345 research outputs found
Next-to-leading order QCD corrections to Z boson pair production via vector-boson fusion
Vector-boson fusion processes are an important tool for the study of
electroweak symmetry breaking at hadron colliders, since they allow to
distinguish a light Higgs boson scenario from strong weak boson scattering. We
here consider the channels WW->ZZ and ZZ->ZZ as part of electroweak Z boson
pair production in association with two tagging jets. We present the
calculation of the NLO QCD corrections to the cross sections for p p -> e+ e-
mu+ mu- + 2 jets and p p -> e+ e- nu_mu nubar_mu + 2 jets via vector-boson
fusion at order alpha_s alpha^6, which is performed in the form a NLO
parton-level Monte Carlo program. The corrections to the integrated cross
sections are found to be modest, while the shapes of some kinematical
distributions change appreciably at NLO. Residual scale uncertainties typically
are at the few percent level.Comment: 12 pages, 4 figure
Adsorption of rare-gas atoms on Cu(111) and Pb(111) surfaces by van der Waals-corrected Density Functional Theory
The DFT/vdW-WF method, recently developed to include the Van der Waals
interactions in Density Functional Theory (DFT) using the Maximally Localized
Wannier functions, is applied to the study of the adsorption of rare-gas atoms
(Ne, Ar, Kr, and Xe) on the Cu(111) and Pb(111) surfaces, at three
high-symmetry sites. We evaluate the equilibrium binding energies and
distances, and the induced work-function changes and dipole moments. We find
that, for Ne, Ar, and Kr on the Cu(111) surface the different adsorption
configurations are characterized by very similar binding energies, while the
favored adsorption site for Xe on Cu(111) is on top of a Cu atom, in agreement
with previous theoretical calculations and experimental findings, and in common
with other close-packed metal surfaces. Instead, the favored site is always the
hollow one on the Pb(111) surface, which therefore represents an interesting
system where the investigation of high-coordination sites is possible.
Moreover, the Pb(111) substrate is subject, upon rare-gas adsorption, to a
significantly smaller change in the work function (and to a correspondingly
smaller induced dipole moment) than Cu(111). The role of the chosen reference
DFT functional and of different Van der Waals corrections, and their dependence
on different rare-gas adatoms, are also discussed
Solutions to Maxwell's Equations using Spheroidal Coordinates
Analytical solutions to the wave equation in spheroidal coordinates in the
short wavelength limit are considered. The asymptotic solutions for the radial
function are significantly simplified, allowing scalar spheroidal wave
functions to be defined in a form which is directly reminiscent of the
Laguerre-Gaussian solutions to the paraxial wave equation in optics.
Expressions for the Cartesian derivatives of the scalar spheroidal wave
functions are derived, leading to a new set of vector solutions to Maxwell's
equations. The results are an ideal starting point for calculations of
corrections to the paraxial approximation
Next-to-leading order QCD corrections to W+W- production via vector-boson fusion
Vector-boson fusion processes constitute an important class of reactions at
hadron colliders, both for signals and backgrounds of new physics in the
electroweak interactions.
We consider what is commonly referred to as W+W- production via vector-boson
fusion (with subsequent leptonic decay of the Ws), or, more precisely, e+ nu_e
mu- nubar_mu + 2 jets production in proton-proton scattering, with all resonant
and non-resonant Feynman diagrams and spin correlations of the final-state
leptons included, in the phase-space regions which are dominated by t-channel
electroweak-boson exchange.
We compute the next-to-leading order QCD corrections to this process, at
order alpha^6 alpha_s.
The QCD corrections are modest, changing total cross sections by less than
10%. Remaining scale uncertainties are below 2%. A fully-flexible
next-to-leading order partonic Monte Carlo program allows to demonstrate these
features for cross sections within typical vector-boson-fusion acceptance cuts.
Modest corrections are also found for distributions.Comment: 29 pages, 14 figure
Sisyphus Cooling of Electrically Trapped Polyatomic Molecules
The rich internal structure and long-range dipole-dipole interactions
establish polar molecules as unique instruments for quantum-controlled
applications and fundamental investigations. Their potential fully unfolds at
ultracold temperatures, where a plethora of effects is predicted in many-body
physics, quantum information science, ultracold chemistry, and physics beyond
the standard model. These objectives have inspired the development of a wide
range of methods to produce cold molecular ensembles. However, cooling
polyatomic molecules to ultracold temperatures has until now seemed
intractable. Here we report on the experimental realization of opto-electrical
cooling, a paradigm-changing cooling and accumulation method for polar
molecules. Its key attribute is the removal of a large fraction of a molecule's
kinetic energy in each step of the cooling cycle via a Sisyphus effect,
allowing cooling with only few dissipative decay processes. We demonstrate its
potential by reducing the temperature of about 10^6 trapped CH_3F molecules by
a factor of 13.5, with the phase-space density increased by a factor of 29 or a
factor of 70 discounting trap losses. In contrast to other cooling mechanisms,
our scheme proceeds in a trap, cools in all three dimensions, and works for a
large variety of polar molecules. With no fundamental temperature limit
anticipated down to the photon-recoil temperature in the nanokelvin range, our
method eliminates the primary hurdle in producing ultracold polyatomic
molecules. The low temperatures, large molecule numbers and long trapping times
up to 27 s will allow an interaction-dominated regime to be attained, enabling
collision studies and investigation of evaporative cooling toward a BEC of
polyatomic molecules
Generic User Process Interface for Event Generators
Generic Fortran common blocks are presented for use by High Energy Physics
event generators for the transfer of event configurations from parton level
generators to showering and hadronization event generators.Comment: Physics at TeV Colliders II Workshop, Les Houches, France, May 2001
14 pages, 6 figure
Dominant next-to-leading order QCD corrections to Higgs plus three jet production in vector-boson fusion
We present the calculation of the dominant next to leading order QCD
corrections to Higgs boson production in association with three jets via vector
boson fusion in the form of a NLO parton-level Monte Carlo program. QCD
corrections to integrated cross sections are modest, while the shapes of some
kinematical distributions change appreciably at NLO. Scale uncertainties are
shown to be reduced at NLO for the total cross section and for distributions.
We consider a central jet veto at the LHC and analyze the veto probability for
typical vector boson fusion cuts. Scale uncertainties of the veto probability
are sufficiently small at NLO for precise Higgs coupling measurements at the
LHC.Comment: 40 pages, 17 figures, 2 tables, published versio
Unitarization of Gluon Exchange Amplitudes and Rapidity Gaps at the Tevatron
Rapidity gaps between two hard jets at the Tevatron have been interpreted as
being due to the exchange of two gluons which are in an overall color-singlet
state. We show that this simple picture involves unitarity violating
amplitudes. Unitarizing the gluon exchange amplitude leads to qualitatively
different predictions for the fraction of -channel color singlet exchange
events in forward , or scattering, which better fit Tevatron
data.Comment: 21 pages, Revtex, 7 postscript figures included via epsf.sty.
Compressed postscript file of complete paper also available at
http://pheno.physics.wisc.edu/pub/preprints/1998/madph-98-1024.ps.Z or at
ftp://pheno.physics.wisc.edu/pub/preprints/1998/madph-98-1024.ps.
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