2,663 research outputs found
Resonance-free Region in scattering by a strictly convex obstacle
We prove the existence of a resonance free region in scattering by a strictly
convex obstacle with the Robin boundary condition. More precisely, we show that
the scattering resonances lie below a cubic curve which is the same as in the
case of the Neumann boundary condition. This generalizes earlier results on
cubic poles free regions obtained for the Dirichlet boundary condition.Comment: 29 pages, 2 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
Using Rapidity Gaps to Distinguish Between Higgs Production by W and Gluon Fusion
The possibility of distinguishing between two higgs production mechanisms, W
fusion and gluon fusion, is investigated using the Monte Carlo event generator
PYTHIA. It is shown that, considering the designed CM energy and luminosity for
the LHC, it is not possible to distinguish between the two higgs production
processes as, for a given integrated luminosity, they lead to the same number
of events containing a rapidity gap.Comment: uudecoded compressed tar file containing a tex file and 6 figure
files. Two more figures, avaiable from the authors upon reques
The CCFM Monte Carlo generator CASCADE
CASCADE is a full hadron level Monte Carlo event generator for e-p, gamma-p
and p-p_bar processes, which uses the CCFM evolution equation for the initial
state cascade in a backward evolution approach supplemented with off-shell
matrix elements for the hard scattering. A detailed program description is
given, with emphasis on parameters the user wants to change and common block
variables which completely specify the generated events.Comment: Program manual, 14 page
Fractal Weyl laws for chaotic open systems
We present a result relating the density of quantum resonances for an open
chaotic system to the fractal dimension of the associated classical repeller.
The result is supported by numerical computation of the resonances of the
system of n disks on a plane. The result generalizes the Weyl law for the
density of states of a closed system to chaotic open systems.Comment: revtex4, 4 pages, 3 figure
Matrix-Element Corrections to Parton Shower Algorithms
We discuss two ways in which parton shower algorithms can be supplemented by
matrix-element corrections to ensure the correct hard limit: by using
complementary phase-space regions, or by modifying the shower itself. In the
former case, existing algorithms are self-consistent only if the total
correction is small. In the latter case, existing algorithms are never
self-consistent, a problem that is particularly severe for angular-ordered
parton shower algorithms. We show how to construct self-consistent algorithms
in both cases. The postscript file for this paper can also be obtained by
anonymous ftp from thep.lu.se in the file pub/Preprints/lu_tp_94_17.psComment: 11 pages, LU TP 94-1
On multiplicity correlations in the STAR data
The STAR data on the multiplicity correlations between narrow psudorapidity
bins in the pp and AuAu collisions are discussed. The PYTHIA 8.145 generator is
used for the pp data, and a naive superposition model is presented for the AuAu
data. It is shown that the PYTHIA generator with default parameter values
describes the pp data reasonably well, whereas the superposition model fails to
reproduce the centrality dependence seen in the data. Some possible reasons for
this failure and a comparison with other models are presented.Comment: 8 pages, 3 figure
Initial-state parton shower kinematics for NLO event generators
We are developing a consistent method to combine tree-level event generators
for hadron collision interactions with those including one additional QCD
radiation from the initial-state partons, based on the limited leading-log
(LLL) subtraction method, aiming at an application to NLO event generators. In
this method, a boundary between non-radiative and radiative processes
necessarily appears at the factorization scale (mu_F). The radiation effects
are simulated using a parton shower (PS) in non-radiative processes. It is
therefore crucial in our method to apply a PS which well reproduces the
radiation activities evaluated from the matrix-element (ME) calculations for
radiative processes. The PS activity depends on the applied kinematics model.
In this paper we introduce two models for our simple initial-state leading-log
PS: a model similar to the "old" PYTHIA-PS and a p_T-prefixed model motivated
by ME calculations. PS simulations employing these models are tested using
W-boson production at LHC as an example. Both simulations show a smooth
matching to the LLL-subtracted W + 1 jet simulation in the p_T distribution of
W bosons, and the summed p_T spectra are stable against a variation of mu_F,
despite that the p_T-prefixed PS results in an apparently harder p_T spectrum.Comment: 10 pages, 6 figures; minor changes in the abstract and the text
according to the comments from the refere
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