70 research outputs found
The p¯p → tbH± process at the Tevatron in HERWIG and PYTHIA simulations
No full textCharged Higgs boson production in association with a top quark could be the first indication of the existence of Higgs particles. The Tevatron Run-II started data-taking in April 2001 at GeV and could probe the existence of a charged Higgs boson beyond the current mass limit. We study the production process with Monte Carlo simulations in HERWIG and PYTHIA, comparing expected cross sections and basic selection variables
Dark matter-motivated searches for exotic fourth-generation mirror quarks in Tevatron and early LHC data
No full textWe determine the prospects for finding dark matter at the Tevatron and LHC through the production of exotic fourth-generation mirror quarks T ′ that decay through T′→tX, where X is dark matter. The resulting signal of tt̄+ET has not previously been considered in searches for fourth-generation quarks, but there are both general and specific dark matter motivations for this signal, and with slight modifications, this analysis applies to any scenario where invisible particles are produced in association with top quarks. Current direct and indirect bounds on such exotic quarks restrict their masses to be between 300 and 600 GeV, and the dark matter's mass may be anywhere below mT′. We simulate the signal and main backgrounds with MadGraph/MadEvent-Pythia-PGS4. For the Tevatron, we find that an integrated luminosity of 20fb-1 will allow 3σ discovery up to mT′=400GeV and 95% exclusion up to mT′=455GeV. For the 10 TeV LHC with 300pb-1, the discovery and exclusion sensitivities rise to 490 GeV and 600 GeV. These scenarios are therefore among the most promising for dark matter at colliders. Perhaps most interestingly, we find that dark matter models that can explain results from the DAMA, CDMS, and CoGeNT collaborations can be tested with high statistical significance using data already collected at the Tevatron and have extraordinarily promising implications for early runs of the LHC. © 2010 The American Physical Society
QCD radiation in the production of heavy colored particles at the LHC
No full textWe present a study of the effects of QCD radiation in the production of heavy colored states, employing inclusive multi-jet samples obtained by matching matrix elements and parton showers. We discuss several examples showing that matched samples are in general not only more accurate than a parton shower alone, but also sometimes indispensable to make reliable predictions of beyond the Standard Model signals
Innovations from the Baltic Sea regionNils Alwall, Lembit Norviit, Adolfs Martins Steins and the artificial kidney
No full textPublisher Copyright: © 2023, The Author(s).In connection with the construction of one of the first practical dialysis machines, medical historians emphasize the work of the Swedish physician Nils Alwall. Together with his colleagues, he developed a device in the 1940s that could implement the combination of dialysis and ultrafiltration with membranes (cellophane tubes). Little known is the involvement of the physicians Lembit Norviit from Estonia and Adolfs Martins Steins from Latvia, both coauthors of the influential research article Clinical extracorporeal dialysis of blood with artificial kidney that was published in The Lancet in 1948 and the transfer of knowledge between Estonian, Latvian and Swedish researchers.Peer reviewe
MadGraph 5: going beyond
No full textMadGraph 5 is the new version of the MadGraph matrix element generator,
written in the Python programming language. It implements a number of new,
efficient algorithms that provide improved performance and functionality in all aspects of
the program. It features a new user interface, several new output formats including C++
process libraries for Pythia 8, and full compatibility with FeynRules for new physics
models implementation, allowing for event generation for any model that can be written
in the form of a Lagrangian. MadGraph 5 builds on the same philosophy as the previous
versions, and its design allows it to be used as a collaborative platform where theoretical,
phenomenological and simulation projects can be developed and then distributed to the
high-energy community. We describe the ideas and the most important developments of
the code and illustrate its capabilities through a few simple phenomenological examples
Matched predictions for Higgs production via heavy-quark loops in the standard model and beyond
No full textThe main Higgs production channel at hadron colliders is gluon fusion via heavy-quark loops. We present the results of a fully exclusive simulation of gluon fusion Higgs production based on the matrix elements for h+0, 1, 2 partons including full heavy-quark loop dependence, matched to a parton shower. We consider a Higgs with standard model couplings as well as models where the Higgs has enhanced couplings to bottom quarks (b-philic). We study the most relevant kinematic distributions, such as jet and Higgs pT spectra and find that matched samples provide an accurate description of the final state. For the SM Higgs, we confirm the excellent accuracy of the large heavy-quark-mass approximation also in differential distributions over all phase space, with significant effects arising only at large pT. For a b-philic Higgs however, the loops have a dramatic impact on the kinematics of the Higgs as well as of the jets and need to be accounted for exactly to achieve reliable event simulations
Quark Distributions and Charged Higgs Boson Production : Studies of Proton Structure and New Physics
No full textThe Standard Model describes all elementary particles known today, but at larger energies it will have to be complemented with new particles and interactions. To be able to distinguish new physics at proton colliders such as LHC at CERN, it is essential to have an appropriate description of the colliding protons and their interactions. The study of the proton is important also in itself, to get a better understanding of the non-perturbative aspects of the strong interaction. In paper I-IV of this thesis, a model for the non-perturbative dynamics of quarks and gluons is developed, based on quantum fluctuations in hadrons. The parton distributions of the proton are given by momentum fluctuations, with sea quark distributions generated by fluctuations into baryon-meson pairs. This model can reproduce proton structure function data, as well as measured asymmetries between up and down valence quark distributions and between the anti-up and anti-down sea. It provides an intrinsic charm quark component as indicated by data. It also predicts an asymmetry in the strange sea of the proton, which can explain the NuTeV anomaly first attributed to new physics beyond the Standard Model. Charged Higgs bosons are predicted by several theories for new physics, including Supersymmetry. At proton colliders, the predicted dominant production mechanism is in association with top and bottom quarks. In paper V-VII, different contributions to this production are studied, and an algorithm is developed for combining the two dominant processes gb -> tH+/- and gg -> tbH+/-. The algorithm gives a smooth transition from small to large transverse momenta of the b-quark, which is important when the b-quark is observed. It also gives arguments for the choice of factorisation scale in the process
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