246 research outputs found
Two-phonon 1- state in 112Sn observed in resonant photon scattering
Results of a photon scattering experiment on 112Sn using bremsstrahlung with
an endpoint energy of E_0 = 3.8 MeV are reported. A J = 1 state at E_x =
3434(1) keV has been excited. Its decay width into the ground state amounts to
Gamma_0 = 151(17) meV, making it a candidate for a [2+ x 3-]1- two-phonon
state. The results for 112Sn are compared with quasiparticle-phonon model
calculations as well as the systematics of the lowest-lying 1- states
established in other even-mass tin isotopes. Contrary to findings in the
heavier stable even-mass Sn isotopes, no 2+ states between 2 and 3.5 MeV
excitation energy have been detected in the present experiment.Comment: 10 pages, including 2 figures, Phys. Rev. C, in pres
Modeling core collapse supernovae in 2 and 3 dimensions with spectral neutrino transport
The overwhelming evidence that the core collapse supernova mechanism is
inherently multidimensional, the complexity of the physical processes involved,
and the increasing evidence from simulations that the explosion is marginal
presents great computational challenges for the realistic modeling of this
event, particularly in 3 spatial dimensions. We have developed a code which is
scalable to computations in 3 dimensions which couples PPM Lagrangian with
remap hydrodynamics [1], multigroup, flux-limited diffusion neutrino transport
[2], with many improvements), and a nuclear network [3]. The neutrino transport
is performed in a ray-by-ray plus approximation wherein all the lateral effects
of neutrinos are included (e.g., pressure, velocity corrections, advection)
except the transport. A moving radial grid option permits the evolution to be
carried out from initial core collapse with only modest demands on the number
of radial zones. The inner part of the core is evolved after collapse along
with the rest of the core and mantle by subcycling the lateral evolution near
the center as demanded by the small Courant times. We present results of 2-D
simulations of a symmetric and an asymmetric collapse of both a 15 and an 11 M
progenitor. In each of these simulations we have discovered that once the
oxygen rich material reaches the shock there is a synergistic interplay between
the reduced ram pressure, the energy released by the burning of the shock
heated oxygen rich material, and the neutrino energy deposition which leads to
a revival of the shock and an explosion.Comment: 10 pages, 3 figure
Triangular mass matrices of quarks and Cabibbo-Kobayashi-Maskawa mixing
Every nonsingular fermion mass matrix, by an appropriate unitary
transformation of right-chiral fields, is equivalent to a triangular matrix.
Using the freedom in choosing bases of right-chiral fields in the minimal
standard model, reduction to triangular form reduces the well-known ambiguities
in reconstructing a mass matrix to trivial phase redefinitions. Furthermore,
diagonalization of the quark mass sectors can be shifted to one charge sector
only, without loosing the concise and economic triangular form. The
corresponding effective triangular mass matrix is reconstructed, up to trivial
phases, from the moduli of the CKM matrix elements, and vice versa, in a unique
way. A new formula for the parametrization independent CP-measure in terms of
observables is derived and discussed.Comment: 13 pages, Late
The Interaction of Quantum Gravity with Matter
The interaction of (linearized) gravitation with matter is studied in the
causal approach up to the second order of perturbation theory. We consider the
generic case and prove that gravitation is universal in the sense that the
existence of the interaction with gravitation does not put new constraints on
the Lagrangian for lower spin fields. We use the formalism of quantum off-shell
fields which makes our computation more straightforward and simpler.Comment: 25 page
Damping of supernova neutrino transitions in stochastic shock-wave density profiles
Supernova neutrino flavor transitions during the shock wave propagation are
known to encode relevant information not only about the matter density profile
but also about unknown neutrino properties, such as the mass hierarchy (normal
or inverted) and the mixing angle theta_13. While previous studies have
focussed on "deterministic" density profiles, we investigate the effect of
possible stochastic matter density fluctuations in the wake of supernova shock
waves. In particular, we study the impact of small-scale fluctuations on the
electron (anti)neutrino survival probability, and on the observable spectra of
inverse-beta-decay events in future water-Cherenkov detectors. We find that
such fluctuations, even with relatively small amplitudes, can have significant
damping effects on the flavor transition pattern, and can partly erase the
shock-wave imprint on the observable time spectra, especially for
sin^2(theta_13) > O(10^-3).Comment: v2 (23 pages, including 6 eps figures). Typos removed, references
updated, matches the published versio
Model-independent determination of the dipole response of <sup>66</sup>Zn using quasimonoenergetic and linearly polarized photon beams
Background: Photon strength functions are an important ingredient in calculations relevant for the nucleosynthesis of heavy elements. The relation to the photoabsorption cross section allows to experimentally constrain photon strength functions by investigating the photoresponse of atomic nuclei. Purpose: We determine the photoresponse of 66Zn in the energy region of 5.6 MeV to 9.9 MeV and analyze the contribution of the 'elastic' decay channel back to the ground state. In addition, for the elastic channel electric and magnetic dipole transitions were separated. Methods: Nuclear resonance fluorescence experiments were performed using a linearly polarized quasi-monoenergetic photon beam at the High Intensity gamma -ray Source. Photon beam energies from 5.6 to 9.9 MeV with an energy spread of about 3% were selected in steps of 200-300 keV. Two high purity germanium detectors were used for the subsequent gamma -ray spectroscopy. Results: Full photoabsorption cross sections are extracted from the data making use of the monoenergetic character of the photon beam. For the ground-state decay channel, the average contribution of electric and magnetic dipole strengths is disentangled. The average Conclusions: The new results indicate lower cross sections when compared to the values extracted from a former experiment using bremsstrahlung on 66Zn. In the latter, the average branching ratio to the ground state is estimated from statistical-model calculations in order to analyze the data. Corresponding estimates from statistical-model calculations underestimate this branching ratio compared to the values extracted from the present analysis, which would partly explain the high cross sections determined from the bremsstrahlung data
Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars
In this paper, the second of a series, we study the stellar dynamical and
evolutionary processes leading to the formation of compact binaries containing
neutron stars (NSs) in dense globular clusters (GCs). For this study, 70 dense
clusters were simulated independently, with a total stellar mass ~2x10^7Msun,
exceeding the total mass of all dense GCs in our Galaxy.
We find that, in order to reproduce the empirically derived formation rate of
low-mass X-ray binaries (LMXBs), we must assume that NSs can be formed via
electron-capture supernovae (ECS) with typical natal kicks smaller than in
core-collapse supernovae. Our results explain the observed dependence of the
number of LMXBs on ``collision number'' as well as the large scatter observed
between different GCs. We predict that the number of quiescent LMXBs in
different GCs should not have a strong metallicity dependence. In our cluster
model the following mass-gaining events create populations of MSPs that do not
match the observations: (i) accretion during a common envelope event with a NS
formed through ECS, and (ii) mass transfer (MT) from a WD donor. Some processes
lead only to a mild recycling. In addition, for MSPs, we distinguish
low-magnetic-field (long-lived) and high-magnetic-field (short-lived)
populations. With this distinction and by considering only those mass-gaining
events that appear to lead to NS recycling, we obtain good agreement of our
models with the numbers and characteristics of observed MSPs in 47 Tuc and
Terzan 5, as well as with the cumulative statistics for MSPs detected in GCs of
different dynamical properties. We find that significant production of merging
double NSs potentially detectable as short gamma-ray bursts occurs only in very
dense, most likely core-collapsed GCs. (abridged)Comment: 25 pages, 7 figures, 12 tables, MNRAS accepte
Electric quadrupole moments of the 2 states in Cd
Using the REX-ISOLDE facility at CERN the Coulomb excitation cross sections for the 0gs+â21+ transition in the ÎČ-unstable isotopes 100,102,104Cd have been measured for the first time. Two different targets were used, which allows for the first extraction of the static electric quadrupole moments Q(21+) in 102,104Cd. In addition to the B(E2) values in 102,104Cd, a first experimental limit for the B(E2) value in 100Cd is presented. The data was analyzed using the maximum likelihood method. The provided probability distributions impose a test for theoretical predictions of the static and dynamic moments. The data are interpreted within the shell-model using realistic matrix elements obtained from a G-matrix renormalized CD-Bonn interaction. In view of recent results for the light Sn isotopes the data are discussed in the context of a renormalization of the neutron effective charge. This study is the first to use the reorientation effect for post-accelerated short-lived radioactive isotopes to simultaneously determine the B(E2) and the Q(21+) values
Low-lying dipole response of 64Ni
Two complementary real-photon scattering experiments were conducted on the proton-magic 64 Ni nucleus to study the dipole response up to its neutron-separation energy of S n = 9.7 MeV . By combining both measurements, 87 E 1 and 23 M 1 transitions were identified above 4.3 MeV. The results of the observed M 1 transitions were compared to shell-model calculations using two different model spaces. It was found that the inclusion of excitations across the Z = 28 shell gap in the calculations has a large impact. Furthermore, average cross sections for decays to the ground state (elastic transitions) as well as to lower-lying excited states (inelastic decays) were determined. The corresponding E 1 channel was compared to calculations within the relativistic equation of motion (REOM) framework. Whereas the calculations of highest possible complexity reproduce the fragmentation and overall behavior of the E 1 average elastic cross section well, the predicted absolute cross sections are approximately twice as high as the experimental upper limits even though the latter also include an estimate of the inelastic-decay channel
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