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

Abstract

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. As a result of this approach and the use of a new in situ neutron detector, the lifetime reported here (877.7 $\pm$ 0.7 (stat) +0.4/-0.2 (sys) s) is the first modern measurement of ${\tau }_n$ that does not require corrections larger than the quoted uncertainties.

arXiv comment9 pages, 3 figures, 2 tables

References in corpus (10)

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• Improved Determination of the Neutron Lifetime
• Neutron lifetime measurements using gravitationally trapped ultracold neutrons
• Demonstration of a solid deuterium source of ultra-cold neutrons
• Performance of the upgraded ultracold neutron source at Los Alamos National Laboratory and its implication for a possible neutron electric dipole moment experiment
• Storage of ultracold neutrons in the UCN$\tau$ magneto-gravitational trap
• A new method for measuring the neutron lifetime using an in situ neutron detector
• A multilayer surface detector for ultracold neutrons
• Measurement of the neutron lifetime with ultra-cold neutrons stored in a magneto-gravitational trap
• Spin flip loss in magnetic confinement of ultracold neutrons for neutron lifetime experiments

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