177 research outputs found
Monte Carlo based studies of a polarized positron source for International Linear Collider (ILC)
The full exploitation of the physics potential of an International Linear
Collider (ILC) requires the development of a polarized positron beam. New
concepts of polarized positron sources are based on the development of
circularly polarized photon sources. The polarized photons create
electron-positron pairs in a thin target and transfer their polarization state
to the outgoing leptons. To achieve a high level of positron polarization the
understanding of the production mechanisms in the target is crucial. Therefore
a general framework for the simulation of polarized processes with GEANT4 is
under development. In this contribution the current status of the project and
its application to a study of the positron production process for the ILC is
presented.Comment: 5 pages, to appear in the proceedings of 10th International Workshop
on Advanced Computing and Analysis Techniques in Physics Research (ACAT 05),
Zeuthen, Germany, 22-27 May 2005. Submitted to Nucl.Instrum.Met
Solving the Train Dispatching Problem in Large Networks by Column Generation
Disruptions in the operational flow of rail traffic can lead to conflicts
between train movements, such that a scheduled timetable can no longer be
realised. This is where dispatching is applied, existing conflicts are resolved
and a dispatching timetable is provided. In the process, train paths are varied
in their spatio-temporal course. This is called the train dispatching problem
(TDP), which consists of selecting conflict-free train paths with minimum
delay. Starting from a path-oriented formulation of the TDP, a binary linear
decision model is introduced. For each possible train path, a binary decision
variable indicates whether the train path is used by the request or not. Such a
train path is constructed from a set of predefined path parts (\profiles{})
within a time-space network. Instead of modelling pairwise conflicts, stronger
MIP formulation are achieved by a clique formulation. The combinatorics of
speed profiles and different departure times results in a large number of
possible train paths, so that the column generation method is used here. New
train paths within the pricing-problem can be calculated using shortest path
techniques. Here, the shadow prices of conflict cliques must be taken into
account. When constructing a new train path, it must be determined whether this
train path belongs to a clique or not. This problem is tackled by a MIP. The
methodology is tested on practical size instances from a dispatching area in
Germany. Numerical results show that the presented method achieves acceptable
computation times with good solution quality while meeting the requirements for
real-time dispatching.Comment: 12 pages, 4 figures, 2 table
Bunch by Bunch Feedback and Diagnostics at BESSY II
At the light source BESSY II new digital bunch bybunch feedback systems [1] have been put into operation in January 2013, replacing the existing analog as well as the obsolete digital systems. From the first days of operation the new system successfully suppresses transverse and longitudinal beam instabilities in wide range of machine parameters. The system offers also many new diagnostics opportunities. In this contribution first operational experience, the developed data analysis techniques and experimental data will be presente
Event generation at hadron colliders
Diese Arbeit befasst sich mit der Simulation von hochenergetischen Hadron-Kollisionsexperimenten, wie sie im Moment am Tevatron (Fermilab) durchgeführt werden und in naher Zukunft am Large Hadron Collider (LHC) am CERN zu erwarten sind. Für die Beschreibung dieser Experimente wird ein Algorithmus untersucht, der es ermöglicht, exakte Multijet-Matrixelemente auf Baumgraphenniveau in die Simulation einzubeziehen und so die Qualität der Vorhersage deutlich zu verbessern. Die Implementierung dieses Algorithmus in den Eventgenerator "SHERPA" und die Erweiterung des Parton Showers in diesem Programm ist das Hauptthema dieser Arbeit. Die Ergebnisse werden mit experimentellen Daten und mit anderen Simulationen verglichen.This work deals with the accurate simulation of high energy hadron-hadron-collision experiments, as they are currently performed at Fermilab Tevatron or as they are expected at the Large Hadron Collider at CERN. For a precise description of these experiments an algorithm is investigated, which enables the inclusion of exact multi-jet matrix elements in the simulation. The implementation of this algorithm in the event generator "SHERPA" and the extension of its parton shower is the main topic of this work. The results are compared with those of other simulation programs and with experimental data
GR@PPA 2.7 event generator for / collisions
The GR@PPA event generator has been updated to version 2.7. This distribution
provides event generators for ( or ) + jets ( 4 jets), +
jets ( 2 jets) and QCD multi-jet ( 4 jets) production processes at
and collisions, in addition to the four bottom quark
productions implemented in our previous work (GR@PPA\_4b). Also included are
the top-pair and top-pair + jet production processes, where the correlation
between the decay products are fully reproduced at the tree level. Namely,
processes up to seven-body productions can be simulated, based on ordinary
Feynman diagram calculations at the tree level. In this version, the GR@PPA
framework and the process dependent matrix-element routines are separately
provided. This makes it easier to add further new processes, and allows users
to make a choice of processes to implement. This version also has several new
features to handle complicated multi-body production processes. A systematic
way to combine many subprocesses to a single base-subprocess has been
introduced, and a new method has been adopted to calculate the color factors of
complicated QCD processes. They speed up the calculation significantly.Comment: 21 pages, no figur
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