2,557 research outputs found
A sampling algorithm to estimate the effect of fluctuations in particle physics data
Background properties in experimental particle physics are typically
estimated using large data sets. However, different events can exhibit
different features because of the quantum mechanical nature of the underlying
physics processes. While signal and background fractions in a given data set
can be evaluated using a maximum likelihood estimator, the shapes of the
corresponding distributions are traditionally obtained using high-statistics
control samples, which normally neglects the effect of fluctuations. On the
other hand, if it was possible to subtract background using templates that take
fluctuations into account, this would be expected to improve the resolution of
the observables of interest, and to reduce systematics depending on the
analysis. This study is an initial step in this direction. We propose a novel
algorithm inspired by the Gibbs sampler that makes it possible to estimate the
shapes of signal and background probability density functions from a given
collection of particles, using control sample templates as initial conditions
and refining them to take into account the effect of fluctuations. Results on
Monte Carlo data are presented, and the prospects for future development are
discussed.Comment: 6 pages, 1 figure. Edited to improve readability in line with the
published article. This is based on a condensed version for publication in
the Proceedings of the International Conference on Mathematical Modelling in
the Physical Sciences, IC-MSQUARE 2012, Budapest, Hungary. A more detailed
discussion can be found in the preceding version of this arXiv recor
Search for SUSY in (Leptons +) Jets + E_T^miss final states
We study the observability of the squarks and gluinos in CMS at LHC.
Classical E_T^miss + jets final state as well as a number of additional
multilepton signatures (0 leptons, 1 lepton, 2 leptons of the same sign, 2
leptons of the opposite sign and 3 leptons) are investigated . The detection of
these sparticles relies on the observation of an excess of events over Standard
Model background expectations. The study is made in the framework of a minimal
SU(5) mSUGRA model as a function of m_0, m_1/2 for 4 sets of model parameters :
tan(beta) = 2 or 35 and sign(mu) = +/- 1 and for fixed value of A_0 = 0. The
CMS detector response is modelled using CMSJET 4.51 fast MC code (non-GEANT).
The results obtained are presented as 5 sigma detection contours in the m_0,
m_1/2 planes and with optimized selection cuts in various regions of the
parameter space. The result of these investigations is that with integrated
luminosity L=10^5 pb^-1 the squark and gluino mass reach is about 2.5 TeV and
covers most of the interesting parts of parameter space according to neutralino
relic density expectations. The influence of signal and background
cross-section uncertainties on the reach contours is estimated. The effect of
pile-up on signal and background is also discussed. This effect is found to be
insignificant for E_T^miss and single lepton signatures, whilst only a minor
deterioration is seen for multilepton final states.Comment: 28 pages, 28 figure
Energy Scaling of Minimum-Bias Tunes
We propose that the flexibility offered by modern event-generator tuning
tools allows for more than just obtaining "best fits" to a collection of data.
In particular, we argue that the universality of the underlying physics model
can be tested by performing several, mutually independent, optimizations of the
generator parameters in different physical regions. For regions in which these
optimizations return similar and self-consistent parameter values, the model
can be considered universal. Deviations from this behavior can be associated
with a breakdown of the modeling, with the nature of the deviations giving
clues as to the nature of the breakdown. We apply this procedure to study the
energy scaling of a class of minimum-bias models based on multiple parton
interactions (MPI) and pT-ordered showers, implemented in the Pythia 6.4
generator. We find that a parameter controlling the strength of color
reconnections in the final state is the most important source of
non-universality in this model.Comment: 17 pages, 3 figures, 4 table
Spectral functions of the half-filled 1D Hubbard chain within the exchange-correlation potential formalism
The spectral functions of the one-band half-filled 1D Hubbard chain are
calculated using the exchange-correlation potential formalism developed
recently. The exchange-correlation potential is adopted from the exact
potential derived from the Hubbard dimer. Within an approximation in which the
full Green function is replaced by a non-interacting one, the spectral
functions can be calculated analytically. Despite the simplicity of the
approximation, the resulting spectra are in favorable agreement with the more
accurate results obtained from the dynamic density-matrix renormalization group
method. In particular, the calculated band gap as a function of is in close
agreement with the exact gap obtained from the Bethe ansatz. In addition, the
formal general solution to the equation of motion of the Green function is
presented and the difference between the traditional self-energy approach and
the exchange-correlation potential formalism is also discussed and elaborated.
A simplified Holstein Hamiltonian is considered to further illustrate the
general form of the exchange-correlation potential.Comment: 10 pages, 7 figure
Resolvent estimates for normally hyperbolic trapped sets
We give pole free strips and estimates for resolvents of semiclassical
operators which, on the level of the classical flow, have normally hyperbolic
smooth trapped sets of codimension two in phase space. Such trapped sets are
structurally stable and our motivation comes partly from considering the wave
equation for Kerr black holes and their perturbations, whose trapped sets have
precisely this structure. We give applications including local smoothing
effects with epsilon derivative loss for the Schr\"odinger propagator as well
as local energy decay results for the wave equation.Comment: Further changes to erratum correcting small problems with Section 3.5
and Lemma 4.1; this now also corrects hypotheses, explicitly requiring
trapped set to be symplectic. Erratum follows references in this versio
Upper bound on the density of Ruelle resonances for Anosov flows
Using a semiclassical approach we show that the spectrum of a smooth Anosov
vector field V on a compact manifold is discrete (in suitable anisotropic
Sobolev spaces) and then we provide an upper bound for the density of
eigenvalues of the operator (-i)V, called Ruelle resonances, close to the real
axis and for large real parts.Comment: 57 page
On the Usefulness of Modulation Spaces in Deformation Quantization
We discuss the relevance to deformation quantization of Feichtinger's
modulation spaces, especially of the weighted Sjoestrand classes. These
function spaces are good classes of symbols of pseudo-differential operators
(observables). They have a widespread use in time-frequency analysis and
related topics, but are not very well-known in physics. It turns out that they
are particularly well adapted to the study of the Moyal star-product and of the
star-exponential.Comment: Submitte
Two- and three-particle azimuthal correlations of high-pt charged hadrons in Pb-Au collisions at 158A GeV/c
Azimuthal correlations of hadrons with high transverse momenta serve as a
measure to study the energy loss and the fragmentation pattern of jets emerging
from hard parton-parton interactions in heavy ion collisions. Preliminary
results from the CERES experiment on two- and three-particle correlations in
central Pb-Au collisions are presented. A strongly non-Gaussian shape on the
away-side of the two-particle correlation function is observed, indicating
significant interactions of the emerging partons with the medium. Mechanisms
like deflection of the initial partons or the evolution of a mach cone in the
medium can lead to similar modifications of the jet structure on the away-side.
An analysis based on three-particle correlations is presented which helps to
shed light on the origin of the observed away-side pattern.Comment: 4 pages, 2 figures, contribution to the Quark Matter conference 200
Color separate singlets in annihilation
We use the method of color effective Hamiltonian to study the properties of
states in which a gluonic subsystem forms a color singlet, and we will study
the possibility that such a subsystem hadronizes as a separate unit. A parton
system can normally be subdivided into singlet subsystems in many different
ways, and one problem arises from the fact that the corresponding states are
not orthogonal. We show that if only contributions of order are
included, the problem is greatly simplified. Only a very limited number of
states are possible, and we present an orthogonalization procedure for these
states. The result is simple and intuitive and could give an estimate of the
possibility to produce color separated gluonic subsystems, if no dynamical
effects are important. We also study with a simple MC the possibility that
configurations which correspond to "short strings" are dynamically favored. The
advantage of our approach over more elaborate models is its simplicity, which
makes it easier to estimate color reconnection effects in reactions which are
more complicated than the relatively simple annihilation.Comment: Revtex, 24 pages, 7 figures; Compared to the previous version, 1 new
figure is added and Monte-Carlo results are re-analyzed, as suggested by the
referee; To appear in Phys. Rev.
Spectral projections and resolvent bounds for partially elliptic quadratic differential operators
We study resolvents and spectral projections for quadratic differential
operators under an assumption of partial ellipticity. We establish
exponential-type resolvent bounds for these operators, including
Kramers-Fokker-Planck operators with quadratic potentials. For the norms of
spectral projections for these operators, we obtain complete asymptotic
expansions in dimension one, and for arbitrary dimension, we obtain exponential
upper bounds and the rate of exponential growth in a generic situation. We
furthermore obtain a complete characterization of those operators with
orthogonal spectral projections onto the ground state.Comment: 60 pages, 3 figures. J. Pseudo-Differ. Oper. Appl., to appear.
Revised according to referee report, including minor changes to Corollary
1.8. The final publication will be available at link.springer.co
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