173 research outputs found
Threshold scattering of the eta-meson off light nuclei
The scattering lengths of eta-meson collisions with light nuclei d,t,3He, and
4He are calculated on the basis of few-body equations in coherent
approximation. It is found that the eta-nucleus scattering length depends
strongly on the number of nucleons and the potential-range parameter. By taking
into account the off-shell behavior of the eta-N amplitude, the eta-4He
scattering length increases considerably.Comment: 8 pages, no figures, RevTeX, submitted to Phys.Lett.
Isovector soft dipole mode in 6Be
By using the 1H(6Li,6Be)n charge-exchange reaction, continuum states in 6Be
were populated up to E_t=16 MeV, E_t being the 6Be energy above its three-body
decay threshold. In kinematically complete measurements performed by detecting
alpha+p+p coincidences, an E_t spectrum of high statistics was obtained,
containing approximately ~5x10^6 events. The spectrum provides detailed
correlation information about the well-known 0^+ ground state of 6Be at
E_t=1.37 MeV and its 2^+ state at E_t=3.05 MeV. Moreover, a broad structure
extending from 4 to 16 MeV was observed. It contains negative parity states
populated by Delta L=1 angular momentum transfer without other significant
contributions. This structure can be interpreted as a novel phenomenon, i.e.
the isovector soft dipole mode associated with the 6Li ground state. The
population of this mode in the charge-exchange reaction is a dominant
phenomenon for this reaction, being responsible for about 60% of the cross
section obtained in the measured energy range.Comment: 8 pages, 7 figure
Transition from BCS pairing to Bose-Einstein condensation in low-density asymmetric nuclear matter
We study the isospin-singlet neutron-proton pairing in bulk nuclear matter as
a function of density and isospin asymmetry within the BCS formalism. In the
high-density, weak-coupling regime the neutron-proton paired state is strongly
suppressed by a minor neutron excess. As the system is diluted, the BCS state
with large, overlapping Cooper pairs evolves smoothly into a Bose-Einstein
condensate of tightly bound neutron-proton pairs (deuterons). In the resulting
low-density system a neutron excess is ineffective in quenching the pair
correlations because of the large spatial separation of the deuterons and
neutrons. As a result, the Bose-Einstein condensation of deuterons is weakly
affected by an additional gas of free neutrons even at very large asymmetries.Comment: 17 pages, uncluding 7 figures, PRC in pres
Resonances in the three-neutron system
A study of 3-body resonances has been performed in the framework of
configuration space Faddeev equations. The importance of keeping a sufficient
number of terms in the asymptotic expansion of the resonance wave function is
pointed out. We investigated three neutrons interacting in selected force
components taken from realistic nn forces.Comment: 38 pages, 11 tables, 4 figure
- …