Biomedical subjects

H Witala

Publications and source records attributed to H Witala.

At least 19 recordsLinked to original sources

PubMed2001

Three- and four-nucleon systems from chiral effective field theory.

Recently developed chiral nucleon-nucleon (NN) forces at next-to-leading order (NLO), that describe NN phase shifts up to about 100 MeV fairly well, have been applied to 3N and 4N systems. Faddeev-Yakubovsky equations have been solved rigorously. The resulting 3N and 4N binding energies are in the same range as found using standard NN potentials. In addition, low-energy 3N scattering observables are very well reproduced as for standard NN forces. The long-standing A(y) puzzle is absent at NLO. The cutoff dependence of the scattering observables is rather weak.

Journal Article↗

PubMed2000

New attempt to determine the n-n scattering length with the 2H(n, np)n reaction

The n-n final-state interaction (FSI) was investigated via the 2H(n, np)n reaction at 25 MeV, using a geometry which enables the simultaneous observation of n-p quasifree (QFS) scattering. The data were analyzed with Monte Carlo simulations based on rigorous Faddeev calculations with realistic nucleon-nucleon potentials. The value of a(nn) deduced from the absolute yield in the FSI peak is -16.27+/-0. 40 fm while the relative data, normalized in the QFS region, give -16.06+/-0.35 fm. Thus our results differ from the "recommended" value of a(nn) = -18.5+/-0.3 fm by more than 5 standard deviations.

Journal Article↗

PubMed2000

Precise measurement of dp elastic scattering at 270 MeV and three-nucleon force effects

The cross section, the deuteron vector A(d)(y) and tensor analyzing powers A(ij), the polarization transfer coefficients K(y('))(ij), and the induced polarization P(y(')) were measured for the dp elastic scattering at 270 MeV. The cross section and A(d)(y) are well reproduced by Faddeev calculations with modern data-equivalent nucleon-nucleon forces plus the Tucson-Melbourne three-nucleon force. In contrast, A(ij), K(y('))(ij), or P(y(')) are not described by such calculations. These facts indicate the deficiencies in the spin dependence of the Tucson-Melbourne force and call for extended three-nucleon force models.

Journal Article↗

PubMed2000

Three-nucleon force and the A(y) puzzle in intermediate energy p--> + d and d--> + p elastic scattering

New vector analyzing-power data on p-->+d elastic scattering at E(p) = 150 and 190 MeV have been measured. These are presented together with existing data and with recent d-->+p vector and tensor analyzing power data at E(d) = 270 MeV. The strong negative extremum of both vector analyzing powers A(p)(y) and A(d)(y) at straight theta(c.m.) approximately 80 degrees -120 degrees is underestimated by Faddeev calculations using modern NN forces. Inclusion of the Tucson-Melbourne 3N force shifts the minima upwards, but with conflicting results for A(p)(y), and leading to a good description for A(d)(y). An A(p)(y) puzzle, previously thought to exist at energies E(N)</=30 MeV only, appears to exist also at intermediate energies.

Journal Article↗

PubMed1996