484 research outputs found
Strange particle production in final states in collisions at TeV with the ATLAS detector at the LHC
No full textThe LHC has opened up a new era in particle physics in as much it paved the way for the discovery of the Higgs boson, the missing piece in the so called standard model (SM) , pushing the lower limits for particles predicted in many beyond the standard model (BSM) scenarios to values well above the TeV scale, allowing precision measurements at unprecedented energies. This ambitious scientific program has been carried out with the construction of two big multipurpose detectors: ATLAS and CMS. The discovery of the Higgs boson is, no doubt, one of the most important milestones in the history of particle physics. Another field where one can reach unprecedented precision is in the study of the top quark. With the advent of unprecedented statistics for top quark pair production, one can think of directly measuring the Cabibbo-Kobayashi-Maskawa matrix elements where the top quark is involved, in particular . Ali et al. [Phys. Lett. B 693 (2010) 44-51] made the proposal to determine this matrix element by discerning the signal final state from the dominant background process . This could be done by looking at neutral strange particle production which turns out to be leading in -quark jets while non-leading in -quark jets as -quarks decay sequentially . This proposal makes use of MVA techniques, with the possible existence of jet secondary vertices and soft leptons as additional variables with discriminant power. Therefore this proposal is dependent on the good agreement between data and Monte Carlo generators used in the training phase. However the proposal we refer to is qualitatively right, but quantitatively is somewhat overoptimistic as it is based on generator level data. The aim of the present thesis is twofold: on the one hand, as a continuation of the thesis presented in 2015 by Dr. Javier Llorente, who measured - and light-jet shapes in events, we have investigated the improvements in the performance of the MVA discussed above when adding the jet shapes as a discriminant variable. This was presented at ICHEP 2014 in Valencia, [Nucl. Part. Phys. Proc. 273-275 (2016) 2761-2763]. This is the basis for Chapter 4 in this thesis. On the other hand, we made use of the ATLAS data at 7 TeV taken in 2011, to study neutral strange particle production in the dileptonic final states. This study has been published in Eur. Phys. J. C 79 (2019) 1017. It is found that neutral strange particle production embedded in jets, -tagged or not, is well described by current MC models like the following generators: POWHEG+PYTHIA6, POWHEG+PYTHIA8, MC@NLO+HERWIG, POWHEG+HERWIG7, aMC@NLO+HERWIG7 or SHERPA. This lends support to the idea put forward by ABL that one could attempt to determine with a TMVA. Furthermore, neutral strange particles produced outside jets, the dominant contribution, in underestimated by current MC generators by 30 %. Thus, these data have the potential to help tune models for MPI. This is summarised in Chapter 5. For the sake of completeness and without any pretension to originality, the first three chapters are devoted to present the most relevant aspects of the SM, Chapter 1, the ATLAS detector and the LHC, Chapter 2, and the objects (leptons, jets, missing energy) reconstruction, Chapter 3
Measurements of and production in dileptonic events in collisions at with the ATLAS detector.
No full textMeasurements of and production in final states have been performed. They are based on a data sample with integrated luminosity of 4.6 from proton--proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 with the ATLAS detector at the Large Hadron Collider. Neutral strange particles are separated into three classes, depending on whether they are contained in a jet, with or without a -tag, or not associated with a selected jet. The aim is to look for differences in their main kinematic distributions. A comparison of data with several Monte Carlo simulations using different hadronisation and fragmentation schemes, colour reconnection models and different tunes for the underlying event has been made. The production of neutral strange particles in dileptonic events is found to be well described by current Monte Carlo models for and production within jets, but not for those produced outside jets
Fragmentation studies with the ATLAS detector
No full textGluon splitting to b-quark pairs is a unique probe into the properties of gluon fragmentation, as identified b-tagged jets provide a proxy for the quark daughters of the initial gluon. If available, we present a measurement of key differential distributions related to g→b bbar using data collected with the ATLAS detector at √s=13 TeV. Track jets are used to probe angular scales below the standard R=0.4 jet radius. The observables are unfolded to particle level in order to facilitate direct comparison with predictions from simulations and provide an important constraint to hadronization models. If available, a measurement of the properties of jet fragmentation performed with pp data collected with the ATLAS detector at √s=13 TeV is presented. Charged particle tracks are used to measure charged particle multiplicity, the jet charge, the summed fragmentation function, the momentum transverse to the jet axis, and the radial profile of the jet. Each observable is unfolded to correct for acceptance and detector effects. Exclusive interpretations in terms of quarks and gluons are provided in order to directly compare with state-of-the-art calculations
Fatigue Life Response of P355NL1 Steel under Uniaxial Loading Using Kohout-Věchet Model
No full textAbstractThe fatigue life of materials and structural details can be characterized by distinct fatigue regimes. These regimes may range from quasi-static monotonic loading to very high cyclic fatigue. The Kohout-Věchet (KV) fatigue model describes the damage regimes since the limiting tensile strength to the permanent fatigue limit. In this paper, the fatigue S-N response of the P355NL1 steel, using smooth specimens under uniaxial stress states, is characterized based on the original suggestion by Kohout and Věchet. The experimental results related to the fatigue behavior of the P355NL1 steel were obtained through fatigue tests under stress-control conditions, covering distinct stress ratios. This study validates the importance and applicability of the global S-N models to describe the Wöhler S-N curve, from tensile strength to the fatigue limit, in the fatigue life evaluation of structural details
Joint evaluation of fracture results from distinct test conditions, implying loading, specimen size and geometry
No full textAbstractThe reliability of the statistical assessment of test results is strong influenced by the reduced data size emanating from the low number of specimens included in each of the groups, characterized by test type, specimen geometry and size implied in the material sample being tested. Due to the traditional economical and time limitations, the available experimental results owned by a research group lack of parameter diversity so that they must be complemented by foreign results reported elsewhere in order to verify a model, a methodology or reinforced probabilistic conclusions. Generally, difficulties arise in assessing the parameters involved in the phenomenon due to the diversity of samples and test conditions supported by few data results. In this paper, a methodology based on a generalized local model, denoted GLM, is proposed to overcome this limitation allowing a joint evaluation diversified tests as those resulting from different loading conditions and specimen shape and size. It implies the primary failure cumulative distribution function, PFCDF, as the failure characteristic of the material to be derived from experimental results obtained from distinct test programs. In this work, the local methodology is applied for probabilistic assessment of cleavage fracture toughness data of steel A533B lent from an external experimental program carried out by Rathbun et al. (2006), aiming at analyzing the constraint influence on the cleavage fracture once the scale effect is recognize
Buckling of laminated glass plates using the effective thickness concept
No full textThe author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The financing support given by the Spanish Ministry of Economy and Competitiveness through the project BIA2014-53774-R is gratefully appreciate
Search for heavy diboson resonances in semileptonic final states in pp collisions at s=13 TeV with the ATLAS detector
No full textThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/
Search for dark matter produced in association with a hadronically decaying vector boson in pp collisions at =13 TeV with the ATLAS detector
No full textSee paper for full list of authors - 10 pages plus author list + cover pages (30 pages total), 5 figures, 2 tables, submitted to PLB, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2015-08/International audienceA search is presented for dark matter produced in association with a hadronically decaying W or Z boson using 3.2 /fb of pp collisions at =13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Events with a hadronic jet compatible with a W or Z boson and with large missing transverse momentum are analysed. The data are consistent with the Standard Model predictions and are interpreted in terms of both an effective field theory and a simplified model containing dark matter
Higgs boson production cross-section measurements and their EFT interpretation in the 4 ℓ decay channel at √s= 13 TeV with the ATLAS detector
No full textHiggs boson properties are studied in the four-lepton decay channel (where lepton = e, μ) using 139 fb - 1 of proton–proton collision data recorded at s=13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio for H→ ZZ∗ decay is measured to be 1.34 ± 0.12 pb for a Higgs boson with absolute rapidity below 2.5, in good agreement with the Standard Model prediction of 1.33 ± 0.08 pb. Cross-sections times branching ratio are measured for the main Higgs boson production modes in several exclusive phase-space regions. The measurements are interpreted in terms of coupling modifiers and of the tensor structure of Higgs boson interactions using an effective field theory approach. Exclusion limits are set on the CP-even and CP-odd ‘beyond the Standard Model’ couplings of the Higgs boson to vector bosons, gluons and top quarks. © 2020, The Author(s)
Measurement of the and production cross sections in multilepton final states using 3.2 fb of collisions at = 13 TeV with the ATLAS detector
No full textSee paper for full list of authors - 22 pages plus author list + cover page (40 pages total), 8 figures, 5 tables. Submitted to Eur. Phys. J. C. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2015-22/International audienceA measurement of the and production cross sections in final states with either two same-charge muons, or three or four leptons (electrons or muons) is presented. The analysis uses a data sample of proton-proton collisions at TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015, corresponding to a total integrated luminosity of 3.2 fb. The inclusive cross sections are extracted using likelihood fits to signal and control regions, resulting in pb and pb, in agreement with the Standard Model predictions
- …
