Data on Neutron–Neutron Scattering Length from the Reaction $n{+}^2\text{H}\to n+n+p$ at $E_n=60$ MeV

The ${}^1{S}_0$ neutron–neutron ($nn$) scattering length was measured in the neutron–deuteron ($nd$) breakup reaction at an energy of 60 MeV. The respective experiment was performed in the geometry of final-state interaction via detecting all three secondary particles. The scattering-length value of $a_{nn}=-16.3\pm 0.5$ fm was determined on the basis of a comparison of the experimental dependence of the $nd$-breakup reaction yield on the relative energy of the $nn$ pair with the results of a simulation. An analysis of this scattering-length value, together with data obtained in other experiments devoted to studying $nd$ and $dd$ breakup, confirms the hypothesis that three-nucleon forces affect the values extracted from data on these reactions for the parameters of the $nn$ interaction.