224,133 research outputs found
Observation of Bs->Ds(*)+Ds(*)- using e+e- collisions and a determination of the Bs-Bsbar width difference \Delta\Gamma_s
We have made the first observation of Bs->Ds(*)+Ds(*)- decays using 23.6 fb-1
of data recorded by the Belle experiment running on the Upsilon(5S) resonance.
The branching fractions are measured to be B(B^0_s\ra D^+_s D^-_s) =
(1.0\,^{+0.4}_{-0.3}\,^{+0.3}_{-0.2})%, B(B^0_s\ra D^{*\pm}_s D^{\mp}_s) =
(2.8\,^{+0.8}_{-0.7}\,\pm 0.7)%, and B(B^0_s\ra D^{*+}_s D^{*-}_s) =
(3.1\,^{+1.2}_{-1.0}\,\pm 0.8)%; the sum is B(B^0_s\ra D^{(*)+}_s D^{(*)-}_s) =
(6.9\,^{+1.5}_{-1.3}\,\pm 1.9)%. Assuming Bs->Ds(*)+Ds(*)- saturates decays to
CP-even final states, the branching fraction determines the ratio
\Delta\Gamma_s/cos(\phi), where \Delta\Gamma_s is the difference in widths
between the two Bs-Bsbar mass eigenstates, and \phi is a CP-violating weak
phase. Taking CP violation to be negligibly small, we obtain
\Delta\Gamma_s/\Gamma_s =
0.147^{+0.036}_{-0.030}(stat.)^{+0.044}_{-0.042}(syst.), where \Gamma_s is the
mean decay width.Comment: 13 pages, 2 figures, 2 tables. v2: text added for clarification,
version published in Phys. Rev. Letter
Anomalous spin Hall effects in Dresselhaus (110) quantum wells
Anomalous spin Hall effects that belong to the intrinsic type in Dresselhaus
(110) quantum wells are discussed. For the out-of-plane spin component,
antisymmetric current-induced spin polarization induces opposite spin Hall
accumulation, even though there is no spin-orbit force due to Dresselhaus (110)
coupling. A surprising feature of this spin Hall induction is that the spin
accumulation sign does not change upon bias reversal. Contribution to the spin
Hall accumulation from the spin Hall induction and the spin deviation due to
intrinsic spin-orbit force as well as extrinsic spin scattering, can be
straightforwardly distinguished simply by reversing the bias. For the inplane
component, inclusion of a weak Rashba coupling leads to a new type of
intrinsic spin Hall effect solely due to spin-orbit-force-driven spin
separation.Comment: 6 pages, 5 figure
Decoherence-free subspace and disentanglement dynamics for two qubits in a common non-Markovian squeezed reservoir
We study the non-Markovian entanglement dynamics of two qubits in a common
squeezed bath. We see remarkable difference between the non-Markovian
entanglement dynamics with its Markovian counterpart. We show that a
non-Markovian decoherence free state is also decoherence free in the Markovian
regime, but all the Markovian decoherence free states are not necessarily
decoherence free in the non-Markovian domain. We extend our calculation from
squeezed vacuum bath to squeezed thermal bath, where we see the effect of
finite bath temperatures on the entanglement dynamics.Comment: To appear in Phys. Rev. A (8 pages
B Decays as Spectroscope for Charmed Four-quark States
The state recently observed by BaBar in the channel
may be the first of a host of four-quark states. We give a
phenomenological account of the masses and decay modes. The isosinglet
state is the only narrow one, dominated by the observed isospin
violating decay and less than 100 keV in width. All other states are
expected to decay hadronically. Notable resonances are in doubly charged
, , wrong pairing , and also ,
channels. We propose B decays as searching ground for such 4-quark states,
which recoil against meson from B decay, or , mesons from decay. Exotic
charmonia could also be produced, and may be behind the slow bump in
inclusive decay.Comment: 6 pages and 2 figure
Sensitivities of Low Energy Reactor Neutrino Experiments
The low energy part of the reactor neutrino spectra has not been
experimentally measured. Its uncertainties limit the sensitivities in certain
reactor neutrino experiments. The origin of these uncertainties are discussed,
and the effects on measurements of neutrino interactions with electrons and
nuclei are studied. Comparisons are made with existing results. In particular,
the discrepancies between previous measurements with Standard Model
expectations can be explained by an under-estimation of the low energy reactor
neutrino spectra. To optimize the experimental sensitivities, measurements for
\nuebar-e cross-sections should focus on events with large (1.5 MeV)
recoil energy while those for neutrino magnetic moment searches should be based
on events 100 keV. The merits and attainable accuracies for
neutrino-electron scattering experiments using artificial neutrino sources are
discussed.Comment: 25 pages, 9 figure
Prediction of strong shock structure using the bimodal distribution function
A modified Mott-Smith method for predicting the one-dimensional shock wave
solution at very high Mach numbers is constructed by developing a system of
fluid dynamic equations. The predicted shock solutions in a gas of Maxwell
molecules, a hard sphere gas and in argon using the newly proposed formalism
are compared with the experimental data, direct-simulation Monte Carlo (DSMC)
solution and other solutions computed from some existing theories for Mach
numbers M<50. In the limit of an infinitely large Mach number, the predicted
shock profiles are also compared with the DSMC solution. The density,
temperature and heat flux profiles calculated at different Mach numbers have
been shown to have good agreement with the experimental and DSMC solutionsComment: 22 pages, 9 figures, Accepted for publication in Physical Review
Lattice QCD study of mixed systems of pions and kaons
The different ground state energies of N-pion and M-kaon systems for N+M <=12
are studied in lattice QCD. These energies are then used to extract the various
two- and three- body interactions that occur in these systems. Particular
attention is paid to additional thermal states present in the spectrum because
of the finite temporal extent. These calculations are performed using one
ensemble of 2+1 flavor anisotropic lattices with a spatial lattice spacing a_s
~ 0.125 fm, an anisotropy factor {\xi}=a_s/a_t=3.5, and a spatial volume L^3 ~
(2.5 fm)^3. The quark masses used correspond to pion and kaon masses of m_{\pi}
~ 383 MeV and m_K ~ 537 MeV, respectively. The isospin and strangeness chemical
potentials of these systems are found to be in the region where chiral
perturbation theory and hadronic models predict a phase transition between a
pion condensed phase and a kaon condensed phase
Testing Strict Hydrostatic Equilibrium in Simulated Clusters of Galaxies: Implications to Abell 1689
Accurate mass determination of clusters of galaxies is crucial if they are to
be used as cosmological probes. However, there are some discrepancies between
cluster masses determined based on gravitational lensing, and X-ray
observations assuming strict hydrostatic equilibirium (i.e., the equilibrium
gas pressure is provided entirely by thermal pressure). Cosmological
simulations suggest that turbulent gas motions remaining from hierarchical
structure formation may provide a significant contribution to the equilibrium
pressure in clusters. We analyze a sample of massive clusters of galaxies drawn
from high resolution cosmological simulations, and find a significant
contribution (20%-45%) from non-thermal pressure near the center of relaxed
clusters, and, in accord with previous studies, a minimum contribution at about
0.1 Rvir, growing to about 30%-45% at the virial radius, Rvir. Our results
strongly suggest that relaxed clusters should have significant non-thermal
support in their core region. As an example, we test the validity of strict
hydrostatic equilibirium in the well-studied massive galaxy cluster Abell 1689
using the latest high resolution gravitational lensing and X-ray observations.
We find a contribution of about 40% from non-thermal pressure within the core
region of A1689, suggesting an alternate explanation for the mass discrepancy:
the strict hydrostatic equilibirium is not valid in this region.Comment: Accepted for publication in The Astrophysical Journal Letters; 4
pages, 3 figure
Orbital-Free Density Functional Theory: Kinetic Potentials and Ab-Initio Local Pseudopotentials
In the density functional (DF) theory of Kohn and Sham, the kinetic energy of
the ground state of a system of noninteracting electrons in a general external
field is calculated using a set of orbitals. Orbital free methods attempt to
calculate this directly from the electron density by approximating the
universal but unknown kinetic energy density functional. However simple local
approximations are inaccurate and it has proved very difficult to devise
generally accurate nonlocal approximations. We focus instead on the kinetic
potential, the functional derivative of the kinetic energy DF, which appears in
the Euler equation for the electron density. We argue that the kinetic
potential is more local and more amenable to simple physically motivated
approximations in many relevant cases, and describe two pathways by which the
value of the kinetic energy can be efficiently calculated. We propose two
nonlocal orbital free kinetic potentials that reduce to known exact forms for
both slowly varying and rapidly varying perturbations and also reproduce exact
results for the linear response of the density of the homogeneous system to
small perturbations. A simple and systematic approach for generating accurate
and weak ab-initio local pseudopotentials which produce a smooth slowly varying
valence component of the electron density is proposed for use in orbital free
DF calculations of molecules and solids. The use of these local
pseudopotentials further minimizes the possible errors from the kinetic
potentials. Our theory yields results for the total energies and ionization
energies of atoms, and for the shell structure in the atomic radial density
profiles that are in very good agreement with calculations using the full
Kohn-Sham theory.Comment: To be published in Phys. Rev.
Beauty mesons in lattice QCD with exact chiral symmetry
We present the first study of treating b, c, and s quarks as Dirac fermions
in lattice QCD with exact chiral symmetry. For 100 gauge configurations
generated with single-plaquette action at beta = 7.2 on the 32^3 x 60 lattice,
we compute point-to-point quark propagators for 33 quark masses in the range
0.01 < m_q a < 0.85, and measure the time-correlation function of
(pseudo-)scalar, (pseudo-)vector, and tensor mesons, for symmetric and
asymmetric quark masses respectively. The lowest-lying mass spectra of mesons
with quark contents b_bbar, c_bbar, s_bbar, and c_cbar are determined, together
with the pseudoscalar decay constants. Our results are sumarized in Tables 1-5.
Furthermore, we also determine the b and c quark masses in the MS_bar scheme,
m_b = 4.65(5) GeV, and m_c = 1.16(4) GeV.Comment: 12 page
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