51 research outputs found
Probing collective effects in hadronisation with the extremes of the underlying event
We define a new set of observables to probe the structure of the underlying
event in hadron collisions. We use the conventional definition of the
`transverse region' in jet events and, for a fixed window in jet ,
propose to measure several discriminating quantities as a function of the level
of activity in the transverse region. The measurement of these observables in
LHC data would reveal whether, e.g., the properties of `low-UE' events are
compatible with equivalent measurements in collisions (jet
universality), and whether the scaling behaviour towards `high-UE' events
exhibits properties of non-trivial soft-QCD dynamics, such as colour
re-connections or other collective phenomena. We illustrate at
TeV that significant discriminatory power is obtained in comparisons between MC
models with varying treatments of collective effects, including Pythia 8, EPOS,
and Dipsy.Comment: 23 pages, 8 figure
A fundamental test of the Higgs Yukawa coupling at RHIC in A+A collisions
Searches for the intermediate boson, , the heavy quantum of the Weak
Interaction, via its semi-leptonic decay, , in the 1970's instead
discovered unexpectedly large hadron production at high , notably ,
which provided a huge background of from internal and external
conversions. Methods developed at the CERN ISR which led to the discovery of
direct-single- in 1974, later determined to be from the semi-leptonic
decay of charm which had not yet been discovered, were used by PHENIX at RHIC
to make precision measurements of heavy quark production in p-p and Au+Au
collisions, leading to the puzzle of apparent equal suppression of light and
heavy quarks in the QGP. If the Higgs mechanism gives mass to gauge bosons but
not to fermions, then a proposal that all 6 quarks are nearly massless in a
QGP, which would resolve the puzzle, can not be excluded. This proposal can be
tested with future measurements of heavy quark correlations in A+A collisionsComment: 12 pages, 16 figures, 26th Winter Workshop on Nuclear Dynamics, Ocho
Rios, Jamaica WI, January 2-9, 2010. Corrected citation of 1974 direct single
lepton discover
Large Transverse Momenta in Statistical Models of High Energy Interactions
The creation of particles with large transverse momenta in high energy
hadronic collisions is a long standing problem. The transition from small-
(soft) to hard- parton scattering `high-pt' events is rather smooth. In this
paper we apply the non-extensive statistical framework to calculate transverse
momentum distributions of long lived hadrons created at energies from low
(sqrt(s)~10 GeV) to the highest energies available in collider experiments
(sqrt(s)~2000 GeV). Satisfactory agreement with the experimental data is
achieved. The systematic increase of the non-extensivity parameter with energy
found can be understood as phenomenological evidence for the increased role of
long range correlations in the hadronization process.
Predictions concerning the rise of average transverse momenta up to the
highest cosmic ray energies are also given and discussed.Comment: 20 pages, 10 figure
Multiple Interactions and the Structure of Beam Remnants
Recent experimental data have established some of the basic features of
multiple interactions in hadron-hadron collisions. The emphasis is therefore
now shifting, to one of exploring more detailed aspects. Starting from a brief
review of the current situation, a next-generation model is developed, wherein
a detailed account is given of correlated flavour, colour, longitudinal and
transverse momentum distributions, encompassing both the partons initiating
perturbative interactions and the partons left in the beam remnants. Some of
the main features are illustrated for the Tevatron and the LHC.Comment: 69pp, 33 figure
PYTHIA 6.4 Physics and Manual
The PYTHIA program can be used to generate high-energy-physics `events', i.e.
sets of outgoing particles produced in the interactions between two incoming
particles. The objective is to provide as accurate as possible a representation
of event properties in a wide range of reactions, within and beyond the
Standard Model, with emphasis on those where strong interactions play a role,
directly or indirectly, and therefore multihadronic final states are produced.
The physics is then not understood well enough to give an exact description;
instead the program has to be based on a combination of analytical results and
various QCD-based models. This physics input is summarized here, for areas such
as hard subprocesses, initial- and final-state parton showers, underlying
events and beam remnants, fragmentation and decays, and much more. Furthermore,
extensive information is provided on all program elements: subroutines and
functions, switches and parameters, and particle and process data. This should
allow the user to tailor the generation task to the topics of interest.Comment: 576 pages, no figures, uses JHEP3.cls. The code and further
information may be found on the PYTHIA web page:
http://www.thep.lu.se/~torbjorn/Pythia.html Changes in version 2: Mistakenly
deleted section heading for "Physics Processes" reinserted, affecting section
numbering. Minor updates to take into account referee comments and new colour
reconnection option
Model-Independent Global Constraints on New Physics
Using effective-lagrangian techniques we perform a systematic survey of the
lowest-dimension effective interactions through which heavy physics might
manifest itself in present experiments. We do not restrict ourselves to special
classes of effective interactions (such as `oblique' corrections). We compute
the effects of these operators on all currently well-measured electroweak
observables, both at low energies and at the resonance, and perform a
global fit to their coefficients. Despite the fact that a great many operators
arise in our survey, we find that most are quite strongly bounded by the
current data. We use our survey to systematically identify those effective
interactions which are {\it not} well-bounded by the data -- these could very
well include large new-physics contributions. Our results may also be used to
efficiently confront specific models for new physics with the data, as we
illustrate with an example.Comment: plain TeX, 68 pages, 2 figures (postscript files appended),
McGill-93/12, NEIPH-93-008, OCIP/C-93-6, UQAM-PHE-93/08, UdeM-LPN-TH-93-15
Strange di-muon events at the panti p-collider
SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
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