Precision measurements of neutron decay offer complementary access to particle physics at small distance scales or high energies. In particular they allow tests of the V-A structure of the weak interaction. Among many experimental activities which are ongo

Stephan Paul

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G V

G2

V·(1−3λ2)

Experimentally two different approaches have been taken to measure the neutron lifetime.

•Until the late eighties most experiments have used the in-beam method which re-quires the detection of n-decay products from a well definedfiducial volume.Al-though being competitive on the statistical accuracy this method faces many sys-tematic problems which has limited thefinal precision of the experiments.

•The most precise experiments have been performed using the method of stored neutrons.Ultra cold neutrons(UCN)can be confined in bottles by means of their interaction with the surface,the gravitationalfield and magneticfield gradients.

Choosing proper materials neutrons are reflected from the surface with minimal losses which may occur either by absorption or by up-scattering(in which case they gain sufficient energy to leave the containing volume).The maximal allowed energies of such neutrons is around250-300neV.The neutron lifetime is derived