45 research outputs found
Simulated NNLO for high-pT observables in vector boson + jets production at the LHC
We present a study of higher order QCD corrections beyond NLO to processes
with an electroweak vector boson, W or Z, in association with jets. We focus on
the regions of high transverse momenta of commonly used differential
distributions. We employ the LoopSim method to merge NLO samples of different
multiplicity obtained from MCFM and from BLACKHAT+SHERPA in order to compute
the dominant part of the NNLO corrections for high-pT observables. We find that
these corrections are indeed substantial for a number of experimentally
relevant observables. For other observables, they lead to significant reduction
of scale uncertainties.Comment: 16 pages, 8 figures; v2: expanded discussion in a few places, added
and corrected references, version accepted by Eur. Phys. J.
Small-x single-particle distributions in jets from the coherent branching formalism
We calculate single parton distributions inside quark and gluon jets within
the coherent branching formalism, which resums leading and next-to-leading
logarithmic contributions. This formalism is at the basis of the modified
leading logarithmic approximation (MLLA), and it conserves energy exactly. For
a wide preasymptotic range of the evolution variable Y=ln[E\theta/Q_0], we find
marked differences in the shape and norm of single parton distributions
calculated in the MLLA or in the coherent branching formalism, respectively.
For asymptotically large values Y>5-10, the difference in norm persists, while
differences in shape disappear. In this way, our numerical study delineates the
jet energy scale needed for a reliable application of both approaches. We also
study the dependence of the single parton distributions on the hadronization
scale Q_0 and on \Lambda_QCD, and we calculate within the coherent branching
formalism the identified quark and gluon distributions inside quark and gluon
jets.Comment: 23 pages, 12 figure
Saturation model of DIS : an update
We present the results of new fits to the recently extracted data on at
low with the GBW saturation model and its modification to cover high values
of . We find that the model stands the test of time and gives a good
description of the data with slightly modified parameters. All the essential
elements of the model, especially the saturation scale, are retained.Comment: 16 pages, 8 figures; v2: several textual changes and additions, Table
2 added, version accepted by JHEP; v3: misprint correcte
ZZ production at high transverse momenta beyond NLO QCD
We study the production of the four-lepton final state ,
predominantly produced by a pair of electroweak Z bosons, ZZ. Using the LoopSim
method, we merge NLO QCD results for ZZ and ZZ+jet and obtain approximate NNLO
predictions for ZZ production. The exact gluon-fusion loop-squared contribution
to the ZZ process is also included. On top of that, we add to our merged sample
the gluon-fusion ZZ+jet contributions from the gluon-gluon channel, which is
formally of N^3LO and provides approximate results at NLO for the gluon-fusion
mechanism. The predictions are obtained with the VBFNLO package and include the
leptonic decays of the Z bosons with all off-shell and spin-correlation
effects, as well as virtual photon contributions. We compare our predictions
with existing results for the total inclusive cross section at NNLO and find a
very good agreement. Then, we present results for differential distributions
for two experimental setups, one used in searches for anomalous triple gauge
boson couplings, the other in Higgs analyses in the four charged-lepton final
state channel. We find that the approximate NNLO corrections are large,
reaching up to 20% at high transverse momentum of the Z boson or the leading
lepton, and are not covered by the NLO scale uncertainties. Distributions of
the four-lepton invariant mass are, however, stable with respect to QCD
corrections at this order.Comment: 21 pages, 2 tables, 9 figure
QCD and Jets at Hadron Colliders
We review various aspects of jet physics in the context of hadron colliders.
We start by discussing the definitions and properties of jets and recent
development in this area. We then consider the question of factorization for
processes with jets, in particular for cases in which jets are produced in
special configurations, like for example in the region of forward rapidities.
We review numerous perturbative methods for calculating predictions for jet
processes, including the fixed-order calculations as well as various matching
and merging techniques. We also discuss the questions related to
non-perturbative effects and the role they play in precision jet studies. We
describe the status of calculations for processes with jet vetoes and we also
elaborate on production of jets in forward direction. Throughout the article,
we present selected comparisons between state-of-the-art theoretical
predictions and the data from the LHC.Comment: 77 pages, 37 figures; v2: text developments in several places,
references added, version published in Prog. Part. Nucl. Phys. 201
Single and double inclusive forward jet production at the LHC at = 7 and 13 TeV
We provide a description of the transverse momentum spectrum of single
inclusive forward jets produced at the LHC, at the center-of-mass energies of 7
and 13 TeV, using the high energy factorization (HEF) framework. We
subsequently study double inclusive forward jet production and, in particular,
we calculate contributions to azimuthal angle distributions coming from double
parton scattering. We also compare our results for double inclusive jet
production to those obtained with the Pythia Monte Carlo generator. This
comparison confirms that the HEF resummation acts like an initial state parton
shower. It also points towards the need to include final state radiation
effects in the HEF formalism.Comment: 14 pages, 5 figures, version accepted for PL