We now know to within a tenth percent how long a neutron can survive without the atomic nucleus, before it decays into a proton.
This measurement is more precise than any previous measurements and represents a nearly two-fold increase in the lifetime of fundamental particles. This is important for understanding how the Universe's first matter was formed from a mixture of neutrons and protons in the seconds following the Big Bang.
Daniel Salvat, a nuclear physicist at Indiana University Bloomington, said that a neutron "decays" into a proton. This process involves the emission of a light-emitting electron and the emission of an almost massless neutrino.
"It is important to measure this value precisely because it can shed light on the origins of the universe and allow physicists discover flaws within our model of subatomic universe. We know they exist, but no one has been able find them."
Los Alamos National Science Center was the location of the research. There, a special experiment has been set up to measure neutron lifetimes. It's called the UCNtau project, and it involves ultra-cold neutrons (UCNs) stored in a magneto-gravitational trap.
The neutrons are chilled to almost absolute zero and then placed in the trap. This is a chamber with thousands of permanent magnetics that levitates the neutrons inside a vacuum jacket.
The magnetic field, which prevents neutrons depolarizing, and gravity together keep them from escaping, helps to keep the neutrons safe. This allows neutrons up to 11 days storage.
Researchers kept their neutrons in the UCNtau trap from 30 to 90 minutes. After that, they counted all remaining particles. They conducted repeated experiments between 2017-2019, counting over 40 million neutrons. This allowed them to obtain enough statistical data for the most precise determination of the particle's lifespan.
According to researchers' analysis, this lifespan is approximately 877.75 0.28 seconds (14 mins and 38 seconds). This refined measurement can be used to place important physical constraints on our Universe, such as the formation of dark matter and matter.
Things happened quickly after the Big Bang. The Universe's hot and dense matter cooled quickly into quarks, electrons, and protons within a few seconds.
The neutron's lifespan can be used to help physicists determine the role of decaying neutrons in the formation dark matter, the mysterious mass found in the Universe. This information can also help test the validity of something called the Cabibbo-Kobayashi-Maskawa matrix, which helps explain the behavior of quarks under the Standard Model of physics, the researchers said.
Salvat stated that neutron decay is explained by the quarks changing their identities. However, recent improvements in calculations indicate that this process may not be as predicted.
"Our new measurement will allow us to make an independent assessment of the neutron life, which could help settle the issue or provide evidence that would support the discovery of new physics."
The research was accepted by Physical Review Letters and is now available on arXiv.
