When part of an atomic nucleus, neutrons are extremely stable, but 'free' neutrons (i.e. those outside of a nucleus) decay into a proton, an electron and an electron-antineutrino in about 15 minutes.
Two different methods have been used to measure the neutron's 'lifespan'.
The 'bottle' method and the 'in-beam' method (described in the links below) give different results. The bottle method puts the decay time at 878.5 seconds ±1 second. With the beam method it's 887.7 seconds ±1.9 seconds.
Not only do the results differ by more than 9 seconds, but also the 'margin of error' figures don't fit into the difference. So either the measurements are wrong, or the error margin is wrong, or both.
Although the 9 seconds difference may seem marginal, it has very far-reaching implications for calculations regarding the, where neutrons and protons are believed to have been forming within 20 minutes or so of the event, and when the (lighter) elements were created.
See: Neutron death mystery Scientific American, May 2014
Further tech info :
Improved Determination of the Neutron Lifetime Phys. Rev. Lett. 111, 222501
Toward New Precision in Measuring the Neutron Lifetime NIST Center for Neutron Research
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