17,283 research outputs found
Diffractive Higgs boson photoproduction in peripheral collisions
An alternative process is proposed for the diffractive Higgs boson production
in peripheral collisions, exploring it through the photon-proton
interaction by Double Pomeron Exchange. It is estimated the event rate of the
diffractive Higgs production in central rapidity for Tevatron and LHC energies,
being of the order of 1 fb, in agreement to the predictions from other
diffractive processes. The results are confronted with those obtained from a
similar approach of the Durham group.Comment: 4 pages, 7 figures, contribution to the proceedings of II Latin
American Workshop on High Energy Physics [IILAWHEP], 3-7 Dec. 2007, Sao
Miguel das Missoes, Brazi
Single and Central Diffractive Higgs Production at the LHC
The single and central diffractive production of the Standard Model Higgs
boson is computed using the diffractive factorization formalism, taking into
account a parametrization for the Pomeron structure function provided by the H1
Collaboration. We compute the cross sections at NLO accuracy for the gluon
fusion process, since it is the leading mechanism for the Higgs boson
production. The gap survival probability is also introduced to include the
rescattering corrections due to spectator particles present in the interaction.
The diffractive ratios are predicted for proton-proton collisions at the LHC,
since the beam luminosity is favorable to the Higgs boson detection. These
results provide updated estimations for the fraction of single and central
diffractive events in the LHC kinematical regime.Comment: To appear in the proceedings of Diffraction 2010: International
Workshop on Diffraction in High Energy Physics, Otranto, Italy, 10-15 Sep
201
Soft and hard QCD dynamics in hadroproduction of charmonium
Both hard and soft QCD dynamics are important in charmonium production, as
presented here through a next-to-leading order QCD matrix element calculation
combined with the colour evaporation model. Observed and
distributions of in hadroproduction at fixed target and
collider energies are reproduced. Quite similar results can also be obtained in
a more phenomenologically useful Monte Carlo event generator where the
perturbative production of \ccbar pairs is instead obtained through leading
order matrix elements and the parton shower approximation of the higher order
processes. The soft dynamics may alternatively be described by the soft colour
interaction model, originally introduced in connection with rapidity gaps. We
also discuss the relative rates of different charmonium states and introduce an
improved model for mapping the continuous \ccbar mass spectrum on the physical
charmonium resonances.Comment: 21 pages, 13 eps figure
Soft and hard QCD in charmonium production
Hard and soft QCD dynamics are both important in charmonium hadroproduction,
as presented here through a next-to-leading order QCD matrix element
calculation combined with the colour evaporation model. Observed and
distributions of in hadroproduction are reproduced. Quite
similar results can also be obtained with a Monte Carlo event generator where
\ccbar pairs are instead produced through leading order matrix elements and the
parton shower approximation of higher order processes. The soft dynamics may
alternatively be described by the soft colour interaction model. We also
discuss the relative rates of different charmonium states and introduce an
improved model for mapping the continuous ccbar mass spectrum on the physical
charmonium resonances.Comment: Presented at Pan American Advanced Studies Institute (PASI 2002),
Campos do Jord\~ao, Brazil, January 7-18, 200
Criterion for purely elastic Taylor-Couette instability in the flows of shear-banding fluids
In the past twenty years, shear-banding flows have been probed by various
techniques, such as rheometry, velocimetry and flow birefringence. In micellar
solutions, many of the data collected exhibit unexplained spatio-temporal
fluctuations. Recently, it has been suggested that those fluctuations originate
from a purely elastic instability of the flow. In cylindrical Couette geometry,
the instability is reminiscent of the Taylor-like instability observed in
viscoelastic polymer solutions. In this letter, we describe how the criterion
for purely elastic Taylor-Couette instability should be adapted to
shear-banding flows. We derive three categories of shear-banding flows with
curved streamlines, depending on their stability.Comment: 6 pages, 3 figure
Dynamics of the peel front and the nature of acoustic emission during peeling of an adhesive tape
We investigate the peel front dynamics and acoustic emission of an adhesive
tape within the context of a recent model by including an additional
dissipative energy that mimics bursts of acoustic signals. We find that the
nature of the peeling front can vary from smooth to stuck-peeled configuration
depending on the values of dissipation coefficient, inertia of the roller, mass
of the tape. Interestingly, we find that the distribution of AE bursts shows a
power law statistics with two scaling regimes with increasing pull velocity as
observed in experiments. In this regimes, the stuck-peeled configuration is
similar to the `edge of peeling' reminiscent of a system driven to a critical
state.Comment: Accepted for publication in Phys. Rev. Let
Potential "ways of thinking" about the shear-banding phenomenon
Shear-banding is a curious but ubiquitous phenomenon occurring in soft
matter. The phenomenological similarities between the shear-banding transition
and phase transitions has pushed some researchers to adopt a 'thermodynamical'
approach, in opposition to the more classical 'mechanical' approach to fluid
flows. In this heuristic review, we describe why the apparent dichotomy between
those approaches has slowly faded away over the years. To support our
discussion, we give an overview of different interpretations of a single
equation, the diffusive Johnson-Segalman (dJS) equation, in the context of
shear-banding. We restrict ourselves to dJS, but we show that the equation can
be written in various equivalent forms usually associated with opposite
approaches. We first review briefly the origin of the dJS model and its initial
rheological interpretation in the context of shear-banding. Then we describe
the analogy between dJS and reaction-diffusion equations. In the case of
anisotropic diffusion, we show how the dJS governing equations for steady shear
flow are analogous to the equations of the dynamics of a particle in a quartic
potential. Going beyond the existing literature, we then draw on the Lagrangian
formalism to describe how the boundary conditions can have a key impact on the
banding state. Finally, we reinterpret the dJS equation again and we show that
a rigorous effective free energy can be constructed, in the spirit of early
thermodynamic interpretations or in terms of more recent approaches exploiting
the language of irreversible thermodynamics.Comment: 14 pages, 6 figures, tutorial revie
Energy efficient engine. Low pressure turbine test hardware detailed design report
The low pressure turbine for the energy efficient engine is a five-stage configuration with moderate aerodynamic loading incorporating advanced features of decambered airfoils and extended blade overlaps at platforms and shrouds. Mechanical integrity of 18,000 hours on flowpath components and 36,000 hours on all other components is achieved along with no aeromechanical instabilities within the steady-state operating range. Selection of a large number (156) of stage 4 blades, together with an increased stage 4 vane-to-blade gap, assists in achieving FAR 36 acoustic goals. Active clearance control (ACC) of gaps at blade tips and interstage seals is achieved by fan air cooling judiciously applied at responsive locations on the casing. This ACC system is a major improvement in preventing deterioration of the 0.0381 cm (0.015 in.) clearances required to meet the integrated-core/low-spool turbine efficiency goal of 91.1% and the light propulsion system efficiency goal of 91.7%
Inclusive hadron and photon production at LHC in dipole momentum space
Using a momentum space model for the dipole scattering amplitude we present
an analysis of the saturation effects at LHC energies, describing the data on
proton-proton and proton-lead collisions. The model is based on the asymptotic
solutions of the Balitsky-Kovchegov equation, being ideal in the saturation
domain where the target wave function has a high occupation number. We also
make predictions for the nuclear modification ratios on charged hadron and
prompt photon production in the forward region, where the high parton density
effects are important.Comment: New section added and typos corrected. To be published in PR
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