Determination of Low-Energy Parameters of Neutron--Proton Scattering on the Basis of Modern Experimental Data from Partial-Wave Analyses

The triplet and singlet low-energy parameters in the effective-range expansion for neutron--proton scattering are determined by using the latest experimental data on respective phase shifts from the SAID nucleon--nucleon database. The results differ markedly from the analogous parameters obtained on the basis of the phase shifts of the Nijmegen group and contradict the parameter values that are presently used as experimental ones. The values found with the aid of the phase shifts from the SAID nucleon--nucleon database for the total cross section for the scattering of zero-energy neutrons by protons, $\sigma_{0}=20.426$b, and the neutron--proton coherent scattering length, $f=-3.755$fm, agree perfectly with the experimental cross-section values obtained by Houk, $\sigma_{0}=20.436\pm 0.023$b, and experimental scattering-length values obtained by Houk and Wilson, $f=-3.756\pm 0.009$fm, but they contradict cross-section values of $\sigma_{0}=20.491\pm 0.014$b according to Dilg and coherent-scattering-length values of $f=-3.7409\pm 0.0011$fm according to Koester and Nistler.Comment: 17 pages, to be published in Physics of Atomic Nucle