At the April 13th and 14th meeting of the American Physical Society in Denver, Co. Physicists debated new ways to determine how long neutrons actually live [scientificamerican.com]. While neutrons are typically bound up with protons in the nucleus of atoms, and are perfectly stable there, they don't last long on their own.
Depending on the approach taken to measure it, the average lifetime of a neutron returns different values.
Using the bottle method (put a bunch of Neutrons in a 'bottle' and count how many are left after a period of time), the average lifetime is 14 minutes, 39 seconds.
Using the 'beam' method (count the protons given off in a detector as neutrons decay), the average lifetime is 14 minutes, 47 seconds.
These two methods are so precise that they do not overlap even taking the worst possible margins of error of both. It is a puzzler.
"The discrepancy has bedevilled researchers for nearly 15 years."
One possibility is that one of the two methods is doing something wrong. In that case, researchers might want to combine beam and bottle in a single device. At the meeting, physicist Zhaowen Tang of the Los Alamos lab described how researchers could put a particle detector inside a bottle neutron trap and count neutrons using both methods. His team has acquired funding to start building the device.
Another possibility is that the beam and bottle approaches have been measuring the neutron lifetime correctly, but that some unseen factor accounts for the discrepancy between the two. A leading idea is that neutrons might occasionally decay into not just protons but also dark matter, the mysterious unseen material that makes up much of the Universe’s matter.
Interesting that plain old neutrons might be the key to opening the door on dark matter.
Pinpointing the lifetime of a neutron is important for understanding how much hydrogen, helium and other light elements formed in the first few minutes after the Universe was born in the Big Bang, 13.8 billion years ago. Scientists also think they can hunt for new types of physics if they can better pin down the neutron’s lifetime, because that would help to constrain measurements of other subatomic particles.
A few seconds goes a long way in physics.