H. R. Setze

Verification of the space-star anomaly in nd breakup

Abstract Cross-section measurements of a collinear configuration, the space-star and the coplanar-star configurations in nd breakup at E n = 13.0 MeV are reported. The present measurements for the collinear configuration are in good agreement with pd and nd data. Our coplanar-star data are consistent with theoretical predictions and resolve the reported problem with this configuration. The previously observed large discrepancy between theory and nd cross-section data for the space-star configuration is confirmed in the present work.

Implications of the space-star anomaly in nd breakup

Abstract Cross-section measurements of six exit-channel configurations in nd breakup at 13.0 MeV are reported and compared to rigorous calculations. Except for the coplanar-star configuration, our data are consistent with previous data. The present data for all configurations, with the exception of the space star, are in good agreement with theoretical predictions. The previously observed large discrepancy between theory and data for the space-star configuration is confirmed in the present work. The inclusion of the Tucson-Melbourne 2π exchange three-nucleon force with a cutoff parameter that correctly binds the triton only changes the predicted cross section by 2%, a factor of 10 smaller than the amount needed to bring theory into agreement with data.

Resolution of discrepancy between backward angle cross-section data for neutron-deuteron elastic scattering

High-accuracy differential cross-section data for neutron-deuteron elastic scattering at centre-of-mass backward angles in the range from 140° to 178° have been measured to accuracies better than ±3% for incident neutron energies of 8.0, 10.0, and 14.0 MeV. The measurements were made by detection of the recoil deuterons and protons from a mixed CD2-CH2 foil. The new data are compared to existing data and to three-nucleon calculations with the Bonn-B nucleon-nucleon potential. We conclude that the present measurements unambiguously resolve the discrepancies among previously reported data of the same type.

Neutron–proton analyzing power at 12 MeV and inconsistencies in parametrizations of nucleon–nucleon data

Abstract We present the most accurate and complete data set for the analyzing power A y ( θ ) in neutron–proton scattering. The experimental data were corrected for the effects of multiple scattering, both in the center detector and in the neutron detectors. The final data at E n = 12.0 MeV deviate considerably from the predictions of nucleon–nucleon phase-shift analyses and potential models. The impact of the new data on the value of the charged pion–nucleon coupling constant is discussed in a model study.

Scattering length measurements from radiative pion capture and neutron-deuteron breakup

The neutron-neutron and neutron-proton {sup 1}S{sub 0} scattering lengths a{sub nn} and a{sub np}, respectively, were determined simultaneously from the neutron-deuteron breakup reaction. Their comparison with the recommended values obtained from two body reactions gives a measure of the importance of three-nucleon force effects in the three-nucleon continuum. In order to check on the result obtained for a{sub nn} from the two-body {pi}{sup {minus}}-d capture reaction, a new measurement was performed at LANL. Preliminary results of the three experiments are given.

Cross-section measurements of the space-star configuration in N-D breakup at 13.0 MeV

In this paper we present results for kinematically complete cross‐section measurements of the space‐star configuration in neutron‐deuteron breakup for an incident neutron energy of 13.0 MeV. These data are a subset of the results obtained in a recent experiment in which cross sections for 46 configurations were measured simultaneously. The experimental techniques are described. These new data are in good agreement with previous n‐d data but differ significantly from both rigorous n‐d calculations and proton‐deuteron breakup data.

Probing the three-nucleon force using nucleon-deuteron breakup reactions

Abstract Results of our recent kinematically complete cross-section measurements of the space-star and coplanar-star configurations in n-d breakup at 13.0 MeV are reported. The experimental setup and details of the analysis are described. The new data for the space-star configuration are in good agreement with previous n-d data but differ significantly from both “exact” n-d calculations and p-d data. In constrast, the new coplanar-star data are in fair agreement with the calculations but are in gross disagreement with previous n-d data. The implications of these data for three-nucleon forces are discussed.

Neutron‐proton analyzing power at 12 MeV and charged πNN coupling constant

Recent reanalysis of scattering data by the Nijmegen group has led to new values for the πNN coupling constants, g2π°/4π and g2π±/4π, about 6% smaller than the previously accepted values. The impact of this finding is far reaching. Since the neutron‐proton Ay(θ) is dominated at low energies by the one‐pion‐exchange mechanism, accurate np data should provide unique information as to the magnitude of g2π±/4π. Using a new experimental setup consisting of a shielded neutron source, a five‐pair neutron detector array, a n‐4He polarimeter, and an intense polarized source with fast spin‐flipping capability, we have measured a 15 point angular distribution of the neutron‐proton Ay(θ) at and incident neutron energy of 12 MeV to a statistical accuracy of 5×10−4. We will discuss the data taking procedures, the analysis, and the corrections applied to the data. Preliminary results will be presented.

Selected Topics of the Few-Nucleon Research Program at TUNL

Results of kinematically-complete cross-section measurements of the n — d breakup reaction at E n = 13 MeV are reported. The new data for the space-star configuration of the three outgoing nucleons are in good agreement with previous data but are considerably different from rigorous n — d calculations. A status report on our n — n and n — p FSI measurements is given. New information about the importance of three-nucleon force effects in the n — d reaction is expected from these data. New data for the analyzing power in n — p scattering at E n = 12 MeV are presented. The preliminary analysis of these accurate data does not support the small value obtained by the Nijmegen group for the charged πN N coupling constant.