Measurement of the neutron lifetime using an asymmetric magneto- gravitational trap and in situ detection

Understand

The precise value of the mean neutron lifetime, $\tau_n$, plays an important role in nuclear and particle physics and cosmology.

• It is a key input for predicting the ratio of protons to helium atoms in the primordial universe and is used to search for new physics beyond the Standard Model of particle physics.
• There is a 3.9 standard deviation discrepancy between $\tau_n$ measured by counting the decay rate of free neutrons in a beam (887.7 $\pm$ 2.2 s) and by counting surviving ultracold neutrons stored for different storage times in a material trap (878.5$\pm$0.8 s).
• The experiment described here eliminates loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls and neutrons in quasi-stable orbits rapidly exit the trap.