A determination of the singlet neutron-neutron scattering length from the 2H(n, p)2n reaction

Abstract

The proton energy differential cross section d 2σ dΩ d E p in the 2H(n, p)2n reaction at 14.1 MeV has been accurately measured at the mean proton angle \\ ̄ gq p = 4.0° ± 2.2° with a counter telescope consisting of two Si(Li) surface-barrier detectors and three gas proportional counters. Detailed descriptions on the experiment have been presented. In order to extract the 1S o n-n scattering length a nn , the measured break-up proton spectrum was compared in detail by the χ 2 minimization with the theoretical spectrum calculated in the framework of the Faddeev approach using the separable potentials. As the result, we obtained a nn = − 18.31 ± 0.22 fm with the effective range r nn = 2.84 fm which was fixed in this analysis. This value of a nn is comparable with the value predicted by Noyes and Lipinski who summarized recently the n-p and p-p scattering parameters. The assumption of charge independence of nuclear forces has been evidently violated. The a nn values deduced until now have been summarized, and it has been discussed that the a nn values extracted from the analysis based on the conventional approximations are unreliable at least at 14 MeV.