920 research outputs found
Structure of the vacuum states in the presence of isovector and isoscalar pairing correlations
The long standing problem of proton-neutron pairing and, in particular, the
limitations imposed on the solutions by the available symmetries, is revisited.
We look for solutions with non-vanishing expectation values of the proton, the
neutron and the isoscalar gaps. For an equal number of protons and neutrons we
find two solutions where the absolute values of proton and neutrons gaps are
equal but have the same or opposite sign. The behavior and structure of these
solutions differ for spin saturated (single l-shell) and spin unsaturared
systems (single j-shell). In the former case the BCS results are checked
against an exact calculation.Comment: 19 pages, 5 postscript figure
The Isovector Quadrupole-Quadrupole Interaction Used in Shell Model Calculations
An interaction is used
in a shell model calculation for . Whereas for the state
is two-fold degenerate, introducing a negative causes an `isovector'
state to come down to zero energy at and an triplet
() to come down to zero energy at . These are
undesirable properties, but a large negative is apparently needed to fit
the energy of the isovector giant quadrupole resonance.Comment: 12 pages, revtex, 2 figures (available on request
N* and Meson Resonances in J/psi decays
Over sixty million J/psi events have been collected by the BES Collaboration
at the Beijing Electron-Positron Collider (BEPC). J/psi decays provide an
excellent place for studying excited nucleons and hyperons -- N*, ,
and resonances, as well as meson resonances, including
possible glueballs and hybrids. Physics objectives, recent results and future
prospects of light hadron spectroscopy at BEPC are presented.Comment: Invited talk at the 7th International Workshop on Production,
Properties and Interaction of Mesons, Cracow, Poland, May 23-28, 200
The cranking formula and the spurious behaviour of the mass parameters
We discuss some aspects of the approach of the mass parameters by means of
the simple cranking model. In particular, it is well known that the numerical
application of this formula is often subject to ambiguities or contradictions.
It is found that these problems are induced by the presence of two derivatives
in the formula. To overcome these problems, we state a useful ansatz and we
develop a number of simple arguments which tend to justify the removal of these
terms. As soon as this is done, the formula becomes simpler and easier to
interpret. In this respect, it is shown how the shell effects affect the mass
parameters. A number of numerical tests help us in our conclusions.Comment: version 3 corrigendum of the ansatz of section V, corrigendum of the
legend of Fig3. Submission = text file + 5 figure
Measurement of B(D+ -> mu+ nu) and the pseudoscalar decay constant f_D at CLEO
The analysis of 60 1/pb data collected on the psi(3770) resonance with the
CLEO-c detector has produced the first statistically significant signal for D+
-> mu+ nu decay and led to the measurement of the decay branching fraction B(D+
-> mu+ nu) = (3.5 +- 1.4 +- 0.6) x 10-4 and the pseudoscalar decay constant f_D
= (202 +- 41 +- 17) MeV.Comment: Talk presented at the 1st Meeting of the APS Topical Group on
Hadronic Physics (Fermilab, Oct. 24-26, 2004). LaTeX 4 pages, 2 figure
Triaxial quadrupole deformation dynamics in sd-shell nuclei around 26Mg
Large-amplitude dynamics of axial and triaxial quadrupole deformation in
24,26Mg, 24Ne, and 28Si is investigated on the basis of the quadrupole
collective Hamiltonian constructed with use of the constrained
Hartree-Fock-Bogoliubov plus the local quasiparticle random phase approximation
method. The calculation reproduces well properties of the ground rotational
bands, and beta and gamma vibrations in 24Mg and 28Si. The gamma-softness in
the collective states of 26Mg and 24Ne are discussed. Contributions of the
neutrons and protons to the transition properties are also analyzed in
connection with the large-amplitude quadrupole dynamics.Comment: 16 pages, 18 figures, submitted to Phys. Rev.
Anomalous rotational-alignment in N=Z nuclei and residual neutron-proton interaction
Recent experiments have demonstrated that the rotational-alignment for the
nuclei in the mass-80 region is considerably delayed as compared to the
neighboring nuclei. We investigate whether this observation can be
understood by a known component of nuclear residual interactions. It is shown
that the quadrupole-pairing interaction, which explains many of the delays
known in rare-earth nuclei, does not produce the substantial delay observed for
these nuclei. However, the residual neutron-proton interaction which is
conjectured to be relevant for nuclei is shown to be quite important in
explaining the new experimental data.Comment: 4 pages, 3 figures, final version accepted by Phys. Rev. C as a Rapid
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