Data on the Neutron–Neutron Scattering Length from the nd-Breakup Reaction at En = 8 MeV and En = 11 MeV

Abstract

A kinematically complete experiment devoted to studying the $$nd$$-breakup reaction at energies of 8 and 11 MeV via detecting all three secondary particles was performed. The $${}^{1}S_{0}$$ neutron–neutron ($$nn$$) scattering-length values of $$a_{nn}={-}19.8\pm 0.4$$ and $${-}19.0\pm 0.5$$ fm at, respectively, $$E_{n}=8$$ and $$11$$ MeV were obtained from a comparison of the experimental dependence of the yield of the $$nd$$-breakup reaction on the relative energy of the $$nn$$ pair with the results of a simulation. An analysis of the values obtained for the $$nn$$ scattering length, together with data from other experiments, confirms the hypothesis that three-nucleon forces affect the parameters of $$nn$$ interaction that are extracted from reactions involving few-nucleon systems and gives a new asymptotic $$nn$$ scattering length, $$a_{nn}={-}16.1\pm 0.1$$ fm.