A re-evaluation of a 2005 measurement of the lifetime of the neutron has deepened the mystery of why two different experimental techniques yield two different neutron lifetimes. After recalibrating a key part of their "beam" experiment, physicists in the US confirmed that their value for the neutron lifetime is 8 s longer than that determined by others who had done a "bottle" experiment. What is more, this latest result puts the statistical significance of the discrepancy at nearly 4σ, making it unlikely to be a random anomaly.

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