Limit on the Fierz Interference Term b from a Measurement of the Beta Asymmetry in Neutron Decay

A new neutron lifetime experiment with cold neutron beam decay in superfluid helium-4

“…Furthermore, while the intrinsic UCN storage time τ (0) tot is being measured in the storage volume filled with isotopically pure liquid 4 He, the neutron beta decay spectrum can be simultaneously obtained in the decay volume at a good resolution and accuracy with this detector. It may provide a measurement on the Fierz interference term b in the energy dependent neutron beta decay rate at a potentially high precision compared to the most recent results [45].…”

Corrections of order O(E^2_e/m^2_N), caused by weak magnetism and proton recoil, to the neutron lifetime and correlation coefficients of the neutron beta decay

“…The structure and the value of the Fierz interference term may depend on interactions beyond the SM. A recent information of the theoretical and experimental status of the Fierz interference term can be found in [33,34,[42][43][44].…”

“…We would like to notice that all corrections of order O(E 2 e /m 2 N ) to the correlation coefficients D(E e ), R(E e ) and L(E e ) are either equal to zero or much smaller than 10 −5 . The corrections to the Fierz interference term b(E e ) we do not consider, since up to now its experimental status is not well defined [33,34,[42][43][44]. Using the standard procedure for the calculation of the electron-energy and angular distribution of the neutron beta decay (see, for example, Appendix A in [18]) we obtain the following analytical expressions for the corrections…”

“…Together with Wilkinson's corrections [15] (see also [18,[25][26][27][28]) and radiative corrections of order O(αE e /m N ) ∼ 10 −5 [29,30], the corrections O(E 2 e /m 2 N ) ∼ 10 −5 should provide an improved level of precision of the theoretical background of the neutron beta decay, calculated in the SM. It is initiated to promote experimental searches of contributions of interactions beyond the SM [8,[31][32][33][34][35] with experimental sensitivities of about a few parts of 10 −5 .…”

Electrodisintegration of Deuteron into Dark Matter and Proton Close to Threshold

“…We would like to emphasize that a possibility to explain the NLA problem by the neutron dark matter decay mode n → χ + ν e + νe is not innocent and demands to pay the following price. As has been pointed out in [9], the explanation of the neutron lifetime τ n = 888.0(2.0) s [1] within the Standard Model with the axial coupling constant g A = 1.2764 [28,29], reproducing the neutron lifetime τ n = 879.6(4) s [30], is not possible and demands the account for the contributions of interactions beyond the Standard Model such as the Fierz interference term b [31][32][33][34][35][36][37][38] equal to b = −1.44 × 10 −2 [39]. However, as has been shown in [39], the Fierz interference term b = −1.44 × 10 −2 does not contradict the existing experimental data on the correlation coefficients and asymmetries of the neutron beta decay.…”