145 research outputs found
Higgs production in association with bottom quarks
We study the production of a Higgs boson in association with bottom quarks in
hadronic collisions, and present phenomenological predictions relevant to the
13 TeV LHC. Our results are accurate to the next-to-leading order in QCD, and
matched to parton showers through the MC@NLO method; thus, they are fully
differential and based on unweighted events, which we shower by using both
Herwig++ and Pythia8. We perform the computation in both the four-flavour and
the five-flavour schemes, whose results we compare extensively at the level of
exclusive observables. In the case of the Higgs transverse momentum, we also
consider the analytically-resummed cross section up to the NNLO+NNLL accuracy.
In addition, we analyse at the effects of the
interference between the and gluon-fusion production modes.Comment: 33 pages, 17 figure
Recommended from our members
Large N expansion of q-deformed two-dimensional Yang-Mills theory and hecke algebras
We derive the q-deformation of the chiral Gross-Taylor holomorphic string
large N expansion of two dimensional SU(N) Yang-Mills theory. Delta functions
on symmetric group algebras are replaced by the corresponding objects
(canonical trace functions) for Hecke algebras. The role of the Schur-Weyl
duality between unitary groups and symmetric groups is now played by q-deformed
Schur-Weyl duality of quantum groups. The appearance of Euler characters of
configuration spaces of Riemann surfaces in the expansion persists. We discuss
the geometrical meaning of these formulae
Higgs pair production at the LHC with NLO and parton-shower effects
We present predictions for the SM-Higgs-pair production channels of relevance
at the LHC: gluon-gluon fusion, VBF, and top-pair, W, Z and single-top
associated production. All these results are at the NLO accuracy in QCD, and
matched to parton showers by means of the MC@NLO method; hence, they are fully
differential. With the exception of the gluon-gluon fusion process, for which a
special treatment is needed in order to improve upon the infinite-top-mass
limit, our predictions are obtained in a fully automatic way within the
publicly available MadGraph5_aMC@NLO framework. We show that for all channels
in general, and for gluon-gluon fusion and top-pair associated production in
particular, NLO corrections reduce the theoretical uncertainties, and are
needed in order to arrive at reliable predictions for total rates as well as
for distributions.Comment: 11 pages, 7 figures, version accepted for publication on PL
On the reduction of negative weights in MC@NLO-type matching procedures
We show how a careful analysis of the behaviour of a parton shower Monte
Carlo in the vicinity of the soft and collinear regions allows one to formulate
a modified MC@NLO-matching prescription that reduces the number of
negative-weight events with respect to that stemming from the standard MC@NLO
procedure. As a first practical application of such a prescription, that we dub
MC@NLO-, we have implemented it in the MadGraph5_aMC@NLO framework, by
employing the Pythia8 Monte Carlo. We present selected MC@NLO- results
at the 13 TeV LHC, and compare them with MC@NLO ones. We find that the former
predictions are consistent with the latter ones within the typical matching
systematics, and that the reduction of negative-weight events is significant.Comment: 44 pages, 13 figures; several minor text amendments and one figure
adde
A study of multi-jet production in association with an electroweak vector boson
Abstract: We consider the production of a single Z or W boson in association with jets at the LHC. We compute the corresponding cross sections by matching NLO QCD predictions with the Herwig++ and Pythia8 parton showers, and by merging all of the underlying matrix elements with up to two light partons at the Born level. We compare our results with several 7-TeV measurements by the ATLAS and CMS collaborations, and overall we find a good agreement between theory and data
NLO QCD corrections in Herwig++ with MC@NLO
We present the calculations necessary to obtain next-to-leading order QCD
precision with the Herwig++ event generator using the MC@NLO approach, and
implement them for all the processes that were previously available from
Fortran HERWIG with MC@NLO. We show a range of results comparing the two
implementations. With these calculations and recent developments in the
automatic generation of NLO matrix elements, it will be possible to obtain NLO
precision with Herwig++ for a much wider range of processesComment: 26 pages, 28 figure
The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
We discuss the theoretical bases that underpin the automation of the
computations of tree-level and next-to-leading order cross sections, of their
matching to parton shower simulations, and of the merging of matched samples
that differ by light-parton multiplicities. We present a computer program,
MadGraph5_aMC@NLO, capable of handling all these computations -- parton-level
fixed order, shower-matched, merged -- in a unified framework whose defining
features are flexibility, high level of parallelisation, and human intervention
limited to input physics quantities. We demonstrate the potential of the
program by presenting selected phenomenological applications relevant to the
LHC and to a 1-TeV collider. While next-to-leading order results are
restricted to QCD corrections to SM processes in the first public version, we
show that from the user viewpoint no changes have to be expected in the case of
corrections due to any given renormalisable Lagrangian, and that the
implementation of these are well under way.Comment: 158 pages, 27 figures; a few references have been adde
Matching NLO QCD computations with PYTHIA using MC@NLO
We present the matching between a next-to-leading order computation in QCD
and the PYTHIA parton shower Monte Carlo, according to the MC@NLO formalism. We
study the case of initial-state radiation, and consider in particular single
vector boson hadroproduction.Comment: 16 pages, 10 figures. Several comments and two figures have been
adde
- …