100 research outputs found
Measuring Sparticles with the Matrix Element
We apply the Matrix Element Method (MEM) to mass determination of squark pair
production with direct decay to quarks and LSP at the LHC, showing that
simultaneous mass determination of squarks and LSP is possible. We furthermore
propose methods for inclusion of QCD radiation effects in the MEM.Comment: 4 pages, 2 figures. To appear in the proceedings of SUSY09, the 17th
International Conference on Supersymmetry and the Unification of Fundamental
Interactions. Figures replaced (corrected y axis labels
Automatic spin-entangled decays of heavy resonances in Monte Carlo simulations
We present a general method that allows one to decay narrow resonances in Les
Houches Monte Carlo events in an efficient and accurate way. The procedure
preserves both spin correlation and finite width effects to a very good
accuracy, and is therefore particularly suited for the decay of resonances in
production events generated at next-to-leading-order accuracy. The method is
implemented as a generic tool in the MadGraph framework, giving access to a
very large set of possible applications. We illustrate the validity of the
method and the code by applying it to the case of single top and top quark pair
production, and show its capabilities on the case of top quark pair production
in association with a Higgs boson.Comment: 17 pages, 6 figures, published versio
Reconstructing the invisible with matrix elements
We propose a fully flexible method to perform an hypothesis test between
signal and background based on the Matrix Element Method in the presence of
multiple invisible particles. The proposed method performs a mapping of the
measured final state onto its minimal hypersurface of degrees of freedom for a
given process and then maximises the matrix element on this hypersurface
separately for signal and background. To show how performant the method is in
separating signal from background, we apply it to the prominent partly
invisible decay of a Higgs boson into a muon-antimuon pair and two
muon-neutrinos via two W bosons.Comment: 4 page
Direct Detection of Dark Matter with MadDM v.2.0
We present MadDM v.2.0, a numerical tool for dark matter physics in a generic
model. This version is the next step towards the development of a fully
automated framework for dark matter searches at the interface of collider
physics, astro-physics and cosmology. It extends the capabilities of v.1.0 to
perform calculations relevant to the direct detection of dark matter. These
include calculations of spin-independent/spin-dependent nucleon scattering
cross sections and nuclear recoil rates (as a function of both energy and
angle), as well as a simplified functionality to compare the model points with
existing constraints. The functionality of MadDM v.2.0 incorporates a large
selection of dark matter detector materials and sizes, and simulates detector
effects on the nuclear recoil signals. We validate the code in a wide range of
dark matter models by comparing results from MadDM v.2.0 to the existing tools
and literature.Comment: 38 pages, 8 figures, 5 tables; v2. Matches the version accepted for
publication in Physics of the Dark Universe. We have improved table IV by
validating the other sps points of the MSS
Unravelling via the matrix element method
Associated production of the Higgs boson with a top-antitop pair is a key
channel to gather further information on the nature of the newly discovered
boson at the LHC. Experimentally, however, its observation is very challenging
due to the combination of small rates, difficult multi-jet final states and
overwhelming backgrounds. In the Standard Model the largest number of events is
expected when h->bb, giving rise to a WWbbbb signature, deluged in tt+jets. A
promising strategy to improve the sensitivity is to maximally exploit the
theoretical information on the signal and background processes by means of the
matrix element method. We show how, despite the complexity of the final state,
the method can be efficiently applied to discriminate the signal against
combinatorial and tt+jets backgrounds. Remarkably, we find that a moderate
integrated luminosity in the next LHC run will be enough to make the signature
involving both W's decaying leptonically as sensitive as the single-lepton one.Comment: 4 pages, 2 figure
Searching for New Long Lived Particles in Heavy Ion Collisions at the LHC
We show that heavy ion collisions at the LHC provide a promising environment
to search for new long lived particles in well-motivated New Physics scenarios.
One advantage lies in the possibility to operate the main detectors with looser
triggers, which can increase the number of observable events by orders of
magnitude if the long lived particles are produced with low transverse
momentum. In addition, the absence of pileup in heavy ion collisions can avoid
systematic nuisances that will be present in future proton runs, such as the
problem of vertex mis-identification. Finally, there are new production
mechanisms that are absent or inefficient in proton collisions. We show that
the looser triggers alone can make searches in heavy ion data competitive with
proton data for the specific example of heavy neutrinos in the Neutrino Minimal
Standard Model, produced in the decay of B mesons. Our results suggest that
collisions of ions lighter than lead, which are currently under discussion in
the heavy ion community, are well-motivated from the viewpoint of searches for
New Physics.Comment: Version accepted by Physical Review Letters for publication as a
Letter. 6 pages, 3 figure
MadDM: New Dark Matter Tool in the LHC era
We present the updated version of MadDM, a new dark matter tool based on
MadGraph5_aMC@NLO framework. New version includes direct detection capability
in addition to relic abundance computation. In this article, we provide short
description of the implementation of relevant effective operators and
validations against existing results in literature.Comment: 4 pages. Submitted to the proceedings of PPC 201
Event generation for beam dump experiments
A wealth of new physics models which are motivated by questions such as the
nature of dark matter, the origin of the neutrino masses and the baryon
asymmetry in the universe, predict the existence of hidden sectors featuring
new particles. Among the possibilities are heavy neutral leptons, vectors and
scalars, that feebly interact with the Standard Model (SM) sector and are
typically light and long lived. Such new states could be produced in
high-intensity facilities, the so-called beam dump experiments, either directly
in the hard interaction or as a decay product of heavier mesons. They could
then decay back to the SM or to hidden sector particles, giving rise to
peculiar decay or interaction signatures in a far-placed detector. Simulating
such kind of events presents a challenge, as not only short-distance new
physics (hard production, hadron decays, and interaction with the detector) and
usual SM phenomena need to be described but also the travel has to be accounted
for as determined by the geometry of the detector. In this work, we describe a
new plugin to the {\sc MadGraph5\_aMC@NLO} platform, which allows the complete
simulation of new physics processes relevant for beam dump experiments,
including the various mechanisms for the production of hidden particles, namely
their decays or scattering off SM particles, as well as their far detection,
keeping into account spatial correlations and the geometry of the experiment.Comment: LaTeX, 42 pages, 14 figure
Design and engineering of a simplified workflow execution for the MG5aMC event generator on GPUs and vector CPUs
Physics event generators are essential components of the data analysis
software chain of high energy physics experiments, and important consumers of
their CPU resources. Improving the software performance of these packages on
modern hardware architectures, such as those deployed at HPC centers, is
essential in view of the upcoming HL-LHC physics programme. In this paper, we
describe an ongoing activity to reengineer the Madgraph5_aMC@NLO physics event
generator, primarily to port it and allow its efficient execution on GPUs, but
also to modernize it and optimize its performance on vector CPUs. We describe
the motivation, engineering process and software architecture design of our
developments, as well as the current challenges and future directions for this
project. This paper is based on our submission to vCHEP2021 in March
2021,complemented with a few preliminary results that we presented during the
conference. Further details and updated results will be given in later
publications.Comment: 17 pages, 6 figures, submitted to vCHEP2021 proceedings in EPJ Web of
Conferences; minor changes to address comments from the EPJWOC reviewe
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