Analysis of theAzzmeasurement innpscattering atT

Abstract

We analyze a recent experiment in which the spin-correlation parameter A, in np scattering at Tl b --67.5 MeV was measured. The I = 0 phase parameters can now be determined much more accurately in a single-energy analysis at 50 MeV. The value found for the S~-D& mixing parameter rq is in excellent agreement with modern potential-model predictions.PACS number(s): 21.30. +y, 13.75. Cs, 12.40. gq Recently, a measurement of the spin-correlation parameter A"in np scattering at 67 5 MeV was reported [1]. In that Letter the authors claimed that their determination of the Si Di m-ixing parameter si at 50 MeV is in disagreement with modern NN potentialmodel predictions. When true, this result would be very disturbing. Because we just finished a preliminary version of the Nijmegen 0 -350 MeV NN partial-wave analysis in which no strange behavior of the cq was found, we decided to have a better look at this experiment at 67.5 MeV. Here, we give a brief report of our results in which we refute the claim of the Basel group [1]: We find the c~mixing parameter to be in excellent agreement with modern potential predictions. A complete and detailed

Construction of high-qualityNNpotential models

“…This potential has been used in the Nijmegen analyses [9,10,11] to parametrize the np isovector lower partial waves (except the np 1 S 0 ). In our latest analysis [1] (PWA93) we refer to it as the Nijm92pp potential.…”

“…Because our analysis of the np data (and hence our careful scrutiny of the np data) has only recently been finished [1], we originally constructed an update (Nijm92pp) of the Nijm78 potential for the pp data only. This pp potential was used in our earlier preliminary np analyses [9,10,11] to parametrize the isovector partial waves. It has χ 2 /N pp = 1.4, which is not as good as the Nijmegen PWA93.…”

Nucleon-nucleon scattering observables from solitary boson exchange potential

“…6, measured by the Basel group [25]. In this context, Klomp, Stoks, and de Swart [26] argue that a potential which describes A zz at this energy does not allow a high 3 SD 1 mixing angle ǫ 1 at 50 MeV. Their own PWA, including the Basel data, yields ǫ 1 = 2.2 • ± 0.5…”

Shell-model calculations and realistic effective interactions

“…From the early 1990s on there has been much progress in the field of nuclear forces. In the first place, the NN phase shift analysis was greatly improved by the Nijmegen group [82,83,84,85]. They performed a multienergy partial-wave analysis of all NN scattering data below 350 MeV laboratory energy after rejection of a rather large number of data (about 900 and 300 for the np and pp data, respectively) on the basis of statistical criteria.…”