862 research outputs found
Hadronic production of the -wave excited -states ()
Adopting the complete approach of the perturbative QCD (pQCD)
and updated parton distribution functions, we have estimated the hadronic
production of -wave excited -states (). In the estimate,
special care on the relation of the production amplitude to the derivative of
wave function at origin of the potential model is payed. For experimental
references, main uncertainties are discussed, and the total cross sections and
the distributions of the production with reasonable cuts at the energies of
Tevatron and LHC are computed and presented. The results show that -wave
production may contribute to the -meson production indirectly by a factor
about 0.5 of the direct production, and with such a big cross section, it is
worth further to study the possibility to observe the -wave production
itself experimentally.Comment: 23 pages, 9 figures, to replace for revising the misprints ec
The meson annihilation to leptons and inclusive light hadrons
The annihilation of the meson to leptons and inclusive light hadrons is
analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find
that the decay mode, which escapes from the helicity suppression, contributes a
sizable fraction width. According to the analysis, the branching ratio due to
the contribution from the color-singlet component of the meson can be of
order (10^{-2}). We also estimate the contributions from the color-octet
components. With the velocity scaling rule of NRQCD, we find that the
color-octet contributions are sizable too, especially, in certain phase space
of the annihilation they are greater than (or comparative to) the color-singlet
component. A few observables relevant to the spectrum of charged lepton are
suggested, that may be used as measurements on the color-octet and
color-singlet components in the future experiments. A typical long
distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.
Molecular orbital calculations of two-electron states for P donor solid-state spin qubits
We theoretically study the Hilbert space structure of two neighbouring P
donor electrons in silicon-based quantum computer architectures. To use
electron spins as qubits, a crucial condition is the isolation of the electron
spins from their environment, including the electronic orbital degrees of
freedom. We provide detailed electronic structure calculations of both the
single donor electron wave function and the two-electron pair wave function. We
adopted a molecular orbital method for the two-electron problem, forming a
basis with the calculated single donor electron orbitals. Our two-electron
basis contains many singlet and triplet orbital excited states, in addition to
the two simple ground state singlet and triplet orbitals usually used in the
Heitler-London approximation to describe the two-electron donor pair wave
function. We determined the excitation spectrum of the two-donor system, and
study its dependence on strain, lattice position and inter donor separation.
This allows us to determine how isolated the ground state singlet and triplet
orbitals are from the rest of the excited state Hilbert space. In addition to
calculating the energy spectrum, we are also able to evaluate the exchange
coupling between the two donor electrons, and the double occupancy probability
that both electrons will reside on the same P donor. These two quantities are
very important for logical operations in solid-state quantum computing devices,
as a large exchange coupling achieves faster gating times, whilst the magnitude
of the double occupancy probability can affect the error rate.Comment: 15 pages (2-column
Anharmonic effects on a phonon number measurement of a quantum mesoscopic mechanical oscillator
We generalize a proposal for detecting single phonon transitions in a single
nanoelectromechanical system (NEMS) to include the intrinsic anharmonicity of
each mechanical oscillator. In this scheme two NEMS oscillators are coupled via
a term quadratic in the amplitude of oscillation for each oscillator. One NEMS
oscillator is driven and strongly damped and becomes a transducer for phonon
number in the other measured oscillator. We derive the conditions for this
measurement scheme to be quantum limited and find a condition on the size of
the anharmonicity. We also derive the relation between the phase diffusion
back-action noise due to number measurement and the localization time for the
measured system to enter a phonon number eigenstate. We relate both these time
scales to the strength of the measured signal, which is an induced current
proportional to the position of the readout oscillator.Comment: 13 pages, 2 figure
Non-Markovian entanglement dynamics of quantum continuous variable systems in thermal environments
We study two continuous variable systems (or two harmonic oscillators) and
investigate their entanglement evolution under the influence of non-Markovian
thermal environments. The continuous variable systems could be two modes of
electromagnetic fields or two nanomechanical oscillators in the quantum domain.
We use quantum open system method to derive the non-Markovian master equations
of the reduced density matrix for two different but related models of the
continuous variable systems. The two models both consist of two interacting
harmonic oscillators. In model A, each of the two oscillators is coupled to its
own independent thermal reservoir, while in model B the two oscillators are
coupled to a common reservoir. To quantify the degrees of entanglement for the
bipartite continuous variable systems in Gaussian states, logarithmic
negativity is used. We find that the dynamics of the quantum entanglement is
sensitive to the initial states, the oscillator-oscillator interaction, the
oscillator-environment interaction and the coupling to a common bath or to
different, independent baths.Comment: 10 two-column pages, 8 figures, to appear in Phys. Rev.
Thermally-induced expansion in the 8 GeV/c + Au reaction
Fragment kinetic energy spectra for reactions induced by 8.0 GeV/c
beams incident on a Au target have been analyzed in
order to deduce the possible existence and influence of thermal expansion. The
average fragment kinetic energies are observed to increase systematically with
fragment charge but are nearly independent of excitation energy. Comparison of
the data with statistical multifragmentation models indicates the onset of
extra collective thermal expansion near an excitation energy of E*/A
5 MeV. However, this effect is weak relative to the radial
expansion observed in heavy-ion-induced reactions, consistent with the
interpretation that the latter expansion may be driven primarily by dynamical
effects such as compression/decompression.Comment: 12 pages including 4 postscript figure
Influence of an external magnetic field on the decoherence of a central spin coupled to an antiferromagnetic environment
Using the spin wave approximation, we study the decoherence dynamics of a
central spin coupled to an antiferromagnetic environment under the application
of an external global magnetic field. The external magnetic field affects the
decoherence process through its effect on the antiferromagnetic environment. It
is shown explicitly that the decoherence factor which displays a Gaussian decay
with time depends on the strength of the external magnetic field and the
crystal anisotropy field in the antiferromagnetic environment. When the values
of the external magnetic field is increased to the critical field point at
which the spin-flop transition (a first-order quantum phase transition) happens
in the antiferromagnetic environment, the decoherence of the central spin
reaches its highest point. This result is consistent with several recent
quantum phase transition witness studies. The influences of the environmental
temperature on the decoherence behavior of the central spin are also
investigated.Comment: 29 preprint pages, 4 figures, to appear in New Journal of Physic
The Population Migration in Taiwan, and its Causal Relationship with Labor Market and Housing Market
[[abstract]]This study sets out to empirically examine the interrelationship existing between the labor market, the housing market and domestic interregional migration in Taiwan, with four of the most urbanized population receiving areas, Taipei City, Taipei County, Taichung City and Kaohsiung City, being selected for the study. An error correction model is constructed for each city/county using time series data covering the period from 1974 to 1999, from which the research results show that each city/county has its own unique relational pattern between population migration, the labor market and the housing market, reflecting their different characteristics and developmental stages. In Taipei City, the capital city of Taiwan, housing prices are much higher, although this has not been affected by migration or the labor market, since it is instead exogenously determined. In Taipei County, on the other hand, which is part of the Taipei metropolitan area and the major population migration destination, a close interaction exists between housing prices and population migration. As a latecomer in urban development, the relatively better organized city planning in Taichung City was reflected in all variables as being affected by the exogenous variable, local government expenditure. Although the industrialized city of Kaohsiung is faced with the growing problem of a loss of jobs, along with a housing market recession in recent years, the city’s net population migration has thus far been unaffected
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