On triplet low-energy parameters of nucleon-nucleon scattering

Triplet low-energy parameters of neutron-proton scattering, including high-order shape parameters, are calculated on the basis of approximating the effective-range function k cot delta(t) by polynomials and rational functions with the aid of the latest experimental data on phase shifts from the SAID nucleon-nucleon database. With the resulting values of the low-energy parameters, a good description of phase shifts over a broad energy interval is obtained by using the effective-range expansion featuring a small number of terms. The properties of the deuteron that were calculated on the basis of the values found for the triplet low-energy parameters of scattering agree very well with experimental values. The triplet low-energy parameters and the properties of the deuteron that were obtained here by using present-day data from the SAID database differ markedly from the analogous results obtained for data of the Nijmegen group. Possible reasons behind this discrepancy are discussed. Highly precise new approximate formulas for determining the shape parameter v(2) are proposed and are shown to be efficient in calculations. The effective-range expansion for the D wave is considered, and preliminary results of calculations of low-energy scattering parameters for this case are obtained.