The PSI np Data and their Effect on the Charged pNN Coupling Constant

Abstract

Differential cross sections of elastic neutron-proton scattering have been measured for the energy range from 200 MeV to 580 MeV. The angular interval for the detection of the recoiling proton ranges up to 48 • in the laboratory system. This corresponds to an interval of the scattering angle from 80 • to 180 • in the centre-of-mass system. For absolute normalization the simultaneously measured np → dπ o reaction was used above 280 MeV. The charged πNN coupling constant has been determined to f 2 πnp = 0.076 ± 0.001.

Angle-dependent normalization of neutron-proton differential cross sections

“…Also some other np differential cross section measurements appeared to have systematic errors similar (but not identical) to the Uppsala data; the Princeton [6] and Freiburg [7,10] data are prominent examples.…”

“…Some flaws, on the other hand, are so serious that their contribution to χ 2 dominates over the statistical contribution to the extent that the standard rules of statistics no longer apply. Consequently, such data sets [6][7][8][9][10] must be excluded from the databases used in PWA's. This is of course an unfortunate and undesirable situation, especially in view of the waste of investment and effort involved in these experiments.…”

“…This implies that these data sets can, instead of discarding them, from now on be included in the np database. The salvation of these systematically-flawed data sets [6][7][8][9][10] is a major accomplishment of our adnorm method.…”

9. The nucleon-nucleon interaction

“…Among the more technical problems is the neutron-neutron scattering length where experiments are still in contradiction. There are problems with the determination of a precise value for the πN N coupling constant and, not unrelated, the huge and expensive database of neutron-proton differential cross sections [104,105,84,100] is inconsistent.…”

“…Particular attention deserve the TUNL data on ∆σ L and ∆σ T between 5 and 20 MeV [91] which made it possible to pin down the ǫ 1 mixing parameter with unprecedented precision. Table 9 includes several new measurements of np differential cross sections (σ), with the largest sets produced by the Freiburg group [100] (871 data between 200 and 350 MeV), the Uppsala group [105,98] (92 and 162 MeV, 109 data), and at Louvainla-Neuve [96] (84 data between 29 and 73 MeV). In table 10 we show the χ 2 /datum for the reproduction of these data sets by some recent PSA and NN potentials.…”