Determination of the residue at the deuteron pole in an np phase-shift analysis.

Abstract

In an energy-dependent phase-shift analysis of all low-energy $\mathrm{np}$ scattering data below ${T}_{\mathrm{lab}}=30$ MeV we reach $\frac{{\ensuremath{\chi}}^{2}}{{N}_{\mathrm{DF}}}=1.1$, where ${N}_{\mathrm{DF}}$ is the number of degrees of freedom. In our fit we determine the $S$ matrix elements in the coupled $^{3}S_{1}+^{3}D_{1}$ channels, which allows us to compute the residue at the deuteron pole. Expressed in terms of the deuteron parameters, we find for the asymptotic normalization of the $^{3}S_{1}$ state ${A}_{S}=0.8838(4)$ ${\mathrm{fm}}^{\ensuremath{-}1/2}$ and for the asymptotic $\frac{D}{S}$ ratio $\ensuremath{\eta}=0.02712(22)$. Compared with other determinations, there seems to be some indication for the presence of closed isobar channels and/or energy-dependent potentials in the deuteron system.