R- and N-correlation coe_cients in neutron decay: Search for scalar and tensor couplings in weak interactions

The decay correlation coe_cients R and N have been measured with the aim to search for scalar and tensor admixtures to the V-A interaction dominating in the neutron decay. Both R and N are accessible in the two transverse components of the electron polarization which was analyzed with Mott scattering from lead nuclei. The analysis of data collected in four runs is in its final stage giving the preliminary results consistent with the Standard Model: R = 0:005 _ 0:013(stat.) _ 0:005(syst.) and N = 0:064 _ 0:012(stat.) _ 0:004(syst.), respectively. A possible future experiment leading to an accuracy improved by at least an order of magnitude and more systematic investigation of the electron spin related correlation coe_cients is discussed as well.