A standard file format is proposed to store process and event information, primarily output from parton-level event generators for further use by general-purpose ones. The information content is ...identical with what was already defined by the Les Houches Accord five years ago, but then in terms of Fortran commonblocks. This information is embedded in a minimal XML-style structure, for clarity and to simplify parsing.
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.
We propose four simple event-shape variables for semi-inclusive e.sup.+e.sup.- → 4-jet events. The observables and cuts are designed to be especially sensitive to subleading aspects of the event ...structure, and allow to test the reliability of phenomenological QCD models in greater detail. Three of them, θ.sub.14, θ.sup.*, and c.sup.(1/5).sub.2, focus on soft emissions off 3-jet topologies with a small opening angle, for which coherence effects beyond the leading QCD dipole pattern are expected to be enhanced. A complementary variable, M.sup.2.sub.L/M.sup.2.sub.H, measures the ratio of the hemisphere masses in 4-jet events with a compressed scale hierarchy (Durham y.sub.23 - y.sub.34), for which subleading 1 → 3 splitting effects are expected to be enhanced. We consider several different parton-shower models, spanning both conventional and dipole/antenna ones, all tuned to the same e.sup.+e.sup.- reference data, and show that a measurement of the proposed observables would allow for additional significant discriminating power between the models.
A study of QCD coherence is presented based on a sample of about 397,000
e
+
e
-
hadronic annihilation events collected at
s
=
91
GeV with the OPAL detector at LEP. The study is based on four ...recently proposed observables that are sensitive to coherence effects in the perturbative regime. The measurement of these observables is presented, along with a comparison with the predictions of different parton shower models. The models include both conventional parton shower models and dipole antenna models. Different ordering variables are used to investigate their influence on the predictions.
A study of QCD coherence is presented based on a sample of about 397,000 e+e- hadronic annihilation events collected at √s = 91 GeV with the OPAL detector at LEP. The study is based on four recently ...proposed observables that are sensitive to coherence effects in the perturbative regime. The measurement of these observables is presented, along with a comparison with the predictions of different parton shower models. The models include both conventional parton shower models and dipole antenna models. Different ordering variables are used to investigate their influence on the predictions.
Herwig++ physics and manual Bähr, Manuel; Gieseke, Stefan; Gigg, Martyn A. ...
The European physical journal. C, Particles and fields,
12/2008, Letnik:
58, Številka:
4
Journal Article
Recenzirano
Odprti dostop
In this paper we describe
version 2.2, a general-purpose Monte Carlo event generator for the simulation of hard lepton-lepton and hadron-hadron collisions. A number of important hard scattering ...processes are available, together with an interface via the Les Houches Accord to specialized matrix element generators for additional processes. The simulation of Beyond the Standard Model (BSM) physics includes a range of models and allows new models to be added by encoding the Feynman rules of the model. The parton-shower approach is used to simulate initial- and final-state QCD radiation, including colour coherence effects, with special emphasis on the correct description of radiation from heavy particles. The underlying event is simulated using an eikonal multiple parton-parton scattering model. The formation of hadrons from the quarks and gluons produced in the parton shower is described using the cluster hadronization model. Hadron decays are simulated using matrix elements, where possible including spin correlations and off-shell effects.
A
bstract
We calculate the process
pp
→
W
+
W
−
→
e
+
ν
e
μ
−
ν
¯
μ
at NLO QCD, including also effective field theory (EFT) operators mediating the
ggW
+
W
−
interaction, which first occur at ...dimension eight. We further combine the NLO and EFT matrix elements produced by G
o
S
am
with the H
erwig
7/M
atchbox
framework, which offers the possibility to study the impact of a parton shower. We assess the effects of the anomalous couplings by comparing them to top-mass effects as well as uncertainties related to variations of the renormalisation, factorisation and hard shower scales.
A new model of color reconnection in the Monte Carlo generator Herwig 7 is presented. It is based on the minimization of a boost-invariant distance of the parton system, where all partons have ...momentum as well as spacetime position assigned. We test the influence of both types of variables, namely the rapidity span and transverse distance, on the actual need to reconnect the system to better describe soft physics measurements. We find reasonable agreement with the data and conclude that spacetime topology of the event can be useful for hadron collision modeling.
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