239 research outputs found
Non-global logarithms in inter-jet energy flow with kt clustering requirement
Recent work in inter-jet energy flow has identified a class of leading
logarithms previously not considered in the literature. These so-called
non-global logarithms have been shown to have significant numerical impact on
gaps-between-jets calculations at the energies of current particle colliders.
Here we calculate, at fixed order and to all orders, the effect of applying
clustering to the gluonic final state responsible for these logarithms for a
trivial colour flow 2 jet system. Such a clustering algorithm has already been
used for experimental measurements at HERA. We find that the impact of the
non-global logarithms is reduced, but not removed, when clustering is demanded,
a result which is of considerable interest for energy flow observable
calculations.Comment: 13 pages, 4 figure
FastJet user manual
FastJet is a C++ package that provides a broad range of jet finding and
analysis tools. It includes efficient native implementations of all widely used
2-to-1 sequential recombination jet algorithms for pp and e+e- collisions, as
well as access to 3rd party jet algorithms through a plugin mechanism,
including all currently used cone algorithms. FastJet also provides means to
facilitate the manipulation of jet substructure, including some common boosted
heavy-object taggers, as well as tools for estimation of pileup and
underlying-event noise levels, determination of jet areas and subtraction or
suppression of noise in jets.Comment: 69 pages. FastJet 3 is available from http://fastjet.fr
Polarizing the Dipoles
We extend the massless dipole formalism of Catani and Seymour, as well as its
massive version as developed by Catani, Dittmaier, Seymour and Trocsanyi, to
arbitrary helicity eigenstates of the external partons. We modify the real
radiation subtraction terms only, the primary aim being an improved efficiency
of the numerical Monte Carlo integration of this contribution as part of a
complete next-to-leading order calculation. In consequence, our extension is
only applicable to unpolarized scattering. Upon summation over the helicities
of the emitter pairs, our formulae trivially reduce to their original form. We
implement our extension within the framework of Helac-Phegas, and give some
examples of results pertinent to recent studies of backgrounds for the LHC. The
code is publicly available. Since the integrated dipole contributions do not
require any modifications, we do not discuss them, but they are implemented in
the software.Comment: 20 pages, 4 figures, Integrated dipoles implemented for massless and
massive case
Probing Heavy Higgs Boson Models with a TeV Linear Collider
The last years have seen a great development in our understanding of particle
physics at the weak scale. Precision electroweak observables have played a key
role in this process and their values are consistent, within the Standard Model
interpretation, with a light Higgs boson with mass lower than about 200 GeV. If
new physics were responsible for the mechanism of electroweak symmetry
breaking, there would, quite generally, be modifications to this prediction
induced by the non-standard contributions to the precision electroweak
observables. In this article, we analyze the experimental signatures of a heavy
Higgs boson at linear colliders. We show that a linear collider, with center of
mass energy \sqrt{s} <= 1 TeV, would be very useful to probe the basic
ingredients of well motivated heavy Higgs boson models: a relatively heavy
SM-like Higgs, together with either extra scalar or fermionic degrees of
freedom, or with the mixing of the third generation quarks with non-standard
heavy quark modes.Comment: 21 page
Soft gluons in Higgs plus two jet production
We investigate the effects of an all order QCD resummation of soft gluon
emissions for Higgs boson production in association with two hard jets. We
consider both the gluon-gluon fusion and weak boson fusion processes and show
how to resum a large part of the leading logarithms in the jet veto scale. Our
resummation improves on previous analyses which also aim to include the effects
of multiple soft gluon radiation. In addition we calculate the interference
between weak boson fusion and gluon-gluon fusion and find that it is small.Comment: 15 pages and 5 figure
Understanding X ray Photoelectron Spectra of Ionic Liquids Experiments and Simulations of 1 Butyl 3 methylimidazolium Thiocyanate
We demonstrate a combined experimental and computational approach to probe the electronic structure and atomic environment of an ionic liquid, based on core level binding energies. The 1 butyl 3 methylimidazolium thiocyanate [C4C1Im][SCN] ionic liquid was studied using ab initio molecular dynamics, and results were compared against previously published and new experimental X ray photoelectron spectroscopy XPS data. The long held assumption that initial state effects in XPS dominate the measured binding energies is proven correct, which validates the established premise that the ground state electronic structure of the ionic liquid can be inferred directly from XPS measurements. A regression model based upon site electrostatic potentials and intramolecular bond lengths is shown to account accurately for variations in core level binding energies within the ionic liquid, demonstrating the important effect of long range interactions on the core levels and throwing into question the validity of traditional single ion pair ionic liquid calculations for interpreting XPS dat
How well can the LHC distinguish between the SM light Higgs scenario, a composite Higgs and the Higgsless case using VV scattering channels?
A complete parton level analysis of ll + four jets l = e,mu and 3lv + two
jets production at the LHC is presented, including all processes at order
\ordEW, \ordQCD and \ordQCDsq when appropriate. The infinite Higgs mass
scenario, which is considered as a benchmark for strong scattering theories and
is the limiting case for composite Higgs models, and one example of a model
incorporating a Strongly Interacting Light Higgs are confronted with the
Standard Model light Higgs predictions. This analysis is combined with the
results in the lv + four jets channel presented in a previous paper, in order
to determine whether a composite Higgs signal can be detected as an excess of
events in boson--boson scattering.Comment: Introduced some representative Feynman diagrams. Rearranged section
4. Typos fixed. Published in JHE
Multiparton Interactions in Photoproduction at HERA
The high energy photoproduction of jets is being observed at the ep collider,
HERA. It may be that the HERA centre-of-mass energy is sufficiently large that
the production of more than one pair of jets per ep collision becomes possible,
owing to the large number density of the probed gluons. We construct a Monte
Carlo model of such multiparton interactions and study their effects on a wide
range of physical observables. The conclusion is that multiple interactions
could have very significant effects upon the photoproduction final state and
that this would for example make extractions of the gluon density in the photon
rather difficult. Total rates for the production of many (i.e. > 2) jets could
provide direct evidence for the presence of multiple interactions, although
parton showering and hadronization significantly affect low transverse energy
jets.Comment: 21 pages, 8 figures include
Improved Understanding of Atomic Ordering in Y4SixAl2- xO9- xNxMaterials Using a Combined Solid-State NMR and Computational Approach
Ceramics based around silicon aluminum oxynitrides are of both fundamental structural chemistry and technological interest. Certain oxynitride crystal structures allow very significant compositional variation through extensive Si/N exchange for Al/O, which implies a degree of atomic ordering. In this study, solid-state 29Si MAS NMR and variable field 1D and 2D 27Al MAS NMR measurements are combined with density functional theory calculations of both the structural and NMR interaction parameters for various points across the Y4Si2O7N2-Y4Al2O9 compositional range. This series provides numerous possibilities for significant variation of atomic ordering in the local ditetrahedral (Si,Al)2O7-xNx units. The two slightly structurally inequivalent aluminum sites in Y4Al2O9 are unambiguously assigned to the observed resonances. Computational findings on Y4Si2O7N2 demonstrate that the single observed 29Si NMR resonance covers a range of local inequivalent silicon environments. For the first time, the MAS NMR and neutron diffraction data from the Y4SiAlO8N structure have been directly reconciled, thus establishing aspects of atomic order and disorder that characterize this system. This comparison suggests that, although the diffraction data indicates long-range structural order supporting a highly crystalline character, the short-range information afforded by the solid-state NMR measurements indicates significant atomic disorder throughout the (Si,Al)2O7-xNx units
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