323,932 research outputs found
It's On: Early Interpretations of ATLAS Results in Jets and Missing Energy Searches
The first search for supersymmetry from ATLAS with 70/nb of integrated
luminosity extends the Tevatron' s reach for colored particles that decay into
jets plus missing transverse energy. For gluinos that decay directly or through
a one step cascade into the LSP and two jets, the mass range m_g < 205 GeV is
disfavored by the ATLAS searches, regardless of the mass of the LSP. In some
cases the coverage extends up to m_g ~ 295 GeV, already surpassing the
Tevatron's reach for compressed supersymmetry spectra.Comment: 5 pages, 3 figures, 1 table; references and figure added; Physics
Letters B (2011
Data-Driven Time-Frequency Analysis
In this paper, we introduce a new adaptive data analysis method to study
trend and instantaneous frequency of nonlinear and non-stationary data. This
method is inspired by the Empirical Mode Decomposition method (EMD) and the
recently developed compressed (compressive) sensing theory. The main idea is to
look for the sparsest representation of multiscale data within the largest
possible dictionary consisting of intrinsic mode functions of the form , where , consists of the
functions smoother than and . This problem can
be formulated as a nonlinear optimization problem. In order to solve this
optimization problem, we propose a nonlinear matching pursuit method by
generalizing the classical matching pursuit for the optimization problem.
One important advantage of this nonlinear matching pursuit method is it can be
implemented very efficiently and is very stable to noise. Further, we provide a
convergence analysis of our nonlinear matching pursuit method under certain
scale separation assumptions. Extensive numerical examples will be given to
demonstrate the robustness of our method and comparison will be made with the
EMD/EEMD method. We also apply our method to study data without scale
separation, data with intra-wave frequency modulation, and data with incomplete
or under-sampled data
Anomalous Momentum States, Non-Specular Reflections, and Negative Refraction of Phase-Locked, Second Harmonic Pulses
We simulate and discuss novel spatio-temporal propagation effects that relate
specifically to pulsed, phase-mismatched second harmonic generation in a
negative index material having finite length. Using a generic Drude model for
the dielectric permittivity and magnetic permeability, the fundamental and
second harmonic frequencies are tuned so that the respective indices of
refraction are negative for the pump and positive for the second harmonic
signal. A phase-locking mechanism causes part of the second harmonic signal
generated at the entry surface to become trapped and dragged along by the pump
and to refract negatively, even though the index of refraction at the second
harmonic frequency is positive. These circumstances culminate in the creation
of an anomalous state consisting of a forward-moving second harmonic wave
packet that has negative wave vector and momentum density, which in turn leads
to non-specular reflections at intervening material interfaces. The
forward-generated second harmonic signal trapped under the pump pulse
propagates forward, but has all the attributes of a reflected pulse, similar to
its twin counterpart generated at the surface and freely propagating backward
away from the interface. This describes a new state of negative refraction,
associated with nonlinear frequency conversion and parametric processes,
whereby a beam generated at the interface can refract negatively even though
the index of refraction at that wavelength is positive
Factorization and Resummation for Groomed Multi-Prong Jet Shapes
Observables which distinguish boosted topologies from QCD jets are playing an
increasingly important role at the Large Hadron Collider (LHC). These
observables are often used in conjunction with jet grooming algorithms, which
reduce contamination from both theoretical and experimental sources. In this
paper we derive factorization formulae for groomed multi-prong substructure
observables, focusing in particular on the groomed observable, which is
used to identify boosted hadronic decays of electroweak bosons at the LHC. Our
factorization formulae allow systematically improvable calculations of the
perturbative distribution and the resummation of logarithmically enhanced
terms in all regions of phase space using renormalization group evolution. They
include a novel factorization for the production of a soft subjet in the
presence of a grooming algorithm, in which clustering effects enter directly
into the hard matching. We use these factorization formulae to draw robust
conclusions of experimental relevance regarding the universality of the
distribution in both and collisions. In particular, we show that
the only process dependence is carried by the relative quark vs. gluon jet
fraction in the sample, no non-global logarithms from event-wide correlations
are present in the distribution, hadronization corrections are controlled by
the perturbative mass of the jet, and all global color correlations are
completely removed by grooming, making groomed a theoretically clean QCD
observable even in the LHC environment. We compute all ingredients to one-loop
accuracy, and present numerical results at next-to-leading logarithmic accuracy
for collisions, comparing with parton shower Monte Carlo simulations.
Results for collisions, as relevant for phenomenology at the LHC, are
presented in a companion paper.Comment: 66 pages, 18 figure
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