95 research outputs found
Geant4 Simulation of a filtered X-ray Source for Radiation Damage Studies
Geant4 low energy extensions have been used to simulate the X-ray spectra of
industrial X-ray tubes with filters for removing the uncertain low energy part
of the spectrum in a controlled way. The results are compared with precisely
measured X-ray spectra using a silicon drift detector. Furthermore, this paper
shows how the different dose rates in silicon and silicon dioxide layers of an
electronic device can be deduced from the simulations
The marine kd and water/sediment interaction problem
The behavior of marine distribution coefficients is analyzed with the help of numerical experiments and ana-lytical solutions of equations describing kinetic models
for uptake/release of radionuclides. The difficulties in measuring true kd in a marine environment perturbed by an external radionuclide source are highlighted.
Differences between suspended matter and bed sediment kd are analyzed. The performances of different kinetic models (1-step/2step; single-layer/multi-layer) are
studied in model/model and model/experiment compar-isons. Implications for the use of models to assess radioactive contamination after an emergency are given; as
well as recommendations when kd data are compiled in order to create a useful databaseInternational Atomic Energy Agency (IAEA) KIOST PE9961
First Observation of Radiative B^0 -> \phi K^0 \gamma Decays and Measurements of Their Time-Dependent CP Violation
We report the first observation of the radiative decay B^0 -> \phi K^0 \gamma
using a data sample of 772 x 10^6 B B-bar pairs collected at the \Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e^+e^-
collider. We observe a signal of 37+/-8 events with a significance of 5.4
standard deviations including systematic uncertainties. The measured branching
fraction is , where the uncertainties are statistical and systematic, respectively.
We also report the first measurements of time-dependent CP violation
parameters: and . Furthermore, we measure , and find that the signal is concentrated in
the M_{\phi K} mass region near threshold.Comment: 6 pages, 3 figures, Modified version is to be published in PRD(RC
Bounds on the width, mass difference and other properties of X(3872) --> pi+pi-J/psi decays
We present results from a study of X(3872) --> pi+pi- J/psi decays produced
via exclusive B--> K X(3872) decays. We determine the mass to be M_X(3872)=
(3871.84\pm 0.27 (stat)\pm 0.19 (syst)) MeV, a 90% CL upper limit on the
natural width of Gamma_X(3872)
K+X(3872))xBf(X(3872)-->pi+pi-J/psi)=(8.61 \pm 0.82(stat) \pm 0.52 (syst))
x10^{-6}, and a ratio of branching fractions Bf(B0--> K0 X(3872))/BF(B+--> K+
X(3872))=0.50\pm 0.14(stat)\pm0.04(syst). The difference in mass between the
X(3872)-->pi+pi-J/psi signals in B+ and B0 decays is Delta M_{X(3872)= (-0.69
\pm 0.97 (stat)} \pm 0.19 (syst)) MeV. A search for a charged partner of the
X(3872) in the decays Bbar0-->K- X+ or B+-->K0X+, X+-->pi+pi0 J/psi resulted in
upper limits on the product branching fractions for these processes that are
well below expectations for the case that the X(3872) is the neutral member of
an isospin triplet. In addition, we examine possible J^{PC} quantum number
assignments for the X(3872) based on comparisons of angular correlations
between final state particles in X(3872)-->pi+pi-J/psi decays with simulated
data for J^{PC} values of 1^{++} and 2^{-+}. We examine the influence of
rho-omega interference in the M(pi+pi-) spectrum. The analysis is based on a
711fb^{-1} data sample that contains 772 million BBbar meson pairs collected at
the Upsilon(4S) resonance in the Belle detector at the KEKB e+e- collider.Comment: 15 pages, 10 figures and 6 tables. Submitted to Physical Review
Measurements of Branching Fractions and Time-dependent CP Violating Asymmetries in Decays
We report measurements of branching fractions and time-dependent CP
asymmetries in and decays
using a data sample that contains pairs
collected at the resonance with the Belle detector at the KEKB
asymmetric-energy collider. We determine the branching fractions to
be
and . We measure CP asymmetry parameters and in and , ,
, and in , where the first uncertainty is
statistical and the second is systematic. We exclude the conservation of CP
symmetry in both decays at equal to or greater than significance.Comment: 7 pages, 2 figure
Ab initio van der Waals interactions in simulations of water alter structure from mainly tetrahedral to high-density-like
The structure of liquid water at ambient conditions is studied in ab initio
molecular dynamics simulations using van der Waals (vdW) density-functional
theory, i.e. using the new exchange-correlation functionals optPBE-vdW and
vdW-DF2. Inclusion of the more isotropic vdW interactions counteracts highly
directional hydrogen-bonds, which are enhanced by standard functionals. This
brings about a softening of the microscopic structure of water, as seen from
the broadening of angular distribution functions and, in particular, from the
much lower and broader first peak in the oxygen-oxygen pair-correlation
function (PCF), indicating loss of structure in the outer solvation shells. In
combination with softer non-local correlation terms, as in the new
parameterization of vdW-DF, inclusion of vdW interactions is shown to shift the
balance of resulting structures from open tetrahedral to more close-packed. The
resulting O-O PCF shows some resemblance with experiment for high-density water
(A. K. Soper and M. A. Ricci, Phys. Rev. Lett., 84:2881, 2000), but not
directly with experiment for ambient water. However, an O-O PCF consisting of a
linear combination of 70% from vdW-DF2 and 30% from experiment on low-density
liquid water reproduces near-quantitatively the experimental O-O PCF for
ambient water, indicating consistency with a two-liquid model with fluctuations
between high- and low-density regions
Observation of and Evidence for
We report the first observation of and first
evidence for , which are CP eigenstate decay modes.
These results are obtained from of data collected at
the resonance with the Belle detector at the KEKB
collider. We measure the branching fractions with a significance of , and
with a significance of . The last error
listed is due to uncertainty in the number of produced pairs.Comment: 5 pages, 2 figures, 2 tables, published in PR
First observation of CP violation and improved measurement of the branching fraction and polarization of B0 -> D*+ D*- decays
We report the measurement of the branching fraction, the polarization, and
the parameters of the time-dependent CP violation in B0 -> D*+ D*- decays using
a data sample of 772 million BB pairs, collected at the Y(4S) resonance with
the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain a
branching fraction of B = (7.82 +- 0.38 +- 0.63) x10^{-4}, a CP-odd fraction of
R_\perp = 0.138 +- 0.024 +- 0.006 and, additionally, a fraction of the
longitudinal component in the transversity base of R_0 = 0.624 +- 0.029 +-
0.011. The measured values of the parameters of the CP violation are S_{D*+
D*-} = -0.79 +- 0.13 +- 0.03 and A_{D*+ D*-} = 0.15 +- 0.08 +- 0.04
Search for Time-Dependent CPT Violation in Hadronic and Semileptonic B Decays
We report a new sensitive search for CPT violation, which includes improved
measurements of the CPT-violating parameter z and the total decay-width
difference normalized to the averaged width DeltaGamma_d/Gamma_d of the two Bd
mass eigenstates. The results are based on a data sample of 535 x 10^6 BBbar
pairs collected at the Upsilon(4S) resonance with the Belle detector at the
KEKB asymmetric-energy e^+e^- collider. We obtain Re(z) = [+1.9 +/- 3.7 (stat)
+/- 3.3 (syst)] x 10^{-2}, Im(z) = [-5.7 +/- 3.3 (stat) +/- 3.3 (syst)] x
10^{-3}, and DeltaGamma_d/Gamma_d = [-1.7 +/- 1.8 (stat) +/- 1.1 (syst)] x
10^{-2}, all of which are consistent with zero. This is the most precise single
measurement of these parameters in the neutral B-meson system to date.Comment: 7 pages, 3 figures, 2 tables, LaTeX; addition of supplemental
information, corrections of typos, results unchange
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