Using the covariant spectator theory (CST), we present two one-boson-exchange kernels that have been successfully adjusted to fit the 2007 world $\mathit{np}$ data (containing 3788 data) below 350 MeV. One model (which we designate WJC-1) has 27 parameters and fits with a ${\ensuremath{\chi}}^{2}/{N}_{\mathrm{data}}=1.06$. The other model (designated WJC-2) has only 15 parameters and fits with a ${\ensuremath{\chi}}^{2}/{N}_{\mathrm{data}}=1.12$. Both of these models also reproduce the experimental triton binding energy without introducing additional irreducible three-nucleon forces. One result of this work is a new phase-shift analysis, updated for all data until 2006, which is useful even if one does not work within the CST. In carrying out these fits we have reviewed the entire database, adding new data not previously used in other high precision fits and restoring some data omitted in previous fits. A full discussion and evaluation of the 2007 database is presented.

http://inspirehep.net/record/779208/files/arXiv:0802.1552.pdf

Covariant spectator theory of np scattering: Phase shifts obtained from precision fits to data below 350-MeV

Using the delta-shell representation we present a successful fit to neutron-proton and proton-proton scattering data below pion production threshold. A detailed overview of the theory necessary to calculate observables with this potential is presented. A new data selection process is used to obtain the largest mutually consistent data base. The analysis includes data within the years 1950 to 2013. Using 46 parameters we obtain chi^2/Ndata = 1.04 with Ndata = 6713 including normalization data. Phase shifts with error bars are provided.

Coarse-grained potential analysis of neutron-proton and proton-proton scattering below the pion production threshold

Research on the two-nucleon problem during the period 1959-1971 is reviewed and the status of this field is assessed. An attempt is also made to give a complete bibliography covering this period. This review was completed in August 1972.

http://iopscience.iop.org/article/10.1088/0034-4885/35/2/303/pdf

The interaction of two nucleons

The neutron elastic scattering cross sections for lead, cadmium, copper, aluminium, oxygen, nitrogen, carbon, beryllium and lithium have been measured for an effective neutron energy of 136 Mev. A large liquid scintillator was used, and the cross sections were obtained on an absolute scale. The integrated total elastic cross sections are consistent with previous measurements of total and inelastic cross sections.

CIII. The elastic scattering of 136 MeV neutrons by nuclei

The free neutron-proton polarization has been measured at centre-of-mass angles from 20° to 160°. The asymmetries were obtained using fixed detectors and by rotating the plane of polarization of the neutron beam with respect to the scattering plane by means of a long solenoid. The polarization cross-section was found to be strongly non-antisymmetrical about 90° centre-of-mass and evidence forD-wave interaction was obtained.

Polarization in neutron proton scattering at 95 MeV

Neutron-proton scattering has been measured from 6 to 61$\cdot $5 degrees c.m. for neutrons of effective energy 105 $\pm $ 3 and 137 $\pm $ 5 MeV using a liquid hydrogen scatterer and a large neutron counter. The results confirm previous measurements and show a near symmetry around 90 degrees at 105 MeV, and a fairly definite asymmetry at 137 MeV. The 'Serber force' does not, therefore, give a good approximation to the experimental data at 137 MeV.

Neutron-Proton Scattering at Small Angles

Total absorption cross-sections of hydrogen, carbon, copper, silver, lead and uranium have been measured for photons of mean energy 94 MeV. The method was to measure the transmission through an absorber of photons from the Oxford synchrotron, using a biased liquid scintillation counter to select photons of energy near the peak energy of the machine. The experimental data for hydrogen have been used to deduce a value for the cross-section for pair production in the field of the electron of 4$\cdot $7 $\pm $ 0$\cdot $4 millibarn. The relative cross-sections for the heavier elements have been determined to better than $\pm $ 0$\cdot $2%, and confirm the most recent calculations of the correction to the Born approximation in the theory of pair production.

J. J. Thresher

Papers

Neutron-Proton Scattering at Small Angles

The Absorption of High-Energy Photons in Matter