1,183 research outputs found
Tuning of MC generator MPI models
MC models of multiple partonic scattering inevitably introduce many free
parameters, either fundamental to the models or from their integration with MC
treatments of primary-scattering evolution. This non-perturbative and
non-factorisable physics in particular cannot currently be constrained from
theoretical principles, and hence parameter optimisation against experimental
data is required. This process is commonly referred to as MC tuning. We
summarise the principles, problems and history of MC tuning, and the
still-evolving modern approach to both model optimisation and estimation of
modelling uncertainties.Comment: Contributed chapter to "Multiple Parton Interactions at the LHC",
World Scientific 201
Simulation of vector boson plus many jet final states at the high luminosity LHC
We present a novel event generation framework for the efficient simulation of
vector boson plus multi-jet backgrounds at the high-luminosity LHC and at
possible future hadron colliders. MPI parallelization of parton-level and
particle-level event generation and storage of parton-level event information
using the HDF5 data format allow us to obtain leading-order merged Monte-Carlo
predictions with up to nine jets in the final state. The parton-level event
samples generated in this manner correspond to an integrated luminosity of
3ab-1 and are made publicly available for future phenomenological studies.Comment: 10 pages, 8 figures, 5 table
Heterogeneous diffusion in comb and fractal grid structures
We give an exact analytical results for diffusion with a power-law position
dependent diffusion coefficient along the main channel (backbone) on a comb and
grid comb structures. For the mean square displacement along the backbone of
the comb we obtain behavior , where
is the power-law exponent of the position dependent diffusion
coefficient . Depending on the value of we
observe different regimes, from anomalous subdiffusion, superdiffusion, and
hyperdiffusion. For the case of the fractal grid we observe the mean square
displacement, which depends on the fractal dimension of the structure of the
backbones, i.e., , where
is the fractal dimension of the backbones structure. The reduced
probability distribution functions for both cases are obtained by help of the
Fox -functions
Content-Aware DataGuides for Indexing Large Collections of XML Documents
XML is well-suited for modelling structured data with
textual content. However, most indexing approaches perform
structure and content matching independently, combining
the retrieved path and keyword occurrences in a third
step. This paper shows that retrieval in XML documents can
be accelerated significantly by processing text and structure
simultaneously during all retrieval phases. To this end,
the Content-Aware DataGuide (CADG) enhances the wellknown
DataGuide with (1) simultaneous keyword and path
matching and (2) a precomputed content/structure join. Extensive
experiments prove the CADG to be 50-90% faster
than the DataGuide for various sorts of query and document,
including difficult cases such as poorly structured
queries and recursive document paths. A new query classification
scheme identifies precise query characteristics with
a predominant influence on the performance of the individual
indices. The experiments show that the CADG is applicable
to many real-world applications, in particular large
collections of heterogeneously structured XML documents
Constraining Leptonic Flavour Model Parameters at Colliders and Beyond
The observed pattern of mixing in the neutrino sector may be explained by the
presence of a non-Abelian, discrete flavour symmetry broken into residual
subgroups at low energies. Many flavour models require the presence of Standard
Model singlet scalars which can promptly decay to charged leptons in a
flavour-violating manner. We constrain the model parameters of a generic
leptonic flavour model using a synergy of experimental data including limits
from charged lepton flavour conversion, an 8 TeV collider analysis and
constraints from the anomalous magnetic moment of the muon. The most powerful
constraints derive from the MEG collaborations' limit on Br and the reinterpretation of an 8 TeV ATLAS search for anomalous
productions of multi-leptonic final states. We quantify the exclusionary power
of each of these experiments and identify regions where the constraints from
collider and MEG experimental data are complementary.Comment: v1: 28 + 9 pages, 8 figures. v2: 30 + 10 pages, 10 figures. v2
consistent with JHEP accepted version where further discussion of results and
several more references were adde
Monte Carlo event generator validation and tuning for the LHC
We summarise the motivation for, and the status of, the tools developed by
CEDAR/MCnet for validating and tuning Monte Carlo event generators for the LHC
against data from previous colliders. We then present selected preliminary
results from studies of event shapes and hadronisation observables from e+e-
colliders, and of minimum bias and underlying event observables from the
Tevatron, and comment on the approach needed with early LHC data to best
exploit the potential for new physics discoveries at the LHC in the next few
years.Comment: Prepared for Proceedings of XII Advanced Computing and Analysis
Techniques in Physics Research, November 3-7 2008, Erice, Ital
New developments in event generator tuning techniques
Data analyses in hadron collider physics depend on background simulations
performed by Monte Carlo (MC) event generators. However, calculational
limitations and non-perturbative effects require approximate models with
adjustable parameters. In fact, we need to simultaneously tune many
phenomenological parameters in a high-dimensional parameter-space in order to
make the MC generator predictions fit the data. It is desirable to achieve this
goal without spending too much time or computing resources iterating parameter
settings and comparing the same set of plots over and over again. We present
extensions and improvements to the MC tuning system, Professor, which addresses
the aforementioned problems by constructing a fast analytic model of a MC
generator which can then be easily fitted to data. Using this procedure it is
for the first time possible to get a robust estimate of the uncertainty of
generator tunings. Furthermore, we can use these uncertainty estimates to study
the effect of new (pseudo-) data on the quality of tunings and therefore decide
if a measurement is worthwhile in the prospect of generator tuning. The
potential of the Professor method outside the MC tuning area is presented as
well.Comment: To appear in the proceedings of the 13th International Workshop on
Advanced Computing and Analysis Techniques in Physics Research, ACAT2010,
Jaipur, India, February 22-27, 201
The F-box protein SKP2 mediates androgen control of p27 stability in LNCaP human prostate cancer cells
BACKGROUND: The cyclin-dependent kinase inhibitor p27 is a putative tumor suppressor that is downregulated in the majority of human prostate cancers. The mechanism of p27 down-regulation in prostate cancers in unknown, but presumably involves increased proteolysis mediated by the SCF(SKP2) ubiquitin ligase complex. Here we used the human prostate cancer cell line LNCaP, which undergoes G1 cell cycle arrest in response to androgen, to examine the role of the SKP2 F-box protein in p27 regulation in prostate cancer. RESULTS: We show that androgen-induced G1 cell cycle arrest of LNCaP cells coincides with inhibition of cyclin-dependent kinase 2 activity and p27 accumulation caused by reduced p27 ubiquitylation activity. At the same time, androgen decreased expression of SKP2, but did not affect other components of SCF(SKP2). Adenovirus-mediated overexpression of SKP2 led to ectopic down-regulation of p27 in asynchronous cells. Furthermore, SKP2 overexpression was sufficient to overcome p27 accumulation in androgen arrested cells by stimulating cellular p27 ubiquitylation activity. This resulted in transient activation of CDK2 activity, but was insufficient to override the androgen-induced G1 block. CONCLUSIONS: Our studies suggest that SKP2 is a major determinant of p27 levels in human prostate cancer cells. Based on our in vitro studies, we suggest that overexpression of SKP2 may be one of the mechanisms that allow prostate cancer cells to escape growth control mediated by p27. Consequently, the SKP2 pathway may be a suitable target for novel prostate cancer therapies
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