The exact lifetime of the neutron is known

An international group of physicists led by researchers from Indiana University in Bloomington has announced the world’s most accurate measurement of the neutron lifetime. This is reported by journal Physical Review Letters.

Physicists who work as part of the UCNtau experiment have announced another achievement. The goal of the project is to measure the lifetime of a free neutron with maximum accuracy, and scientists have recently succeeded. According to the latest data, its lifetime is 877.75 ± 0.28 seconds (that’s 14 minutes 38 seconds). It is worth noting that the accuracy of the new measurements is twice as high as the previous ones. This is important for understanding the processes of formation of matter in the Universe in the first moments after the Big Bang.

The neutron is one of the building blocks of matter. This heavy particle is a neutral analogue of an elementary particle, a positively charged proton. Like many other subatomic particles, it can remain outside the core for a long time. In about 15 minutes, it decays into a proton, an electron and a tiny particle – an antineutrino.

The problem is that the data is only approximate. There are two ways to change the decay time of a neutron. The first (the “beam” method) gives the result in 887.7 ± 2.2 seconds, the second (the “bottle” method) – 878.5 ± 0.8 seconds. It is the nine-second difference that confuses scientists.

Scientists hope to get a single-digit number for determining the neutron’s lifetime so that it can be included in various equations describing the universe. Uncertainty is acceptable, but when it is less than a second. However, getting certainty on just one number proved to be more difficult than physicists had anticipated.

In the new study, they used a fundamentally new measurement method.

At Los Alamos National Laboratory, scientists conducted the UCNtau experiment, which is a variation of the bottle method that physicists have called the bath method. Usually free neutrons are placed in a bottle-like vessel (hence the name). Scientists wait for a certain time and then count the number of survivors.

In a new experiment with a “bath”, neutrons are cooled to near absolute zero, and then placed in a device that lifts them into the air using thousands of magnets. After 30–90 minutes, scientists counted the number of surviving neutrons to determine their average lifetime. Using this method, the team calculated about 40 million neutrons in two years.

According to new research, the average lifetime of a free neutron is 14 minutes 37.75 seconds. The margin of error is only 0.039%.

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Alexandr Ivanov earned his Licentiate Engineer in Systems and Computer Engineering from the Free International University of Moldova. Since 2013, Alexandr has been working as a freelance web programmer.
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Alexandr Ivanov

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