New Attempt to Determine then−nScattering Length with theH2(n,np)nReaction

The $n-n$ final-state interaction (FSI) was investigated via the ${}^2\mathrm{H}(n,np)n$ reaction at 25 MeV, using a geometry which enables the simultaneous observation of $n-p$ quasifree (QFS) scattering. The data were analyzed with Monte Carlo simulations based on rigorous Faddeev calculations with realistic nucleon-nucleon potentials. The value of $a_{\mathrm{nn}}$ deduced from the absolute yield in the FSI peak is $-16.27\mathrm{}\pm 0.40\mathrm{fm}$ while the relative data, normalized in the QFS region, give $-16.06\mathrm{}\pm 0.35\mathrm{fm}$. Thus our results differ from the “recommended” value of $a_{\mathrm{nn}}=-18.5\mathrm{}\pm 0.3\mathrm{fm}$ by more than 5 standard deviations.