17 research outputs found
The Proton-Deuteron Break-Up Process in a Three-Dimensional Approach
The pd break-up amplitude in the Faddeev scheme is calculated by employing a
three-dimensional method without partial wave decomposition (PWD). In a first
step and in view of higher energies only the leading term is evaluated and this
for the process d(p,n)pp. A comparison with the results based on PWD reveals
discrepancies in the cross section around 200 MeV. This indicates the onset of
a limitation of the partial wave scheme. Also, around 200 MeV relativistic
effects are clearly visible and the use of relativistic kinematics shifts the
cross section peak to where the experimental peak is located. The theoretical
peak height, however, is wrong and calls first of all for the inclusion of
rescattering terms, which are shown to be important in a nonrelativistic full
Faddeev calculation in PWD.Comment: 4 pages, 5 figures, Proceeding of the Second Asia-Pasific Conference
on Few-Body Problem in Physics, August 2002, Shanghai, Chin
Calculation of the Two-body T-matrix in Configuration Space
A spectral integral method (IEM) for solving the two-body Schroedinger
equation in configuration space is generalized to the calculation of the
corresponding T-matrix. It is found that the desirable features of the IEM,
such as the economy of mesh-points for a given required accuracy, are carried
over also to the solution of the T-matrix. However the algorithm is
considerably more complex, because the T-matrix is a function of two variables
r and r', rather than only one variable r, and has a slope discontinuity at
r=r'. For a simple exponential potential an accuracy of 7 significant figures
is achieved, with the number N of Chebyshev support points in each partition
equal to 17. For a potential with a large repulsive core, such as the potential
between two He atoms, the accuracy decreases to 4 significant figures, but is
restored to 7 if N is increased to 65.Comment: 22 pages, 1 table 8 figure
Recent results in chiral nuclear dynamics
Some recent developments in the description of nuclear forces and few-nucleon
dynamics derived from chiral effective field theory are reviewed.Comment: invited talk at the International Workshop SCGT 02 "Strong Coupling
Gauge Theories and Effective Field Theories", 10-13 December 2002, Nagoya,
Japa
Chiral dynamics in few-nucleon systems
We employ the chiral nucleon-nucleon potential derived using the method of
unitary transformation up to next-to-next-to-leading order (NNLO) to study
bound and scattering states in the two-nucleon system. The predicted partial
wave phase shifts and mixing parameters for higher energies and higher angular
momenta beyond the ones which are fitted are mostly well described for energies
below 300 MeV. Various deuteron properties are discussed. We also apply the
next-to-leading order (NLO) potential to 3N and 4N systems. The resulting 3N
and 4N binding energies are in the same range what is found using standard NN
potentials. Experimental low-energy 3N scattering observables are also very
well reproduced like for standard NN forces. Surprisingly the long standing
Ay-puzzle is resolved at NLO. The cut-off dependence of the scattering
observables is rather mild.Comment: LaTeX2e, 8 pages; invited talk presented at the XVIIth European
Conference on Few-Body Problems in Physics, Evora, Portugal, September 2000;
to be published in the Proceeding
Chiral dynamics in few-nucleon systems
We report on recent progress achieved in calculating various few-nucleon
low-energy observables from effective field theory. Our discussion includes
scattering and bound states in the 2N, 3N and 4N systems and isospin violating
effects in the 2N system. We also establish a link between the nucleon-nucleon
potential derived in chiral effective field theory and various modern
high-precision potentials.Comment: 12 pp, uses aipproc style files, 4 figures, contribution to the
conference on "Mesons and Light Nuclei", Prag, July 2001, to appear in the
proceeding
A New Measurement of the 1S0 Neutron-Neutron Scattering Length using the Neutron-Proton Scattering Length as a Standard
The present paper reports high-accuracy cross-section data for the 2H(n,nnp)
reaction in the neutron-proton (np) and neutron-neutron (nn)
final-state-interaction (FSI) regions at an incident mean neutron energy of
13.0 MeV. These data were analyzed with rigorous three-nucleon calculations to
determine the 1S0 np and nn scattering lengths, a_np and a_nn. Our results are
a_nn = -18.7 +/- 0.6 fm and a_np = -23.5 +/- 0.8 fm. Since our value for a_np
obtained from neutron-deuteron (nd) breakup agrees with that from free np
scattering, we conclude that our investigation of the nn FSI done
simultaneously and under identical conditions gives the correct value for a_nn.
Our value for a_nn is in agreement with that obtained in pion-deuteron capture
measurements but disagrees with values obtained from earlier nd breakup
studies.Comment: 4 pages and 3 figure
A Model for the 3He(\vec d, p)4He Reaction at Intermediate Energies
Polarization correlation coefficients have been measured atRIKEN for the \vec
3He(\vec d,p)4He reaction at intermediate energies. We propose a model for the
(\vec d, p) reaction mechanism using the pd elastic scattering amplitude which
is rigorously determined by a Faddeev calculation and using modern NN forces.
Our theoretical predictions for deuteron polarization observables A_y, A_{yy},
A_{xx} and A_{xz} at E_d=140, 200 and 270 MeV agree qualitatively in shape with
the experimental data for the reaction 3He(\vec d,p)4He.Comment: 6 pages, 11 figures, 1 table, reference:
http://www.phys.ntu.edu.tw/english/fb16/contribution/topic4/Uesaka_Tomohiro1.
ps in Contribution for the XVIth IUPAP International Conference on Few-Body
Problems in Physics, (Taipei, Taiwan 6-11, March 2000
Resonance saturation for four-nucleon operators
In the modern description of nuclear forces based on chiral effective field
theory, four-nucleon operators with unknown coupling constants appear. These
couplings can be fixed by a fit to the low partial waves of neutron-proton
scattering. We show that the so determined numerical values can be understood
on the basis of phenomenological one-boson-exchange models. We also extract
these values from various modern high accuracy nucleon-nucleon potentials and
demonstrate their consistency and remarkable agreement with the values in the
chiral effective field theory approach. This paves the way for estimating the
low-energy constants of operators with more nucleon fields and/or external
probes.Comment: 16 pp, REVTeX, 3 figure