Measurements of np observables at TRIUMF

Recent np elastic scattering measurements at TRIUMF have emphasized high precision and extension of the data base to include previously only poorly measured observables. The measurements are: Aoonn, Aoono, Aooon over many angles; Rt=Aosso at one angle near 160 degree c. m.; Dt/Rt =Aonno/Aosso at one angle near 160 degree c. m.; Aoono zero crossing angles and n+p → p+n differential cross section at 0 degree; all at several energies over the TRIUMF energy range (200--500 MeV). These measurements were undertaken to improve the np phase shifts, which have yet to reach the precision of the pp phase shifts, and to help resolve discrepancies in the np data set. The present data, that have been analyzed to date, constrain the 3S1-3D1 mixing parameter, ε1, to the lower end (about 4 degree) of its previous range; also lower ε3; and smooth out the energy variation of the 1P1, 3S1, and 3D2 phase shifts. The measured elastic scattering observables are important in distinguishing the predictions of the modern N-N potentials needed for nuclear structure calculations