3,571 research outputs found
Electron-Positron colliders
An electron-positron linear collider in the energy range between 500 and 1000
GeV is of crucial importance to precisely test the Standard Model and to
explore the physics beyond it. The physics program is complementary to that of
the Large Hadron Collider. Some of the main physics goals and the expected
accuracies of the anticipated measurements at such a linear collider are
discussed. A short review of the different collider designs presently under
study is given including possible upgrade paths to the multi-TeV region.
Finally a framework is presented within which the realisation of such a project
could be achieved as a global international project.Comment: 14 pages, 16 figures, Proceedings of the XX International Symposium
on Lepton and Photon Interactions at High Energies, Rome, Italy, 23-28 July,
200
A Simple Non-Markovian Computational Model of the Statistics of Soccer Leagues: Emergence and Scaling effects
We propose a novel algorithm that outputs the final standings of a soccer
league, based on a simple dynamics that mimics a soccer tournament. In our
model, a team is created with a defined potential(ability) which is updated
during the tournament according to the results of previous games. The updated
potential modifies a teams' future winning/losing probabilities. We show that
this evolutionary game is able to reproduce the statistical properties of final
standings of actual editions of the Brazilian tournament (Brasileir\~{a}o).
However, other leagues such as the Italian and the Spanish tournaments have
notoriously non-Gaussian traces and cannot be straightforwardly reproduced by
this evolutionary non-Markovian model. A complete understanding of these
phenomena deserves much more attention, but we suggest a simple explanation
based on data collected in Brazil: Here several teams were crowned champion in
previous editions corroborating that the champion typically emerges from random
fluctuations that partly preserves the gaussian traces during the tournament.
On the other hand, in the Italian and Spanish leagues only a few teams in
recent history have won their league tournaments. These leagues are based on
more robust and hierarchical structures established even before the beginning
of the tournament. For the sake of completeness, we also elaborate a totally
Gaussian model (which equalizes the winning, drawing, and losing probabilities)
and we show that the scores of the "Brasileir\~{a}o" cannot be reproduced. Such
aspects stress that evolutionary aspects are not superfluous in our modeling.
Finally, we analyse the distortions of our model in situations where a large
number of teams is considered, showing the existence of a transition from a
single to a double peaked histogram of the final classification scores. An
interesting scaling is presented for different sized tournaments.Comment: 18 pages, 9 figure
Characterization of the complex ion dynamics in lithium silicate glasses via computer simulations
We present results of molecular dynamics simulations on lithium metasilicate
over a broad range of temperatures for which the silicate network is frozen in
but the lithium ions can still be equilibrated. The lithium dynamics is studied
via the analysis of different correlation functions. The activation energy for
the lithium mobility agrees very well with experimental data. The correlation
of the dynamics of adjacent ions is weak. At low temperatures the dynamics can
be separated into local vibrational dynamics and hopping events between
adjacent lithium sites. The derivative of the mean square displacement displays
several characteristic time regimes. They can be directly mapped onto
respective frequency regimes for the conductivity. In particular it is possible
to identify time regimes dominated by localized dynamics and long-range
dynamics, respectively. The question of time-temperature superposition is
discussed for the mean square displacement and the incoherent scattering
function.Comment: to be published in Phys. Chem. Chem. Phy
Contributions to the mixed-alkali effect in molecular dynamics simulations of alkali silicate glasses
The mixed-alkali effect on the cation dynamics in silicate glasses is
analyzed via molecular dynamics simulations. Observations suggest a description
of the dynamics in terms of stable sites mostly specific to one ionic species.
As main contributions to the mixed--alkali slowdown longer residence times and
an increased probability of correlated backjumps are identified. The slowdown
is related to the limited accessibility of foreign sites. The mismatch
experienced in a foreign site is stronger and more retarding for the larger
ions, the smaller ions can be temporarily accommodated. Also correlations
between unlike as well as like cations are demonstrated that support
cooperative behavior.Comment: 10 pages, 12 figures, 1 table, revtex4, submitted to Phys. Rev.
CERN and the future of particle physics
This paper presents CERN and its current scientific programme and outlines options for high-energy colliders at the energy frontier for the years to come. The immediate plans include the exploitation of the LHC at its design
luminosity and energy as well as upgrades to the LHC and its injectors. This may be followed by a linear electron-positron collider, based on the technology being developed by the Compact Linear Collider and by the International Linear Collider, or by a high-energy electron-proton machine, the LHeC. This contribution describes the past, present and future directions, all of which have a unique value to add to experimental particle physics, and concludes by outlining key messages for the way forward
Deep-Elastic pp Scattering at LHC from Low-x Gluons
Deep-elastic pp scattering at c.m. energy 14 TeV at LHC in the momentum
transfer range 4 GeV*2 < |t| < 10 GeV*2 is planned to be measured by the TOTEM
group. We study this process in a model where the deep-elastic scattering is
due to a single hard collision of a valence quark from one proton with a
valence quark from the other proton. The hard collision originates from the
low-x gluon cloud around one valence quark interacting with that of the other.
The low-x gluon cloud can be identified as color glass condensate and has size
~0.3 F. Our prediction is that pp differential cross section in the large |t|
region decreases smoothly as momentum transfer increases. This is in contrast
to the prediction of pp differential cross section with visible oscillations
and smaller cross sections by a large number of other models.Comment: 10 pages, including 4 figure
Local Properties of the Potential Energy Landscape of a Model Glass: Understanding the Low Temperature Anomalies
Though the existence of two-level systems (TLS) is widely accepted to explain
low temperature anomalies in the sound absorption, heat capacity, thermal
conductivity and other quantities, an exact description of their microscopic
nature is still lacking. We performed computer simulations for a binary
Lennard-Jones system, using a newly developed algorithm to locate double-well
potentials (DWP) and thus two-level systems on a systematic basis. We show that
the intrinsic limitations of computer simulations like finite time and finite
size problems do not hamper this analysis. We discuss how the DWP are embedded
in the total potential energy landscape. It turns out that most DWP are
connected to the dynamics of the smaller particles and that these DWP are
rather localized. However, DWP related to the larger particles are more
collective
Particle rearrangements during transitions between local minima of the potential energy landscape of a supercooled Lennard-Jones liquid
The potential energy landscape (PEL) of supercooled binary Lennard-Jones
(BLJ) mixtures exhibits local minima, or inherent structures (IS), which are
organized into meta-basins (MB). We study the particle rearrangements related
to transitions between both successive IS and successive MB for a small 80:20
BLJ system near the mode-coupling temperature T_MCT. The analysis includes the
displacements of individual particles, the localization of the rearrangements
and the relevance of string-like motion. We find that the particle
rearrangements during IS and MB transitions do not change significantly at
T_MCT. Further, it is demonstrated that IS and MB dynamics are spatially
heterogeneous and facilitated by string-like motion. To investigate the
mechanism of string-like motion, we follow the particle rearrangements during
suitable sequences of IS transitions. We find that most strings observed after
a series of transitions do not move coherently during a single transition, but
subunits of different sizes are active at different times. Several findings
suggest that the occurrence of a successful string enables the system to exit a
MB. Moreover, we show that the particle rearrangements during two consecutive
MB transitions are basically uncorrelated. Specifically, different groups of
particles are highly mobile during subsequent MB transitions. Finally, the
relation between the features of the PEL and the relaxation processes in
supercooled liquids is discussed.Comment: 13 pages, 10 figure
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