264 research outputs found
Monte Carlo Generators
The structure of events in high-energy collisions is complex and not
predictable from first principles. Event generators allow the problem to be
subdivided into more manageable pieces, some of which can be described from
first principles, while others need to be based on appropriate models with
parameters tuned to data. In these lectures we provide an overview, discuss how
matrix elements are used, introduce the machinery for initial- and final-state
parton showers, explain how matrix elements and parton showers can be combined
for optimal accuracy, introduce the concept of multiple parton--parton
interactions, comment briefly on the hadronization issue, and provide an
outlook for the future.Comment: 23 pages, lectures presented at the 2006 European School of
High-Energy Physics, Aronsborg, Sweden, 18 June -- 1 July 200
PYTHIA 8 Status Report
Pythia 8, the C++ rewrite of the commonly-used Pythia event generator, is now
available in a first full-fledged version 8.1. The older Pythia 6.4 generator
in Fortran 77 is still maintained, for now, but users are strongly recommended
to try out and move to the new version as soon as feasible.Comment: 5 pages, to appear in the proceedings of the HERA and the LHC
workshop, 26--30 May 2008, CER
Status and developments of event generators
Event generators play a crucial role in the exploration of LHC physics. This
presentation summarizes news and plans for the three general-purpose pp
generators HERWIG, PYTHIA and SHERPA, as well as briefer notes on a few other
generators. Common themes, such as the matching and merging between matrix
elements and parton showers, are highlighted. Other topics include a historical
introduction, from the Lund perspective, and comments on the role of MCnet.Comment: 22 pages, 9 figures, presented at the Fourth Annual Large Hadron
Collider Physics Conference (LHCP2016), 13--18 June 2016, Lund, Swede
Collective Effects: the viewpoint of HEP MC codes
Collective effects are observed in high-multiplicity pp events, similar to
the signals traditionally attributed to the formation of a Quark Gluon Plasma
in heavy ion collisions. In core--corona models it is assumed that a partial
plasma formation is indeed possible also in pp, but here the focus is on
several recent models that attempt to explain pp data without invoking plasma
formation. These attempts are partly successful, but there is still not a
unified framework.Comment: 8 pages, presented at XXVIIth International Conference on
Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2018
QCD Interconnection Effects
Heavy objects like the W, Z and t are short-lived compared with typical
hadronization times. When pairs of such particles are produced, the subsequent
hadronic decay systems may therefore become interconnected. We study such
potential effects at Linear Collider energies.Comment: 1+7 pages, 6 eps figures, to appear in the Proceedings of the
Workshop on the development of future linear electron-positron colliders for
particle physics studies and for research using free electon lasers, Lund,
Sweden, 23-26 September 199
Colour reconnection and its effects on precise measurements at the LHC
There are experimental evidence for the occurrence of colour reconnection,
but the mechanisms involved are far from understood. Previous reconnection
studies are briefly summarized, and some potential implications for LHC physics
are outlined.Comment: 8 pages, 1 figure, to appear in the proceedings of the XLIII
International Symposium on Multiparticle Dynamics (ISMD13), Chicago, USA, 15
-- 20 September 201
Monte Carlo Tools
Given the current landscape in experimental high-energy physics, these
lectures are focused on applications of event generators for hadron colliders
like the Tevatron and LHC. Section 2 contains a first overview of the physics
picture and the generator landscape. Thereafter section 3 describes the usage
of matrix elements, section 4 the important topics of initial- and final-state
showers, and section 5 how showers can be matched to different hard processes.
The issue of multiparton interactions and their role in mimimum-bias and
underlying-event physics is introduced in section 6, followed by some comments
on hadronization in section 7. The article concludes with an outlook on the
ongoing generator-development work in section 8.Comment: 27 pages, to appear in the proceedings of the 65th Scottish
Universities Summer School in Physics: LHC Physics, St Andrews, 16 - 29
August 200
Jet Production by Virtual Photons
The production of jets is studied in collisions of virtual photons, gamma*-p
and gamma*-gamma*, specifically for applications at HERA and LEP2. Photon flux
factors are convoluted with matrix elements involving either direct or resolved
photons and, for the latter, with parton distributions of the photon. Special
emphasis is put on the range of uncertainty in the modeling of the resolved
component. The resulting model is compared with existing data.Comment: 1+36 pages, LaTeX2e, 63 eps figures, submitted to Eur. Phys. J.
Multiparton Interactions with an x-dependent Proton Size
Theoretical arguments, supported by other indirect evidence, suggest that the
wave function of high-x partons should be narrower than that of low-x ones. In
this article, we present a modification to the variable impact parameter
framework of Pythia 8 to model this effect. In particular, a Gaussian hadronic
matter profile is introduced, with a width dependent on the x value of the
constituent being probed. Results are compared against the default single- and
double-Gaussian profiles, as well as an intermediate overlap function
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