644 research outputs found
Automation of the matrix element reweighting method
Matrix element reweighting is a powerful experimental technique widely
employed to maximize the amount of information that can be extracted from a
collider data set. We present a procedure that allows to automatically evaluate
the weights for any process of interest in the standard model and beyond. Given
the initial, intermediate and final state particles, and the transfer functions
for the final physics objects, such as leptons, jets, missing transverse
energy, our algorithm creates a phase-space mapping designed to efficiently
perform the integration of the squared matrix element and the transfer
functions. The implementation builds up on MadGraph, it is completely
automatized and publicly available. A few sample applications are presented
that show the capabilities of the code and illustrate the possibilities for new
studies that such an approach opens up.Comment: 41 pages, 21 figure
DELPHES 3, A modular framework for fast simulation of a generic collider experiment
The version 3.0 of the DELPHES fast-simulation is presented. The goal of
DELPHES is to allow the simulation of a multipurpose detector for
phenomenological studies. The simulation includes a track propagation system
embedded in a magnetic field, electromagnetic and hadron calorimeters, and a
muon identification system. Physics objects that can be used for data analysis
are then reconstructed from the simulated detector response. These include
tracks and calorimeter deposits and high level objects such as isolated
electrons, jets, taus, and missing energy. The new modular approach allows for
greater flexibility in the design of the simulation and reconstruction
sequence. New features such as the particle-flow reconstruction approach,
crucial in the first years of the LHC, and pile-up simulation and mitigation,
which is needed for the simulation of the LHC detectors in the near future,
have also been implemented. The DELPHES framework is not meant to be used for
advanced detector studies, for which more accurate tools are needed. Although
some aspects of DELPHES are hadron collider specific, it is flexible enough to
be adapted to the needs of electron-positron collider experiments.Comment: JHEP 1402 (2014
Field-Driven Domain-Wall Dynamics in GaMnAs Films with Perpendicular Anisotropy
We combine magneto-optical imaging and a magnetic field pulse technique to
study domain wall dynamics in a ferromagnetic (Ga,Mn)As layer with
perpendicular easy axis. Contrary to ultrathin metallic layers, the depinning
field is found to be smaller than the Walker field, thereby allowing for the
observation of the steady and precessional flow regimes. The domain wall width
and damping parameters are determined self-consistently. The damping, 30 times
larger than the one deduced from ferromagnetic resonance, is shown to
essentially originate from the non-conservation of the magnetization modulus.
An unpredicted damping resonance and a dissipation regime associated with the
existence of horizontal Bloch lines are also revealed
Expansion-Free Evolving Spheres Must Have Inhomogeneous Energy Density Distributions
In a recent paper a systematic study on shearing expansion-free spherically
symmetric distributions was presented. As a particular case of such systems,
the Skripkin model was mentioned, which corresponds to a nondissipative perfect
fluid with a constant energy density. Here we show that such a model is
inconsistent with junction conditions. It is shown that in general for any
nondissipative fluid distribution, the expansion-free condition requires the
energy density to be inhomogeneous. As an example we consider the case of dust,
which allows for a complete integration.Comment: 8 pages, Latex. To appear in Phys. Rev.D. Typos correcte
Expansion-Free Cavity Evolution: Some exact Analytical Models
We consider spherically symmetric distributions of anisotropic fluids with a
central vacuum cavity, evolving under the condition of vanishing expansion
scalar. Some analytical solutions are found satisfying Darmois junction
conditions on both delimiting boundary surfaces, while some others require the
presence of thin shells on either (or both) boundary surfaces. The solutions
here obtained model the evolution of the vacuum cavity and the surrounding
fluid distribution, emerging after a central explosion. This study complements
a previously published work where modeling of the evolution of such kind of
systems was achieved through a different kinematical condition.Comment: 9 pages, Revtex. Typos corrected. Published in Int. J. Mod. Phys.
Double Distribution of Dark Matter Halos with respect to Mass and Local Overdensity
We present a double distribution function of dark matter halos, with respect
to both object mass and local over- (or under-) density. This analytical tool
provides a statistical treatment of the properties of matter surrounding
collapsed objects, and can be used to study environmental effects on
hierarchical structure formation. The size of the "local environment" of a
collapsed object is defined to depend on the mass of the object. The
Press-Schechter mass function is recovered by integration of our double
distribution over the density contrast. We also present a detailed treatment of
the evolution of overdensities and underdensities in Einstein-deSitter and flat
LCDM universes, according to the spherical evolution model. We explicitly
distinguish between true and linearly extrapolated overdensities and provide
conversion relations between the two quantities.Comment: 25 pages, 10 figures, comments welcom
Determination of the micromagnetic parameters in (Ga,Mn)As using domain theory
The magnetic domain structure and magnetic properties of a ferromagnetic
(Ga,Mn)As epilayer with perpendicular magnetic easy-axis are investigated. We
show that, despite strong hysteresis, domain theory at thermodynamical
equilibrium can be used to determine the micromagnetic parameters. Combining
magneto-optical Kerr microscopy, magnetometry and ferromagnetic resonance
measurements, we obtain the characteristic parameter for magnetic domains
, the domain wall width and specific energy, and the spin stiffness
constant as a function of temperature. The nucleation barrier for magnetization
reversal and the Walker breakdown velocity for field-driven domain wall
propagation are also estimated
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