| 1. |
- Alimena, Juliette, et al.
(författare)
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Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider
- 2020
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Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 47:9
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Tidskriftsartikel (refereegranskat)abstract
- Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments-as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER-to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the high-luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity 'dark showers', highlighting opportunities for expanding the LHC reach for these signals.
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| 2. |
- Abdullahi, Asli M., et al.
(författare)
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The present and future status of heavy neutral leptons
- 2023
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Ingår i: Journal of Physics G. - : Institute of Physics Publishing (IOPP). - 0954-3899 .- 1361-6471. ; 50:2
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Tidskriftsartikel (refereegranskat)abstract
- The existence of nonzero neutrino masses points to the likely existence of multiple Standard Model neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as heavy neutral leptons (HNLs). In this white paper, we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding of key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios.
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| 3. |
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| 4. |
- Buckley, Andy, et al.
(författare)
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The HepMC3 event record library for Monte Carlo event generators
- 2021
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 260
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Tidskriftsartikel (refereegranskat)abstract
- In high-energy physics, Monte Carlo event generators (MCEGs) are used to simulate the interactions of high energy particles. MCEG event records store the information on the simulated particles and their relationships, and thus reflect the simulated evolution of physics phenomena in each collision event. We present the HepMC3 library, a next-generation framework for MCEG event record encoding and manipulation, which builds on the functionality of its widely-used predecessors to enable more sophisticated algorithms for event-record analysis. As compared to previous versions, the event record structure has been simplified, while adding the possibility to encode arbitrary information. The I/O functionality has been extended to support common input and output formats of various HEP MCEGs, including formats used in Fortran MCEGs, the formats established by the HepMC2 library, and binary formats such as ROOT; custom input or output handlers may also be used. HepMC3 is already supported by popular modern MCEGs and can replace the older HepMC versions in many others.
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| 5. |
- Cooke, Naomi, et al.
(författare)
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Non-relativistic quantum chromodynamics in parton showers
- 2024
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Ingår i: European Physical Journal C. - 1434-6044. ; 84:4
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of quarkonia isolation in jets at the Large Hadron Collider (LHC) have been shown to disagree with fixed-order non-relativistic quantum chromodynamics (NRQCD) calculations, even at higher orders. Calculations using the fragmenting jet function formalism are able to better describe data but cannot provide full event-level predictions. In this work we provide an alternative model via NRQCD production of quarkonia in a timelike parton shower. We include this model in the Pythia 8 event generator and validate our parton-shower implementation against analytic forms of the relevant fragmentation functions. Finally, we make inclusive predictions of quarkonia production for the decay of the standard-model Higgs boson.
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| 6. |
- Ilten, Philip, et al.
(författare)
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Forming molecular states with hadronic rescattering
- 2022
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 58:1
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Tidskriftsartikel (refereegranskat)abstract
- A method for modelling the prompt production of molecular states using the hadronic rescattering framework of the general-purpose Pythia event generator is introduced. Production cross sections of possible exotic hadronic molecules via hadronic rescattering at the LHC are calculated for the χc1(3872) resonance, a possible tetraquark state, as well as three possible pentaquark states, Pc+(4312), Pc+(4440), and Pc+(4457). For the Pc+ states, the expected cross section from Λ b decays is compared to the hadronic-rescattering production. The χc1(3872) cross section is compared to the fiducial χc1(3872) cross-section measurement by LHCb and found to contribute at a level of O(1 %). Finally, the expected yields of Pc+ production from hadronic rescattering during Run 3 of LHCb are estimated. The prompt background is found to be significantly larger than the prompt Pc+ signal from hadronic rescattering.
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| 7. |
- 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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| 8. |
- Valassi, Andrea, et al.
(författare)
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Challenges in Monte Carlo Event Generator Software for High-Luminosity LHC
- 2021
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Ingår i: Computing and Software for Big Science. - : Springer Science and Business Media LLC. - 2510-2044 .- 2510-2036. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- We review the main software and computing challenges for the Monte Carlo physics event generators used by the LHC experiments, in view of the High-Luminosity LHC (HL-LHC) physics programme. This paper has been prepared by the HEP Software Foundation (HSF) Physics Event Generator Working Group as an input to the LHCC review of HL-LHC computing, which has started in May 2020.
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