1,598 research outputs found
The top induced backgrounds to Higgs production in the WW -> llvv decay channel at NLO in QCD
We present the complete NLO contributions to the pp -> e^+ v_e mu^- vbar_m b
bbar + X process in the four flavour scheme, i.e. with massive b quarks, and
its contribution to the H -> WW -> llvv measurement in the 1-jet bin at the
LHC. This background process includes top pair, single top and non-top
quark-resonant contributions. The uncertainty at NLO from renormalisation and
factorisation scale dependence is about +30% -20%. We show that the NLO
corrections are relatively small, and that separating this background in top
pair, Wt and b-quark associated llvv is a fair approximation.Comment: 4 pages, 5 figure
Extending the MINLO method
We consider improving POWHEG+MINLO simulations, so as to also render them NLO
accurate in the description of observables receiving contributions from events
with lower parton multiplicity than present in their underlying NLO
calculation. On a conceptual level we follow the strategy of the so-called
MINLO' programs. Whereas the existing MINLO' framework requires explicit
analytic input from higher order resummation, here we derive an effective
numerical approximation to these ingredients, by imposing unitarity. This
offers a way of extending the MINLO' method to more complex processes,
complementary to the known route which uses explicit computations of
high-accuracy resummation inputs. Specifically, we have focused on
Higgs-plus-two-jet production (HJJ) and related processes. We also consider how
one can cover three units of multiplicity at NLO accuracy, i.e. we consider how
the HJJ-MINLO simulation may yield NLO accuracy for inclusive H, HJ, and HJJ
quantities. We perform a feasibility study assessing the potential of these
ideas.Comment: 66 pages, 22 figures; v2 references added; v3=JHEP, improved
readabilit
Automation of the Dipole Subtraction Method in MadGraph/MadEvent
We present the implementation of the dipole subtraction formalism for the
real radiation contributions to any next-to-leading order QCD process in the
MadGraph/MadEvent framework. Both massless and massive dipoles are considered.
Starting from a specific (n+1)-particle process the package provides a Fortran
code for all possible dipoles to all Born processes that constitute the
subtraction term to the (n+1)-particle process. The output files are given in
the usual "MadGraph StandAlone" style using helicity amplitudes.Comment: 14 pages, 4 figure
Integrated dipoles with MadDipole in the MadGraph framework
Heading towards a full automation of next-to-leading order (NLO) QCD
corrections, one important ingredient is the analytical integration over the
one-particle phase space of the unresolved particle that is necessary when
adding the subtraction terms to the virtual corrections. We present the
implementation of these integrated dipoles in the MadGraph framework. The
result is a package that allows an automated calculation for the NLO real
emission parts of an arbitrary process.Comment: 22 pages, 1 figure. Published version: few reference updates and a
couple of minor corrections to the tex
T-odd Asymmetry in W+jet Events at the LHC
W bosons produced at high transverse momentum in hadron collisions can have
polarization along the direction perpendicular to the production plane, which
is odd under na\ddot{\i}ve-T-reversal where both the three-momenta and
angular momenta are reversed. Perturbative QCD predicts non-zero polarization
at the one-loop level, which can be measured as parity-odd components in the
angular distribution of charged leptons from the decay of W bosons. We perform
a detector-level simulation with the generator MadGraph5_aMC@NLO, and
demonstrate that the asymmetry can be observed at the 8 TeV LHC with 20
fb of data. If confirmed, it will be the first experimental measurement
of the sign of the imaginary part of one-loop QCD amplitudes.Comment: 5 pages, 2 figure
NLO QCD corrections to five-jet production at LEP and the extraction of alpha_s(M_Z)
The highest exclusive jet multiplicity studied at LEP experiments is five. In
this paper we compute the next-to-leading order QCD corrections to e+e-
annihilation to five jets, essentially closing the (pure) perturbative QCD
studies of exclusive jetty final states at LEP. We compare fixed-order
perturbative results with ALEPH data. We estimate hadronization corrections to
five-jet observables using the event generator SHERPA, which employs the CKKW
procedure to combine a reliable perturbative treatment of high-multiplicity jet
final states with parton showers. We show that a competitive value of the
strong coupling constant alpha_s(M_Z) = 0.1156 +0.0041 -0.0034 can be extracted
from the distribution of the five-jet resolution parameter and the five-jet
rate at LEP1 and LEP2.Comment: 25 pages, 5 figures. Published version (3 references addded, 1
sentence rephrased
Automatic spin-entangled decays of heavy resonances in Monte Carlo simulations
We present a general method that allows one to decay narrow resonances in Les
Houches Monte Carlo events in an efficient and accurate way. The procedure
preserves both spin correlation and finite width effects to a very good
accuracy, and is therefore particularly suited for the decay of resonances in
production events generated at next-to-leading-order accuracy. The method is
implemented as a generic tool in the MadGraph framework, giving access to a
very large set of possible applications. We illustrate the validity of the
method and the code by applying it to the case of single top and top quark pair
production, and show its capabilities on the case of top quark pair production
in association with a Higgs boson.Comment: 17 pages, 6 figures, published versio
Enhancing the ttH signal through top-quark spin polarization effects at the LHC
We compare the impact of top-quark spin polarization effects in Higgs boson
production in association with top-quark pairs and in corresponding backgrounds
at the LHC. Because of the spin-zero nature of the Higgs boson, one expects, in
the chiral limit for the top quarks, a substantial complementarity in
spin correlations for a Higgs decaying into fermions/gauge-bosons and
spin correlations for the corresponding irreducible backgrounds. Although top mass effects in production are in
general dominant, and seriously spoil the chiral-limit expectations, one can
find observables that capture the angular spin correlations and can
help in separating the signal from irreducible backgrounds. In particular, we
show that, for both and , taking into account
spin correlations in production and irreducible
backgrounds could appreciably improve the LHC sensitivity to the
channel.Comment: 18 pages, 9 figures; implementation of cuts corrected in figures 7-
DNA-Based asymmetric catalysis as a synthetic tool
De helische structuur van DNA heeft altijd al aantrekkingskracht gehad op chemici. In onze groep hebben we DNA gebruikt om een enantioselectieve katalysator te ontwikkelen. Dit concept is gebaseerd op een achiraal metaal complex dat kan binden aan DNA. Hierdoor wordt het beïnvloed door de chirale omgeving die door het DNA gevormd wordt en die kan worden overgedragen op verschillende asymmetrisch gekatalyseerde reacties zoals de Diels-Alder reactie, Michael additie, Friedel-Crafts alkylering en meer recent de syn-hydratie reactie.
In dit proefschrift wordt een vervolgstudie beschreven waarin het gebruik van DNA-gebaseerde katalyse verder uit gewerkt wordt voor het gebruik in synthetisch interessante reacties. Het onderzoek was gericht op twee gebieden, namelijk, 1) optimalisatie van de reactiecondities met betrekking tot de reactieschaal en het recyclen van de DNA-koper katalysator, 2) de ontwikkeling van nieuwe reacties die hiervoor onbekend of moeilijk uit te voeren waren.
The helical structure of DNA has always attracted special attention from chemist. In our group a concept was developed in which DNA is used in order to obtain enantioselective catalysis. This concept is based on an achiral metal complex which can bind non-covalently to the DNA. The helicity of the DNA is hereby transferred to the metal complex, which can be subsequently transferred onto a variety of asymmetrically catalyzed reactions, like the Diels-Alder reaction, the Michael addition, the Friedel-Crafts alkylation and more recently the syn-hydration reaction.
In this thesis, a follow-up investigation on the use of this concept in synthetically interesting reactions will be discussed. The research was focused in two directions. First the optimization of the reaction conditions in order to improve the scale of the reactions and the recycling of the catalyst after use. Secondly, the development of new reactions which were unknown or hard to perform, prior to this research.
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