the precision of earlier measurements, bringing the uncertainty down to simply 0.039 p.c.

The crew says that understanding this determine extra exactly can inform an enormous vary of necessary questions in cosmology and physics, resembling how the primary atomic nuclei had been fashioned, and the relative quantities of parts created within the early universe. There’s even an opportunity that neutrons decay into darkish matter, which may clarify the discrepancy between bottle and beam measurements.

The analysis was printed within the journal Bodily Evaluate Letters.

Supply: American Bodily Society through Phys.org



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