We quantify uncertainties in the Monte Carlo simulation of inclusive and dijet final states, which arise from using the MCatNLO technique for matching next-to-leading order parton-level calculations ...and parton showers. We analyse a large variety of data from early measurements at the LHC. In regions of phase space where Sudakov logarithms dominate over high-energy effects, we observe that the main uncertainty can be ascribed to the free parameters of the parton shower. In complementary regions, the main uncertainty stems from the considerable freedom in the simulation of underlying events.
We review the physics basis, main features and use of general-purpose Monte Carlo event generators for the simulation of proton–proton collisions at the Large Hadron Collider. Topics included are: ...the generation of hard scattering matrix elements for processes of interest, at both leading and next-to-leading QCD perturbative order; their matching to approximate treatments of higher orders based on the showering approximation; the parton and dipole shower formulations; parton distribution functions for event generators; non-perturbative aspects such as soft QCD collisions, the underlying event and diffractive processes; the string and cluster models for hadron formation; the treatment of hadron and tau decays; the inclusion of QED radiation and beyond Standard Model processes. We describe the principal features of the
Ariadne, Herwig++,
Pythia 8 and
Sherpa generators, together with the Rivet and Professor validation and tuning tools, and discuss the physics philosophy behind the proper use of these generators and tools. This review is aimed at phenomenologists wishing to understand better how parton-level predictions are translated into hadron-level events as well as experimentalists seeking a deeper insight into the tools available for signal and background simulation at the LHC.
NLO matrix elements and truncated showers Höche, Stefan; Krauss, Frank; Schönherr, Marek ...
The journal of high energy physics,
08/2011, Letnik:
2011, Številka:
8
Journal Article
Recenzirano
Odprti dostop
In this publication, an algorithm is presented that combines the ME+PS approach to merge sequences of tree-level matrix elements into inclusive event samples
1
with the P
owheg
method, which ...combines exact next-to-leading order matrix element results with the parton shower
2
,
3
. It was developed in parallel to the ME
nlo
PS technique discussed in
4
and has been implemented in the event generator S
herpa
5
,
6
. The benefits of this approach are exemplified by some first predictions for a number of processes, namely the production of jets in
e
+
e
−
-annihilation, in deep-inelastic
ep
scattering, in association with single
W
,
Z
or Higgs bosons, and with vector boson pairs at hadron colliders.
For the first time, differential cross sections for the production of W bosons in conjunction with up to three jets, computed at next-to leading order in QCD and including parton shower corrections, ...are presented and compared to recent experimental data from the Large Hadron Collider.
Resonance-aware subtraction in the dipole method Höche, Stefan; Liebschner, Sebastian; Siegert, Frank
The European physical journal. C, Particles and fields,
09/2019, Letnik:
79, Številka:
9
Journal Article
Recenzirano
Odprti dostop
We present a technique for infrared subtraction in next-to-leading order QCD calculations that preserves the virtuality of resonant propagators. The approach is based on the pseudo-dipole subtraction ...method proposed by Catani and Seymour in the context of identified particle production. As the first applications, we compute the
e
+
e
-
→
W
+
W
-
b
b
¯
and
p
p
→
W
+
W
-
j
b
j
b
cross-section, which are both dominated by top-quark pair production above the threshold. We compare the efficiency of our approach with a calculation performed using the standard dipole subtraction technique.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Automating the Powheg method in Sherpa Höche, Stefan; Krauss, Frank; Schönherr, Marek ...
The journal of high energy physics,
04/2011, Letnik:
2011, Številka:
4
Journal Article
Recenzirano
Odprti dostop
A new implementation of the P
owheg
method
1
,
2
into the Monte-Carlo event generator S
herpa
3
,
4
is presented, focusing on processes with a simple colour structure. Results for a variety of ...reactions, namely
e
+
e
−
→ hadrons, deep-inelastic lepton-nucleon scattering, hadroproduction of single vector bosons and of vector boson pairs as well as the production of Higgs bosons in gluon fusion serve as test cases for the successful realisation. The algorithm is highly automated such that for other processes with simple colour topology only virtual matrix elements need to be provided.
We present differential cross sections for the production of top-quark pairs in conjunction with up to two jets, computed at next-to-leading order in perturbative QCD and consistently merged with a ...parton shower in the Sherpa+OpenLoops framework. Top quark decays including spin correlation effects are taken into account at leading order accuracy. The calculation yields a unified description of top-pair plus multi-jet production, and detailed results are presented for various key observables at the Large Hadron Collider. A large improvement with respect to the multi-jet merging approach at leading order is found for the total transverse energy spectrum, which plays a prominent role in searches for physics beyond the Standard Model.
QCD splittings are among the most fundamental theory concepts at the LHC. We show how they can be studied systematically with the help of invertible neural networks. These networks work with sub-jet ...information to extract fundamental parameters from jet samples. Our approach expands the LEP measurements of QCD Casimirs to a systematic test of QCD properties based on low-level jet observables. Starting with an toy example we study the effect of the full shower, hadronization, and detector effects in detail.
Triple gauge boson hadroproduction, in particular the production of three W-bosons at the LHC, is considered at next-to leading order accuracy in QCD. The NLO matrix elements are combined with parton ...showers. Multijet merging is invoked such that NLO matrix elements with one additional jet are also included. The studies here incorporate both the signal and all relevant backgrounds for V H production with the subsequent decay of the Higgs boson into W– or τ–- pairs. They have been performed using SHERPA+OPENLOOPS in combination with COLLIER.
Many highly developed Monte Carlo tools for the evaluation of cross sections based on tree matrix elements exist and are used by experimental collaborations in high energy physics. As the evaluation ...of one-loop matrix elements has recently been undergoing enormous progress, the combination of one-loop matrix elements with existing Monte Carlo tools is on the horizon. This would lead to phenomenological predictions at the next-to-leading order level. This note summarises the discussion of the next-to-leading order multi-leg (NLM) working group on this issue which has been taking place during the workshop on Physics at TeV Colliders at Les Houches, France, in June 2009. The result is a proposal for a standard interface between Monte Carlo tools and one-loop matrix element programs.
Dedicated to the memory of, and in tribute to, Thomas Binoth, who led the effort to develop this proposal for Les Houches 2009. Thomas led the discussions, set up the subgroups, collected the contributions, and wrote and edited this paper. He made a promise that the paper would be on the arXiv the first week of January, and we are faithfully fulfilling his promise. In his honour, we would like to call this the Binoth Les Houches Accord.
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