46,224 research outputs found
Angular correlations in multi-jet final states from kt-dependent parton showers
We investigate parton-branching methods based on transverse-momentum
dependent (TMD) parton distributions and matrix elements for the Monte Carlo
simulation of multi-particle final states at high-energy colliders. We observe
that recently measured angular correlations in ep final states with multiple
hadronic jets probe QCD coherence effects in the space-like branching,
associated with finite-angle gluon radiation from partons carrying small
longitudinal momenta, and not included in standard shower generators. We
present Monte Carlo calculations for azimuthal two-jet and three-jet
distributions, for jet multiplicities and for correlations in the
transverse-momentum imbalance between the leading jets. We discuss comparisons
with current experimental multi-jet data, and implications of corrections to
collinear-ordered showers for LHC final states.Comment: 25 pages. Discussion and references expanded; results unchanged.
Additional calculations include
Space shuttle: Basic subsonic static aerodynamic characteristics for Grumman H-33 orbiter configuration (M equals 0.17)
Results of an experimental aerodynamic investigation of the H-33 space orbiter are presented. The investigation was undertaken to determine static aerodynamic characteristics of the orbiter at a Mach number of 0.17. These data were determined by employing a 1/25 scale model of the orbiter for pitch and yaw variations of -4 degrees to 24 degrees to 15 degrees, respectively. Investigations were conducted in the 7 - by - 10 foot wind tunnel
Hadroproduction of electroweak gauge boson plus jets and TMD parton density functions
If studies of electroweak gauge boson final states at the Large Hadron
Collider, for Standard Model physics and beyond, are sensitive to effects of
the initial state's transverse momentum distribution, appropriate
generalizations of QCD shower evolution are required. We propose a method to do
this based on QCD transverse momentum dependent (TMD) factorization at high
energy. The method incorporates experimental information from the
high-precision deep inelastic scattering (DIS) measurements, and includes
experimental and theoretical uncertainties on TMD parton density functions. We
illustrate the approach presenting results for production of W-boson + n jets
at the LHC, including azimuthal correlations and subleading jet distributions.Comment: 9 pages, 4 figures. v2: comments and references added, typos
corrected; results unchange
A kT-dependent sea-quark density for the CASCADE Monte Carlo event generator
Parton-shower event generators that go beyond the collinear-ordering
approximation at small x have so far included only gluon and valence quark
channels at transverse momentum dependent level. We describe results of recent
work to include effects of the sea-quark distribution with explicit dependence
on the transverse quark-momentum.This sea-quark density is then applied to the
description of forward Z -production. The qq*->Z matrix element (with one
off-shell quark) is calculated in an explicit gauge invariant way, making use
of high energy factorization. The kT-factorized result has been implemented
into the CCFM Monte-Carlo CASCADE and a numerical comparison with the qg*->Zq
matrix element has been carried out.Comment: 4 pages, 4 figures, based on a talk given at the XXI Workshop on
Deep-Inelastic Scattering and Related Subjects, 11-15 April, Newport News,
Virginia (2011
The CCFM uPDF evolution uPDFevolv
uPDFevolv is an evolution code for TMD parton densities using the CCFM
evolution equation. A description of the underlying theoretical model and
technical realization is given together with a detailed program description,
with emphasis on parameters the user may want to changeComment: Code and description on https://updfevolv.hepforge.org Version to be
published in EPJ
Treating jet correlations in high pile-up at hadron colliders
Experiments in the high-luminosity runs at the Large Hadron Collider face the
challenges of very large pile-up. Primary techniques to deal with this are
based on precise vertex and track reconstruction. Outside tracker acceptances,
however, lie regions of interest for many aspects of the LHC physics program.
We explore complementary approaches to pile-up treatment and propose a
data-driven jet-mixing method which can be used outside tracker acceptances
without depending on Monte Carlo generators. The method can be applied to treat
correlation observables and take into account, besides the jet transverse
momentum pedestal, effects of hard jets from pile-up.Comment: Latex. 8 pages, 5 figure
Multi-scale simulations of black hole accretion in barred galaxies: Self-gravitating disk models
Due to the non-axisymmetric potential of the central bar, barred spiral
galaxies form, in addition to their characteristic arms and bar, a variety of
structures within the thin gas disk, like nuclear rings, inner spirals and
dust-lanes. These structures in the inner kiloparsec are most important to
explain and understand the rate of black hole feeding. The aim of this work is
to investigate the influence of stellar bars in spiral galaxies on the thin
self-gravitating gas disk. We focus on the accretion of gas onto the central
supermassive black hole and its time-dependent evolution. We conduct
multi-scale simulations simultaneously resolving the galactic disk and the
accretion disk around the central black-hole. We vary in all simulations the
initial gas disk mass. As additional parameter we choose either the gas
temperature for isothermal simulations or the cooling timescale in case of
non-isothermal simulations. Accretion is either driven by a gravitationally
unstable or clumpy accretion disk or by energy dissipation in strong shocks.
Most simulations show a strong dependence of the accretion rate at the outer
boundary of the central accretion disk () on the gas flow
at kiloparsec scales. The final black hole masses reach up to after . Our models show the expected influence of
the Eddington limit and a decline in growth rate at the corresponding
sub-Eddington limit
Space Charge Effects in Ferroelectric Thin Films
The effects of space charges on hysteresis loops and field distributions in
ferroelectrics have been investigated numerically using the phenomenological
Landau-Ginzburg-Devonshire theory. Cases with the ferroelectric fully and
partially depleted have been considered. In general, increasing the number of
charged impurities results in a lowering of the polarization and coercive field
values. Squarer loops were observed in the partially depleted cases and a
method was proposed to identify fully depleted samples experimentally from
dielectric and polarization measurements alone. Unusual field distributions
found for higher dopant concentrations have some interesting implications for
leakage mechanisms and limit the range of validity of usual semiconductor
equations for carrier transport.Comment: 23 pages, 11 figure
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