A
bstract
We present precise predictions for four-lepton plus jets production at the LHC obtained within the fully automated S
herpa
+ O
pen
L
oops
framework. Off-shell intermediate vector bosons and ...related interferences are consistently included using the complex-mass scheme. Four-lepton plus 0- and 1-jet final states are described at NLO accuracy, and the precision of the simulation is further increased by squared quark-loop NNLO contributions in the gg → 4
ℓ
, gg → 4
ℓ
+ g, g
q
→ 4
ℓ
+
q
, and
→ 4
ℓ
+ g channels. These NLO and NNLO contributions are matched to the S
herpa
parton shower, and the 0- and 1-jet final states are consistently merged using the M
eps
@N
lo
technique. Thanks to Sudakov resummation, the parton shower provides improved predictions and uncertainty estimates for exclusive observables. This is important when jet vetoes or jet bins are used to separate four-lepton final states arising from Higgs decays, diboson production, and top-pair production. Detailed predictions are presented for the Atlas and C
ms
H → WW
*
analyses at 8 TeV in the 0- and 1-jet bins. Assessing renormalisation-, factorisation- and resummationscale uncertainties, which reflect also unknown subleading Sudakov logarithms in jet bins, we find that residual perturbative uncertainties are as small as a few percent.
We compare different procedures for combining fixed-order tree-level matrix-element generators with parton showers. We use the case of W-production at the Tevatron and the LHC to compare different ...implementations of the so-called CKKW and MLM schemes using different matrix-element generators and different parton cascades. We find that although similar results are obtained in all cases, there are important differences.
A
bstract
The data taken in Run II at the Large Hadron Collider have started to probe Higgs boson production at high transverse momentum. Future data will provide a large sample of events with ...boosted Higgs boson topologies, allowing for a detailed understanding of electroweak Higgs boson plus two-jet production, and in particular the vector-boson fusion mode (VBF). We perform a detailed comparison of precision calculations for Higgs boson production in this channel, with particular emphasis on large Higgs boson transverse momenta, and on the jet radius dependence of the cross section. We study fixed-order predictions at next-to-leading order and next-to-next-to-leading order QCD, and compare the results to NLO plus parton shower (NLOPS) matched calculations. The impact of the NNLO corrections on the central predictions is mild, with inclusive scale uncertainties of the order of a few percent, which can increase with the imposition of kinematic cuts. We find good agreement between the fixed-order and matched calculations in non-Sudakov regions, and the various NLOPS predictions also agree well in the Sudakov regime. We analyze backgrounds to VBF Higgs boson production stemming from associated production, and from gluon-gluon fusion. At high Higgs boson transverse momenta, the ∆
y
jj
and/or
m
jj
cuts typically used to enhance the VBF signal over background lead to a reduced efficiency. We examine this effect as a function of the jet radius and using different definitions of the tagging jets. QCD radiative corrections increase for all Higgs production modes with increasing Higgs boson
p
T
, but the proportionately larger increase in the gluon fusion channel results in a decrease of the gluon-gluon fusion background to electroweak Higgs plus two jet production upon requiring exclusive two-jet topologies. We study this effect in detail and contrast in particular a central jet veto with a global jet multiplicity requirement.
We present theoretical predictions for the production of top-quark pairs with up to three jets at the next-to leading order in perturbative QCD. The relevant calculations are performed with
Sherpa
...and
OpenLoops
. To address the issue of scale choices and related uncertainties in the presence of multiple scales, we compare results obtained with the standard scale
H
T
/
2
at fixed order and the M
i
NLO procedure. Analyzing various cross sections and distributions for
t
t
¯
+
0
,
1
,
2
,
3
jets at the 13 TeV LHC we find a remarkable overall agreement between fixed-order and M
i
NLO results. The differences are typically below the respective factor-two scale variations, suggesting that for all considered jet multiplicities missing higher-order effects should not exceed the ten percent level.
Ntuples for NLO events at hadron colliders Bern, Z.; Dixon, L.J.; Febres Cordero, F. ...
Computer physics communications,
05/2014, Letnik:
185, Številka:
5
Journal Article
Recenzirano
Odprti dostop
We present an event-file format for the dissemination of next-to-leading-order (NLO) predictions for QCD processes at hadron colliders. The files contain all information required to compute generic ...jet-based infrared-safe observables at fixed order (without showering or hadronization), and to recompute observables with different factorization and renormalization scales. The files also make it possible to evaluate cross sections and distributions with different parton distribution functions. This in turn makes it possible to estimate uncertainties in NLO predictions of a wide variety of observables without recomputing the short-distance matrix elements. The event files allow a user to choose among a wide range of commonly-used jet algorithms and jet-size parameters.
We provide event files for a W or Z boson accompanied by up to four jets, and for pure-jet events with up to four jets. The files are for the Large Hadron Collider with a center of mass energy of 7 or 8 TeV.
A C++ library along with a Python interface for handling these files is also provided and described in this article. The library allows a user to read the event files and recompute observables transparently for different pdf sets and factorization and renormalization scales.
Program title: nTupleReader
Catalogue identifier: AESC_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AESC_v1_0.html
Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland
Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html
No. of lines in distributed program, including test data, etc.: 62761
No. of bytes in distributed program, including test data, etc.: 442886
Distribution format: tar.gz
Programming language: C++ with Python interface.
Computer: Workstations.
Operating system: Linux, MacOS.
RAM: Varying bytes
Classification: 11.1, 11.5.
External routines: ROOT, LHAPDF
Nature of problem:
NLO QCD predictions for vector boson + jets and jet processes for generic observables.
Solution method:
Event files containing all information required to compute generic jet-based infrared-safe observables at fixed order and to recompute observables with different factorization and renormalization scales are provided. The library provides an interface to access the information in these files.
Running time:
The runtime scales linearly with the file size.
We present the cross sections for production of up to four jets at the Large Hadron Collider, at next-to-leading order in the QCD coupling. We use the BLACKHAT library in conjunction with SHERPA and ...a recently developed algorithm for assembling primitive amplitudes into color-dressed amplitudes. We adopt the cuts used by ATLAS in their study of multijet events in pp collisions at √s=7 TeV. We include estimates of nonperturbative corrections and compare to ATLAS data. We store intermediate results in a framework that allows the inexpensive computation of additional results for different choices of scale or parton distributions.
Signatures with an electroweak vector boson and many jets play a crucial role at the Large Hadron Collider, both in the measurement of Standard-Model parameters and in searches for new physics. ...Precise predictions for these multiscale processes are therefore indispensable. We present next-to-leading order QCD predictions for W±/Z+jets at s=13 TeV, including up to five/four jets in the final state. All production channels are included, and leptonic decays of the vector bosons are considered at the amplitude level. We assess theoretical uncertainties arising from renormalization- and factorization-scale dependence by considering fixed-order dynamical scales based on the HT variable as well as on the MiNLO procedure. We also explore uncertainties associated with different choices of parton-distribution functions. We provide event samples that can be explored through publicly available n-tuple sets, generated with BlackHat in combination with Sherpa.
Next-to-leading order W + 5 -jet production at the LHC Bern, Z.; Dixon, L. J.; Febres Cordero, F. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
07/2013, Letnik:
88, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present next-to-leading order QCD predictions for the total cross section and for a comprehensive set of transverse-momentum distributions in W + 5-jet production at the Large Hadron Collider. We ...neglect the small contributions from subleading-color virtual terms, top quarks, and some terms containing four quark pairs. We also present ratios of total cross sections, and use them to obtain an extrapolation formula to an even larger number of jets. We include the decay of the W boson into leptons. This is the first such computation with six final-state vector bosons or jets. We use BLACKHAT together with sherpa to carry out the computation.
We present an update of the Binoth Les Houches Accord (BLHA) to standardise the interface between Monte Carlo programs and codes providing one-loop matrix elements.
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