133 research outputs found
Role of deformation in the nonmesonic decay of light hypernuclei
We discuss the nonmesonic decay of deformed p-shell hypernuclei. The Nilsson
model with angular momentum projection is employed in order to take into
account the deformation effects. The nonmesonic decay rate and the intrinsic
asymmetry parameter decrease as a function of the deformation
parameter, while the ratio of the neutron- to proton-induced decay rates
increases. We find that the deformation effects change these observables by
about 10 % for Be from the spherical limit.Comment: RevTex, 17 pages, 3 ps figure
Recent results on the nonmesonic weak decay of hypernuclei within a one-meson-exchange model
We update our previous results for the nonmesonic decay of C
and He. We pay special attention to the role played by Final State
Intreractions on the decay observables. We follow a One-Meson-Exchange model
which includes the exchange of the and
mesons. We also present recent predictions for different observables concerning
the decay of the doubly strange He hypernucleus.Comment: 4 pages. Contribution to the Mesons and Light Nuclei'01 Conference,
Prague, 2-6 July 200
Lowest Order Effective Field Theory for the weak interaction
The interaction, responsible for the decay of
hypernuclei, is studied by means of an Effective Field Theory where the long
range physics is described by pion and kaon exchange mechanisms, and its short
range counterpart is obtained from the most general non-derivative local
four-fermion interaction. We show that, including the Lowest Order Parity
Conserving contact terms, allows us to reproduce the total decay rates for
, and with
a reasonable value of , while in order to get a prediction for
the Parity Violating (PV) asymmetry compatible with experiments, we have to
include the Lowest Order PV contact pieces.Comment: 3 pages, no figures. Contribution to the 17th International IUPAP
Conference on Few-body Problems in Physics, June 5-10, 2003 Durham, North
Carolina, USA. Uses espcrc1.st
Dynamical meson-baryon resonances with chiral Lagrangians
The s-wave meson-baryon interaction is studied using the lowest-order chiral
Lagrangian in a unitary coupled-channels Bethe-Salpeter equation. In the
strangeness sector the low-energy dynamics leads to the
dynamical generation of the as a state, along with
a good description of the scattering observables. At higher energies,
the is also found to be generated dynamically as a
quasibound state for the first time. For strangeness S=0, it is the
resonance that emerges from the coupled-channels equations,
leading to a satisfactory description of meson-baryon scattering observables in
the energy region around the . We speculate on the possible
dynamical generation of resonances within the chiral sector as
or quasibound states.Comment: 8 pages, 5 figures, Talk given at NSTAR2001, Workshop on the Physics
of Excited Nucleons, Mainz (Germany), March 7-10, to be published in World
Scientifi
Violation of the I=1/2 rule in the nonmesonic weak decay of hypernuclei
Violations of the I=1/2 rule are investigated in the nonmesonic weak
hypernuclear decay using a weak NNN transition potential based on
meson exchange. While the weak I=3/2 matrix elements of baryons with
pseudoscalar mesons are known to be very small, the same matrix elements of
baryons with vector mesons, evaluated in the factorization approximation, are
found to be significant. Within the uncertainties of the factorization
approximation we find that the total rate increases by at most 6% lying within
the error bars of the more recent experimental result. The neutron- to
proton-induced rate, on the other hand, can change by up to a factor of two,
while the asymmetry parameter is strongly affected as well.Comment: 17 pages. Paper related to a contribution presented at the
International Conference on Hypernuclear and Strange Particle Physics
(HYP97). Submitted to Phys. Lett.
Light nuclei and hypernuclei from quantum chromodynamics in the limit of SU(3) flavor symmetry
The binding energies of a range of nuclei and hypernuclei with atomic number A \u3c = 4 and strangeness vertical bar s vertical bar \u3c = 2, including the deuteron, dineutron, H - dibaryon, He - 3, He - 3 (Lambda), He - 4, He - 4(Lambda), and He - 4(Lambda Lambda), are calculated in the limit of flavor - SU (3) symmetry at the physical strange-quark mass with quantum chromodynamics (without electromagnetic interactions). The nuclear states are extracted from lattice QCD calculations performed with n (f) = 3 dynamical light quarks using an isotropic clover discretization of the quark action in three lattice volumes of spatial extent L similar to 3.4 fm, 4.5 fm, and 6.7 fm, and with a single lattice spacing b similar to 0.145 fm. DOI: 10.1103/PhysRevD.87.03450
Deuteron and exotic two-body bound states from lattice QCD
Results of a high-statistics, multivolume lattice QCD exploration of the deuteron, the dineutron, the H-dibaryon, and the Xi(-)Xi(-) system at a pion mass of m(pi) similar to 390 MeV are presented. Calculations were performed with an anisotropic n(f) = 2 + 1 clover discretization in four lattice volumes of spatial extent L similar to 2.0, 2.5, 2.9, and 3.9 fm, with a lattice spacing of b(s) similar to 0.123 fm in the spatial direction and b(t) similar to b(s)/3.5 in the time direction. Using the results obtained in the largest two volumes, the Xi(-)Xi(-) is found to be bound by B(Xi-Xi-)0 = 14.0(1.4)(6.7) MeV, consistent with expectations based upon phenomenological models and low-energy effective field theories constrained by nucleon-nucleon and hyperon-nucleon scattering data at the physical light-quark masses. Further, we find that the deuteron and the dineutron have binding energies of B-d = 11(05)(12) MeV and B-nn = 7.1(5.2)(7.3) MeV, respectively. With an increased number of measurements and a refined analysis, the binding energy of the H-dibaryon is B-H = 13.2(1.8)(4.0) MeV at this pion mass, updating our previous result
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