Construction of a storage device for ultra-cold neutrons (UCN) using superconducting magnets in order to measure the lifetime of the free neutron

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The neutron lifetime n is one of the elementary natural constants and plays an important role in many fields of physics. For particle physics it is one of the fundamental quantities along with the correlations in neutron decay, namely the directions and spin of the decay products in reference to the helicity/spin of the neutron. One of these correlations together with the neutron lifetime enable us to test the unitarity of the Cabibbo-Kobayashi-Maskawa matrix and the Cabibbo model respectively. Furthermore, n plays a vital role in primordial nucleosynthesis having a big influence on the primordial helium abundance. Hence it influences the standard model of cosmology. The neutron lifetime has been measured repeatedly in the last decades, but there is still great uncertainty about the real value; the result of the most recent experiment deviated by more than 6  from the world average adopted by the Particle Data Group. To remeasure n, we want to store ultra-cold, thus very slow, neutrons (UCN) in a trap with magnetic walls created by superconducting coils. In this way collisions of the UCN with the material walls during the storage period are avoided and with them losses that result from reflections at these walls. In the storage volume of approx. 750 dm3 a big number of neutrons may be stored so that a statistical uncertainty of ∆n< 0.1 s is reached within short time. The neutron lifetime will be measured by recording both, the time distribution of the -decay protons in real-time and the number of neutrons surviving after different storage times. Probably the most essential properties of the proposed experiment are the handles on systematic effects together with good statistics: almost all of the storage parameters can be varied to study those effects in depth. We expect a total experimental uncertainty of less than 0.1 s.