7,178 research outputs found
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
Remarks on the particle multiplicities at LHC energies
Recent ALICE data for the multiplicity distributions in the central rapidity
bins at LHC energies are compared with the results from two default versions of
the PYTHIA 8 generator. We find that, contrary to the earlier versions of
PYTHIA, the model overestimates the increase of average multiplicity with
energy. Tuning two of the model parameters one obtains reasonable agreement
with data. The dependence of the normalized moments of the distribution on the
rapidity bin width and on energy is also qualitatively correct.Comment: 6 pages, 1 figur
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
Status of ATLAS and Preparation for the Pb-Pb Run
The ATLAS experiment took its first beam data in September 2008 and is
actively preparing for the planned start of LHC collision data-taking in 2009.
This preparation includes hardware and software commissioning, as well as
calibration and cosmic data analysis. The status and performance of the ATLAS
detector will be discussed, with a view towards the Pb+Pb run expected in 2010.Comment: 8 pages, 14 figures, corrected typos, added references, figures
corrected for better legibility in B&W - To appear in the conference
proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
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
Semiclassical Nonconcentration near Hyperbolic Orbits
For a large class of semiclassical pseudodifferential operators, including
Schr\"odinger operators, , on compact
Riemannian manifolds, we give logarithmic lower bounds on the mass of
eigenfunctions outside neighbourhoods of generic closed hyperbolic orbits. More
precisely we show that if is a pseudodifferential operator which is
microlocally equal to the identity near the hyperbolic orbit and microlocally
zero away from the orbit, then This generalizes earlier
estimates of Colin de Verdi\`ere-Parisse \cite{CVP} obtained for a special
case, and of Burq-Zworski \cite{BZ} for real hyperbolic orbits.Comment: 45 pages, 5 figure
On the sign-imbalance of partition shapes
Let the sign of a standard Young tableau be the sign of the permutation you
get by reading it row by row from left to right, like a book. A conjecture by
Richard Stanley says that the sum of the signs of all SYTs with n squares is
2^[n/2]. We present a stronger theorem with a purely combinatorial proof using
the Robinson-Schensted correspondence and a new concept called chess tableaux.
We also prove a sharpening of another conjecture by Stanley concerning
weighted sums of squares of sign-imbalances. The proof is built on a remarkably
simple relation between the sign of a permutation and the signs of its
RS-corresponding tableaux.Comment: 12 pages. Better presentatio
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
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