7,119 research outputs found
Use of cumulants to quantify uncertainties in the HBT measurements of the homogeneity regions
Let us denote p(x|K) the space density of the points where identical
particles of some kind, e.g. pi+ mesons, with momentum K are produced. When
using the HBT method to determine p(x|K) one encounters ambiguities. We show
that these ambiguities do not affect the even cumulants of the distribution
p(x|K). In particular, the HBT radii of the homogeneity regions, which are
given by the second order cumulants, and the distribution of distances between
the pairs of production points for particles with momentum K can be reliably
measured. The odd cumulants are ambiguous. The are, however, correlated. In
particular, when the average position (K) is known as a function of K there
is no further ambiguity.Comment: LateX, 10 pages, no figure
High-spin intruder states in the fp shell nuclei and isoscalar proton-neutron correlations
We perform a systematic shell-model and mean-field study of fully-aligned,
high-spin f_{7/2}^{n} seniority isomers and d_{3/2}^{-1} f_{7/2}^{n+1} intruder
states in the A~44 nuclei from the lower-fp shell. The shell-model calculations
are performed in the full sdfp configuration space allowing 1p-1h cross-shell
excitations. The self-consistent mean-field calculations are based on the
Hartree-Fock approach with the Skyrme energy density functional that reproduces
empirical Landau parameters. While there is a nice agreement between
experimental and theoretical relative energies of fully-aligned states in N>Z
nuclei, this is no longer the case for the N=Z systems. The remaining deviation
from the data is attributed to the isoscalar proton-neutron correlations. It is
also demonstrated that the Coulomb corrections at high spins noticeably depend
on the choice of the energy density functional.Comment: 4 pages. submitted to Phys. Rev. Let
Surface-peaked effective mass in the nuclear energy density functional and its influence on single-particle spectra
Calculations for infinite nuclear matter with realistic nucleon-nucleon
interactions suggest that the isoscalar effective mass of a nucleon at the
saturation density, m*/m, equals 0.8 +/- 0.1. This result is at variance with
empirical data on the level density in finite nuclei, which are consistent with
m*/m ~ 1. Ma and Wambach suggested that these two contradicting results may be
reconciled within a single theoretical framework by assuming a radial-dependent
effective mass, peaked at the nuclear surface. The aim of this exploratory work
is to investigate this idea within the density functional theory by using a
Skyrme-type local functional enriched with new terms, and , where and
denote the kinetic and particle densities, respectively. We show that each of
these terms can give rise to a surface peak in the effective mass, but of a
limited height. We investigate the influence of the radial profile of the
effective mass on the spin-orbit splittings and centroids. In particular, we
demonstrate that the term quenches the 1f5/2-1f7/2
splitting in 40Ca, which is strongly overestimated within conventional Skyrme
parametrizations.Comment: 8 pages, 8 figures, submitted to Phys. Rev.
Spin-orbit and tensor mean-field effects on spin-orbit splitting including self-consistent core polarizations
A new strategy of fitting the coupling constants of the nuclear energy
density functional is proposed, which shifts attention from ground-state bulk
to single-particle properties. The latter are analyzed in terms of the bare
single-particle energies and mass, shape, and spin core-polarization effects.
Fit of the isoscalar spin-orbit and both isoscalar and isovector tensor
coupling constants directly to the f5/2-f7/2 spin-orbit splittings in 40Ca,
56Ni, and 48Ca is proposed as a practical realization of this new programme. It
is shown that this fit requires drastic changes in the isoscalar spin-orbit
strength and the tensor coupling constants as compared to the commonly accepted
values but it considerably and systematically improves basic single-particle
properties including spin-orbit splittings and magic-gap energies. Impact of
these changes on nuclear binding energies is also discussed.Comment: 15 pages, 7 figures, submitted to Physical Review
The effect of argon ion bombardment on the adhesion of gold and aluminum
Ion bombardment was studied as an effective means of cleaning metal surfaces and removing contaminant layers. This cleaning allowed aluminmum couples and gold couples to form bonds in thirty to sixty minutes without raising the temperature of the adhesion zone about 200 C In comparison tests conducted without ion bombardment cleaning, temperatures of 350 C, contact forces of 150 grams and exposure times of 172 hours were necessary to achieve a similar bond, in vacuum
The Renyi entropy H_2 as a rigorous, measurable lower bound for the entropy of the interaction region in multiparticle production processes
A model-independent lower bound on the entropy S of the multiparticle system
produced in high energy collisions, provided by the Renyi entropy H_2, is shown
to be very effective. Estimates show that the ratio H_2/S remains close to one
half for all realistic values of the parameters.Comment: Eur. Phys. J. C in print, 17 pages, 5 figure
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