Magnetic trapping of neutrons

Accurate measurement of the lifetime of the neutron (which is unstable to b eta decay) is important for understanding the weak nuclear force(1) and the creation of matter during the Big Bang(2). Previous measurements of the ne utron lifetime have mainly been limited by certain systematic errors(3); ho wever, these could in principle be avoided by performing measurements on ne utrons stored in a magnetic tray. Neutral-particle and charged-particle tra ps are widely used for studying both composite and elementary particles, be cause they allow long interaction times and isolation of particles from per turbing environments(4). Here,ve report the magnetic trapping of neutrons. The trapping region is filled with superfluid He-4, which is used to load n eutrons into the trap and as a scintillator to detect their decay. Neutrons in the trap have a lifetime of 750(-200)(+330) seconds, mainly limited by their beta decay rather than trap losses. Our experiment verifies theoretic al predictions regarding the loading process and magnetic trapping of neutr ons. Further refinement of this method should lead to improved precision in the neutron lifetime measurement.