171 research outputs found
An analytical solver for the multi-group two-dimensional neutron-diffusion equation by integral transform techniques
In this work, we present an analytical solver for neutron diffusion in a rectangular two-dimensional geometry by a two-step integral transform procedure. To this end, we consider a regionwise homogeneous problem for two energy groups, i.e. fast and thermal neutrons, respectively. Each region has its specific physical properties, specified by cross-sections and diffusion constants. The problem is set
up by two coupled bi-dimensional diffusion equations in agreement with general perturbation theory. These are solved by integral transforms Laplace transform and generalized integral transform technique yielding analytical expressions for the scalar neutron fluxes. The solutions for neutron fluxes are presented for fast and
thermal neutrons in the four regions
On the Density Dependent Nuclear Matter Compressibility
In the present work we apply a quantum hadrodynamic effective model in the
mean-field approximation to the description of neutron stars. We consider an
adjustable derivative-coupling model and study the parameter influence on the
dynamics of the system by analyzing the full range of values they can take. We
establish a set of parameters which define a specific model that is able to
describe phenomenological properties such as the effective nucleon mass at
saturation as well as global static properties of neutron stars (mass and
radius). If one uses observational data to fix the maximum mass for neutron
stars by a specific model, we are able to predict the compression modulus of
nuclear matter K = 257,2MeV
Semiclassical dynamics of a spin-1/2 in an arbitrary magnetic field
The spin coherent state path integral describing the dynamics of a
spin-1/2-system in a magnetic field of arbitrary time-dependence is considered.
Defining the path integral as the limit of a Wiener regularized expression, the
semiclassical approximation leads to a continuous minimal action path with
jumps at the endpoints. The resulting semiclassical propagator is shown to
coincide with the exact quantum mechanical propagator. A non-linear
transformation of the angle variables allows for a determination of the
semiclassical path and the jumps without solving a boundary-value problem. The
semiclassical spin dynamics is thus readily amenable to numerical methods.Comment: 16 pages, submitted to Journal of Physics
Improved limits on nuebar emission from mu+ decay
We investigated mu+ decays at rest produced at the ISIS beam stop target.
Lepton flavor (LF) conservation has been tested by searching for \nueb via the
detection reaction p(\nueb,e+)n. No \nueb signal from LF violating mu+ decays
was identified. We extract upper limits of the branching ratio for the LF
violating decay mu+ -> e+ \nueb \nu compared to the Standard Model (SM) mu+ ->
e+ nue numub decay: BR < 0.9(1.7)x10^{-3} (90%CL) depending on the spectral
distribution of \nueb characterized by the Michel parameter rho=0.75 (0.0).
These results improve earlier limits by one order of magnitude and restrict
extensions of the SM in which \nueb emission from mu+ decay is allowed with
considerable strength. The decay \mupdeb as source for the \nueb signal
observed in the LSND experiment can be excluded.Comment: 10 pages, including 1 figure, 1 tabl
The inclusive 56Fe(nu_e,e-)56Co cross section
We study the 56Fe(nu_e,e^-)56Co cross section for the KARMEN neutrino
spectrum. The Gamow-Teller contribution to the cross section is calculated
within the shell model, while the forbidden transitions are evaluated within
the continuum random phase approximation. We find a total cross section of 2.73
x 10^-40 cm^2, in agreement with the data.Comment: 4 pages, 1 figure. Replaced due to new improved calculation
The Lie Algebraic Significance of Symmetric Informationally Complete Measurements
Examples of symmetric informationally complete positive operator valued
measures (SIC-POVMs) have been constructed in every dimension less than or
equal to 67. However, it remains an open question whether they exist in all
finite dimensions. A SIC-POVM is usually thought of as a highly symmetric
structure in quantum state space. However, its elements can equally well be
regarded as a basis for the Lie algebra gl(d,C). In this paper we examine the
resulting structure constants, which are calculated from the traces of the
triple products of the SIC-POVM elements and which, it turns out, characterize
the SIC-POVM up to unitary equivalence. We show that the structure constants
have numerous remarkable properties. In particular we show that the existence
of a SIC-POVM in dimension d is equivalent to the existence of a certain
structure in the adjoint representation of gl(d,C). We hope that transforming
the problem in this way, from a question about quantum state space to a
question about Lie algebras, may help to make the existence problem tractable.Comment: 56 page
Probing Sterile Neutrino Parameters with Double Chooz, Daya Bay and RENO
In this work, we present a realistic analysis of the potential of the
present-day reactor experiments Double Chooz, Daya Bay and RENO for probing the
existence of sterile neutrinos. We present exclusion regions for sterile
oscillation parameters for each of these experiments, using simulations with
realistic estimates of systematic errors and detector resolutions, and compare
the sterile parameter sensitivity regions we obtain with the existing bounds
from other reactor experiments. We find that these experimental set-ups give
significant bounds on the parameter \Theta_{ee} especially in the low sterile
oscillation region 0.01 < \Delta m_{41}^2 < 0.05 eV^2. These bounds can add to
our understanding of the sterile neutrino sector since there is still a tension
in the allowed regions from different experiments for sterile parameters.Comment: 12 pages, 5 figure
Evidence for nu_mu -> nu_e Oscillations from Pion Decay in Flight Neutrinos
A search for nu_mu -> nu_e oscillations has been conducted at the Los Alamos
Meson Physics Facility using nu_mu from pi^+ decay in flight. An excess in the
number of beam-related events from the C(nu_e,e^-)X inclusive reaction is
observed. The excess is too large to be explained by normal nu_e contamination
in the beam at a confidence level greater than 99%. If interpreted as an
oscillation signal, the observed oscillation probability of (2.6 +- 1.0 +- 0.5)
x 10^{-3} is consistent with the previously reported nu_mu_bar -> nu_e_bar
oscillation evidence from LSND.Comment: 70 pages (LaTeX), 32 figures (PostScript), submitted to Phys. Rev. C.
Additional information at http://nu1.lampf.lanl.gov/~lsn
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