The mysteries of the cosmos ... revealed by a super cold bath

Neutrons are found mainly in the nucleus of atoms, but they can also be produced by themselves through processes such as nuclear reactions or cosmic rays that interact with atoms in the atmosphere. These "free neutrons" are unstable and will decay into a proton, an electron and an antineutrino, but exactly how long this process takes is still unclear. Physicists currently measure the lifespan of free neutrons using two main methods. Unfortunately, however, the two techniques constantly offer different values: in the first case the neutrons live on average about 14 minutes and 39 seconds, in the second 14 minutes and 48 seconds. Nine seconds may not seem like a big discrepancy, but it does have huge implications for a number of important calculations in physics. Even more oddly, the difference grew as each of the two methods became more precise. This could indicate that a technique is doing something wrong, scientists are overestimating their certainty or unknown physical phenomena are interfering.

credits: Los Alamos National Lab Scientists from Los Alamos National Laboratory, however, claim to have succeeded to measure the duration of the free neutron in a more precise way, by creating an experiment called UCNtau, which is a variation of the bottle method they call "bathtub".

In it, neutrons are cooled to almost zero absolute - UCN stands for “Ultracold Neutrons” - then placed in an instrument that makes them levitate with thousands of magnets. After 30-90 minutes, scientists count the surviving neutrons to calculate their lifespan. Using this method, the team counted around 40 million neutrons over two years, reaching the result of 14 minutes and 37.75 seconds. The researchers say they measured it with more than double the accuracy of previous measurements, bringing the uncertainty to only 0.039%.

The team says that understanding this phenomenon more precisely can provide answers to a wide range of important questions in cosmology and physics, such as how the first atomic nuclei formed and the relative quantities of elements created in the early universe. There is also the possibility that neutrons decay into dark matter, which could explain the discrepancy between the measurements of the two types of classical experiments.