Measurement of the neutron lifetime using a hybrid magnetic trap for ultra-cold neutrons

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The neutron lifetime τn is a basic observable that not only determines the light-element abundances in big-bang nucleosynthesis but is also a key ingredient for understanding weak interactions within the framework of the Standard Model of particle physics. In this respect the neutron lifetime is the most important complement to the angular correlations which are the scope of the new instrument PERC. A recent experiment with quoted uncertainty of only 0.8 seconds has generated a confusing situation: its result for τn deviates from the previous world average by more than seven seconds. Since most precise past experiments employed storage of ultra-cold neutrons (UCN) in material bottles, the discrepancy calls for an approach with different systematic. Our goal is thus to measure τn within this funding period with accuracy well below 1 s, using a novel method with live detection of electrons from neutron decay within a magneto-gravitational UCN trap, coupled to a new high-density UCN source.