| 1. |
- Buckley, Andy, et al.
(författare)
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General-purpose event generators for LHC physics
- 2011
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573. ; 504:5, s. 145-233
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Forskningsöversikt (refereegranskat)abstract
- We review the physics basis, main features and use of general-purpose Monte Carlo event generators for the simulation of proton-proton collisions at the Large Hadron Collider. Topics included are: the generation of hard scattering matrix elements for processes of interest, at both leading and next-to-leading QCD perturbative order; their matching to approximate treatments of higher orders based on the showering approximation; the parton and dipole shower formulations; parton distribution functions for event generators; non-perturbative aspects such as soft QCD collisions, the underlying event and diffractive processes; the string and cluster models for hadron formation; the treatment of hadron and tau decays; the inclusion of QED radiation and beyond Standard Model processes. We describe the principal features of the ARIADNE, Herwig++, PYTHIA 8 and SHERPA generators, together with the Rivet and Professor validation and tuning tools, and discuss the physics philosophy behind the proper use of these generators and tools. This review is aimed at phenomenologists wishing to understand better how parton-level predictions are translated into hadron-level events as well as experimentalists seeking a deeper insight into the tools available for signal and background simulation at the LHC. (C) 2011 Elsevier B.V. All rights reserved.
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| 2. |
- Abada, A., et al.
(författare)
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Future Circular Collider : Vol. 1 Physics opportunities
- 2018
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Ingår i: Future Circular Collider. - : Springer Science and Business Media LLC.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We review the physics opportunities of the Future Circular Collider, covering its e+e-, pp, ep and heavy ion programmes. We describe the measurement capabilities of each FCC component, addressing the study of electroweak, Higgs and strong interactions, the top quark and flavour, as well as phenomena beyond the Standard Model. We highlight the synergy and complementarity of the different colliders, which will contribute to a uniquely coherent and ambitious research programme, providing an unmatchable combination of precision and sensitivity to new physics.
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| 3. |
- Abada, A., et al.
(författare)
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Future Circular Collider : Vol. 2 The Lepton Collider (FCC-ee)
- 2019
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Ingår i: Future Circular Collider. - : Springer Science and Business Media LLC.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In response to the 2013 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) study was launched, as an international collaboration hosted by CERN. This study covers a highest-luminosity high-energy lepton collider (FCC-ee) and an energy-frontier hadron collider (FCC-hh), which could, successively, be installed in the same 100 km tunnel. The scientific capabilities of the integrated FCC programme would serve the worldwide community throughout the 21st century. The FCC study also investigates an LHC energy upgrade, using FCC-hh technology. This document constitutes the second volume of the FCC Conceptual Design Report, devoted to the electron-positron collider FCC-ee. After summarizing the physics discovery opportunities, it presents the accelerator design, performance reach, a staged operation scenario, the underlying technologies, civil engineering, technical infrastructure, and an implementation plan. FCC-ee can be built with today’s technology. Most of the FCC-ee infrastructure could be reused for FCC-hh. Combining concepts from past and present lepton colliders and adding a few novel elements, the FCC-ee design promises outstandingly high luminosity. This will make the FCC-ee a unique precision instrument to study the heaviest known particles (Z, W and H bosons and the top quark), offering great direct and indirect sensitivity to new physics.
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| 4. |
- Abada, A., et al.
(författare)
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Future Circular Collider : Vol. 3 The Hadron Collider (FCC-hh)
- 2019
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Ingår i: Future Circular Collider. - : Springer Science and Business Media LLC.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Particle physics has arrived at an important moment of its history. The discovery of the Higgs boson, with a mass of 125 GeV, completes the matrix of particles and interactions that has constituted the “Standard Model” for several decades. This model is a consistent and predictive theory, which has so far proven successful at describing all phenomena accessible to collider experiments. However, several experimental facts do require the extension of the Standard Model and explanations are needed for observations such as the abundance of matter over antimatter, the striking evidence for dark matter and the non-zero neutrino masses. Theoretical issues such as the hierarchy problem, and, more in general, the dynamical origin of the Higgs mechanism, do likewise point to the existence of physics beyond the Standard Model. This report contains the description of a novel research infrastructure based on a highest-energy hadron collider with a centre-of-mass collision energy of 100 TeV and an integrated luminosity of at least a factor of 5 larger than the HL-LHC. It will extend the current energy frontier by almost an order of magnitude. The mass reach for direct discovery will reach several tens of TeV, and allow, for example, to produce new particles whose existence could be indirectly exposed by precision measurements during the earlier preceding e+e– collider phase. This collider will also precisely measure the Higgs self-coupling and thoroughly explore the dynamics of electroweak symmetry breaking at the TeV scale, to elucidate the nature of the electroweak phase transition. WIMPs as thermal dark matter candidates will be discovered, or ruled out. As a single project, this particle collider infrastructure will serve the world-wide physics community for about 25 years and, in combination with a lepton collider (see FCC conceptual design report volume 2), will provide a research tool until the end of the 21st century. Collision energies beyond 100 TeV can be considered when using high-temperature superconductors. The European Strategy for Particle Physics (ESPP) update 2013 stated “To stay at the forefront of particle physics, Europe needs to be in a position to propose an ambitious post-LHC accelerator project at CERN by the time of the next Strategy update”. The FCC study has implemented the ESPP recommendation by developing a long-term vision for an “accelerator project in a global context”. This document describes the detailed design and preparation of a construction project for a post-LHC circular energy frontier collider “in collaboration with national institutes, laboratories and universities worldwide”, and enhanced by a strong participation of industrial partners. Now, a coordinated preparation effort can be based on a core of an ever-growing consortium of already more than 135 institutes worldwide. The technology for constructing a high-energy circular hadron collider can be brought to the technology readiness level required for constructing within the coming ten years through a focused R&D; programme. The FCC-hh concept comprises in the baseline scenario a power-saving, low-temperature superconducting magnet system based on an evolution of the Nb3Sn technology pioneered at the HL-LHC, an energy-efficient cryogenic refrigeration infrastructure based on a neon-helium (Nelium) light gas mixture, a high-reliability and low loss cryogen distribution infrastructure based on Invar, high-power distributed beam transfer using superconducting elements and local magnet energy recovery and re-use technologies that are already gradually introduced at other CERN accelerators. On a longer timescale, high-temperature superconductors can be developed together with industrial partners to achieve an even more energy efficient particle collider or to reach even higher collision energies.The re-use of the LHC and its injector chain, which also serve for a concurrently running physics programme, is an essential lever to come to an overall sustainable research infrastructure at the energy frontier. Strategic R&D; for FCC-hh aims at minimising construction cost and energy consumption, while maximising the socio-economic impact. It will mitigate technology-related risks and ensure that industry can benefit from an acceptable utility. Concerning the implementation, a preparatory phase of about eight years is both necessary and adequate to establish the project governance and organisation structures, to build the international machine and experiment consortia, to develop a territorial implantation plan in agreement with the host-states’ requirements, to optimise the disposal of land and underground volumes, and to prepare the civil engineering project. Such a large-scale, international fundamental research infrastructure, tightly involving industrial partners and providing training at all education levels, will be a strong motor of economic and societal development in all participating nations. The FCC study has implemented a set of actions towards a coherent vision for the world-wide high-energy and particle physics community, providing a collaborative framework for topically complementary and geographically well-balanced contributions. This conceptual design report lays the foundation for a subsequent infrastructure preparatory and technical design phase.
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| 5. |
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| 6. |
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| 7. |
- Bothmann, Enrico, et al.
(författare)
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A standard convention for particle-level Monte Carlo event-variation weights
- 2023
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Ingår i: SciPost Physics Core. - 2666-9366. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Streams of event weights in particle-level Monte Carlo event generators are a convenient and immensely CPU-efficient approach to express systematic uncertainties in phenomenology calculations, providing systematic variations on the nominal prediction within a single event sample. But the lack of a common standard for labelling these variation streams across different tools has proven to be a major limitation for event-processing tools and analysers alike. Here we propose a well-defined, extensible community standard for the naming, ordering, and interpretation of weight streams that will serve as the basis for semantically correct parsing and combination of such variations in both theoretical and experimental studies.
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| 8. |
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| 9. |
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| 10. |
- Christiansen, Jesper Roy, et al.
(författare)
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String formation beyond leading colour
- 2015
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :8
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Tidskriftsartikel (refereegranskat)abstract
- We present a new model for the hadronisation of multi-parton systems, in which colour correlations beyond leading N-C are allowed to influence the formation of confining potentials (strings). The multiplet structure of SU(3) is combined with a minimisation of the string potential energy, to decide between which partons strings should form, allowing also for "baryonic" configurations (e.g., two colours can combine coherently to form an anticolour). In e(+)e (-) collisions, modifications to the leading-colour picture are small, suppressed by both colour and kinematics factors. But in pp collisions, multi-parton interactions increase the number of possible subleading connections, counteracting their naive 1/N-C(2) suppression. Moreover, those that reduce the overall string lengths are kine-matically favoured. The model, which we have implemented in the PYTHIA 8 generator, is capable of reaching agreement not only with the important < p perpendicular to >(n(charged)) distribution but also with measured rates (and ratios) of kaons and hyperons, in both ee and pp collisions. Nonetheless, the shape of their p perpendicular to spectra remains challenging to explain.
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| 11. |
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| 12. |
- Fairbairn, M., et al.
(författare)
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Stable massive particles at colliders
- 2007
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573. ; 438:1, s. 1-63
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Forskningsöversikt (refereegranskat)abstract
- We review the theoretical motivations and experimental status of searches for stable massive particles (SMPs) which could be sufficiently long-lived as to be directly detected at collider experiments. The discovery of such particles would address a number of important questions in modern physics including the origin and composition of dark matter in the universe and the unification of the fundamental forces. This review describes the techniques used in SNIP-searches at collider experiments and the limits so far obtained on the production of SMPs which possess various colour, electric and magnetic charge quantum numbers. We also describe theoretical scenarios which predict SMPs along with the phenomenology needed to model their production at colliders and interactions with matter. In addition, the interplay between collider searches and open questions in cosmology such as dark matter composition is addressed. (c) 2006 Elsevier B.V. All rights reserved.
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| 13. |
- Gras, Philippe, et al.
(författare)
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Systematics of quark/gluon tagging
- 2017
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2017:7
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Tidskriftsartikel (refereegranskat)abstract
- By measuring the substructure of a jet, one can assign it a “quark” or “gluon” tag. In the eikonal (double-logarithmic) limit, quark/gluon discrimination is determined solely by the color factor of the initiating parton (CF versus CA). In this paper, we confront the challenges faced when going beyond this leading-order understanding, using both parton-shower generators and first-principles calculations to assess the impact of higher-order perturbative and nonperturbative physics. Working in the idealized context of electron-positron collisions, where one can define a proxy for quark and gluon jets based on the Lorentz structure of the production vertex, we find a fascinating interplay between perturbative shower effects and nonperturbative hadronization effects. Turning to proton-proton collisions, we highlight a core set of measurements that would constrain current uncertainties in quark/gluon tagging and improve the overall modeling of jets at the Large Hadron Collider.
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| 14. |
- Sjöstrand, Torbjörn, et al.
(författare)
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A Brief Introduction to PYTHIA 8.1
- 2008
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 178:11, s. 852-867
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe PYTHIA program is a standard tool for the generation of high-energy collisions, comprising a coherent set of physics models for the evolution from a few-body hard process to a complex multihadronic final state. It contains a library of hard processes and models for initial-and final-state parton showers, multiple parton-parton interactions, beam remnants, string fragmentation and particle decays. It also has a set of utilities and interfaces to external programs. While previous versions were written in Fortran, PYTHIA 8 represents a complete rewrite in C++. The current release is the first main one after this transition, and does not yet in every respect replace the old code. It does contain some new physics aspects, on the other hand, that should make it an attractive option especially for LHC physics studies.
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| 15. |
- Sjöstrand, Torbjörn, et al.
(författare)
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An introduction to PYTHIA 8.2
- 2015
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 191, s. 159-177
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Tidskriftsartikel (refereegranskat)abstract
- The PYTHIA program is a standard tool for the generation of events in high-energy collisions, comprising a coherent set of physics models for the evolution from a few-body hard process to a complex multiparticle final state. It contains a library of hard processes, models for initial- and final-state parton showers, matching and merging methods between hard processes and parton showers, multiparton interactions, beam remnants, string fragmentation and particle decays. It also has a set of utilities and several interfaces to external programs. PYTHIA 8.2 is the second main release after the complete rewrite from Fortran to C++, and now has reached such a maturity that it offers a complete replacement for most applications, notably for LHC physics studies. The many new features should allow an improved description of data. New version program summary Program title: PYTHIA 8.2 Catalogue identifier: ACTU_v4_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ACTU_v4_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public Licence, version 2 No. of lines in distributed program, including test data, etc.: 478360 No. of bytes in distributed program, including test data, etc.: 14131810 Distribution format: tar.gz Programming language: C++. Computer: Commodity PCs, Macs. Operating system: Linux, OS X; should also work on other systems. RAM: 10 megabytes Classification: 11.2. Does the new version supersede the previous version?: Yes Catalogue identifier of previous version: ACTU_v3_0 Journal reference of previous version: Comput Phys. Comm. 178 (2008) 852 Nature of problem: High-energy collisions between elementary particles normally give rise to complex final states, with large multiplicities of hadrons, leptons, photons and neutrinos. The relation between these final states and the underlying physics description is not a simple one, for two main reasons. Firstly, we do not even in principle have a complete understanding of the physics. Secondly, any analytical approach is made intractable by the large multiplicities. Solution method: Complete events are generated by Monte Carlo methods. The complexity is mastered by a subdivision of the full problem into a set of simpler separate tasks. All main aspects of the events are simulated, such as hard-process selection, initial- and final-state radiation, beam remnants, fragmentation, decays, and so on. Therefore events should be directly comparable with experimentally observable ones. The programs can be used to extract physics from comparisons with existing data, or to. study physics at future experiments. Reasons for new version: Improved and expanded physics models. Summary of revisions: Hundreds of new features and bug fixes, allowing improved modelling. Restrictions: Depends on the problem studied. Running time: 10-1000 events per second, depending on process studied. (C) 2015 Elsevier B.V. All rights reserved.
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| 16. |
- Sjöstrand, Torbjörn, et al.
(författare)
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Baryon number violation and string topologies
- 2003
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Ingår i: Nuclear Physics, Section B. - 0550-3213. ; 659:1-2, s. 243-298
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Tidskriftsartikel (refereegranskat)abstract
- In supersymmetric scenarios with broken R-parity, baryon number violating sparticle decays become possible. In order to search for such decays, a good understanding of expected event properties is essential. We here develop a complete framework that allows detailed studies. Special attention is given to the hadronization phase, wherein the baryon number violating vertex is associated with the appearance of a junction in the colour confinement field. This allows us to tell where to look for the extra (anti)baryon directly associated with the baryon number violating decay. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 17. |
- Sjöstrand, T., et al.
(författare)
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Multiple interactions and beam remnants
- 2004
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Ingår i: Physics at TeV colliders. Proceedings, Workshop, Les Houches, France, May 26-June 3, 2003.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 18. |
- Sjöstrand, Torbjörn, et al.
(författare)
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Multiple interactions and the structure of beam remnants
- 2004
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; :3
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 19. |
- Sjöstrand, Torbjörn, et al.
(författare)
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PYTHIA 6.4 physics and manual
- 2006
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; 5
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 20. |
- Sjöstrand, Torbjörn, et al.
(författare)
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Transverse-momentum-ordered showers and interleaved multiple interactions
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 39:2, s. 129-154
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a sophisticated framework for high-energy hadronic collisions, wherein different QCD physics processes are interleaved in a common sequence of falling transverse-momentum values. Thereby phase-space competition is introduced between multiple parton-parton interactions and initial-state radiation. As a first step we develop new transverse-momentum-ordered showers for initial- and final-state radiation, which should be of use also beyond the scope of the current article. These showers are then applied in the context of multiple interactions, and a few tests of the new model are presented. The article concludes with an outlook on further aspects, such as the possibility of a shower branching giving partons participating in two different interactions.
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| 21. |
- Skands, Peter
(författare)
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Phenomenological Studies on Supersymmetry and the Strong Force
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, we first consider the phenomenology of R-parity violating supersymmetric extensions of the Standard Model. Specifically, a large number of Lepton and Baryon Number violating decays of sparticles to particles are implemented in the Pythia event generator. The augmented generator has then been used to study event properties of these models, mainly at the LHC. During these studies, the development of the so-called SuSy Les Houches Accord opened for an easier interfacing between SuSy calculational tools. A first `proof-of-concept' application of the Accord was to input SuSy spectra and decay tables calculated by the SPheno program into Pythia, for the purpose of determining whether experiments at the LHC will be sensitive to a connection between neutrino mixing and SuSy with bilinear Lepton Number violation. For the case of Baryon Number violation, an extension of the Lund String Model to colour topologies involving explicit Baryon Numbers is developed, called `junction fragmentation', which enables us to trace the migration of the generated Baryon number in some detail. This model is then itself extended and applied to improve the description of the physics of beam remnants in hadron--hadron collisions, in the context of a new framework for minimum-bias and underlying events. Based on the idea of multiple perturbative parton--parton interactions in hadron collisions, a sophisticated treatment of correlations in impact parameter, flavour, momentum, and colour is introduced. The last step so far in the evolution of this model has been the development of pT-ordered initial- and final-state radiation algorithms, which among other things have enabled us to `interleave' initial-state radiation and multiple interactions into one common sequence of decreasing pT values. Nonetheless, there is still a long way to go before a clear and unique picture of hadron collisions may emerge.
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| 22. |
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| 23. |
- Skands, Peter
(författare)
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Searching for L-violating supersymmetry at the LHC
- 2002
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 23:1, s. 173-184
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Tidskriftsartikel (refereegranskat)abstract
- The possibility to simulate lepton number violating supersymmetric models has been introduced into the recently updated Pythia event generator, now containing 1278 decay channels of SUSY particles into SM particles via lepton number violating interactions. This generator has been used in combination with the AtlFast detector simulation to study the impact of lepton number violation (4) on event topologies in the ATLAS detector, and trigger menus designed for L-SUSY are proposed based on very general considerations. In addition. a rather preliminary analysis is presented on the possibility for ATLAS to observe a signal above the background in several mSUGRA scenarios, using a combination of primitive cuts and neural networks to optimize the discriminating power between signal and background events over regions of parameter space rather than at individual points. It is found that a 5sigma discovery is possible roughly for m(1/2) < 1 TeV and m(0) < 2TeV with an integrated luminosity of 30fb(-1), corresponding to one year of data taking with the LHC running at "mid-luminosity", L = 3 x 10(33) cm(-2)s(-1).
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| 24. |
- Skands, Peter, et al.
(författare)
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SUSY Les Houches accord: interfacing SUSY spectrum calculators, decay packages, and event generators
- 2004
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :7
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Tidskriftsartikel (refereegranskat)abstract
- An accord specifying a unique set of conventions for supersymmetric extensions of the Standard Model together with generic file structures for 1) supersymmetric model specifications and input parameters, 2) electroweak scale supersymmetric mass and coupling spectra, and 3) decay tables is presented, to provide a universal interface between spectrum calculation programs, decay packages, and high energy physics event generators.
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