1,721,844 research outputs found
From Jets to Pixels: Flavour Tagging and Monolithic Pixel Sensors at the FCC-ee
No full textThe FCC-ee is the first stage of a two stage project which would envision a 92 km tunnelbeing used for an electron-positron collider experiment starting around 2045, and a proton-proton collider in the 2070’s. The FCC-ee offers unprecedented precision tests of the StandardModel, owing to its clean leptonic collision environment and exquisite luminosity. The preciseidentification of decay products at future colliders is instrumental to the exploitation of the fullphysics potential. In this thesis two facets of this problem are explored: jet flavour tagging andcharged particle tracking.Jet flavour tagging describes the algorithmic identification of the initiating parton fromhadronic decays. The prospect of identifying strange quark jets has emerged as a promisingavenue to study a multitude of largely unexplored processes, including Z → s¯s production andrare Higgs boson decays. DeepJetTransformer is a transformer-based multiclassifier neural net-work developed by the CMS jet tagging team at the VUB, achieving state-of-the-art performancewhile being relatively lightweight. This thesis combines DeepJetTransformer with secondary ver-texing and a novel implementation of K-short reconstruction at the FCC-ee to identify strangejets. Through the inclusion of different levels of K±/π± discrimination, strange tagging efficien-cies ranging from 31.6% to 57.8% were obtained at a u, d jet efficiency of 10%, highlighting theneed for charged Kaon discrimination at future colliders.Monolithic Active Pixel Sensors (MAPS) combine the sensing node and readout circuitry intothe same substrate, thus offering several advantages with respect to their hybrid counterparts.The Circuit Exploratoire 65 nm (CE-65), and its evolution CE-65v2, are MAPS test structuresproduced in the 65 nm TPSCo CMOS process to explore charge collection properties for avariety of configurations, including variations in pixel pitch, process modification, amplificationscheme, and matrix geometry. In this thesis the lab characterisation of the CE-65v1 and CE-65v2 chips is reported, where charge collection efficiencies of 96% were achieved for all variants.In a subsequent beam test at CERN SPS a sub 3 μm spatial resolution was obtained for Standardprocess variants, satisfying FCC-ee requirements. The characterisation of the CE-65 family ofchips has supplemented the APTS and DPTS studies in the validation of the 65 nm TPSCoprocess as a candidate technology for advanced particle detection applications, directly informingthe development of future tracking detector
Precision Measurement of Strange Quark Asymmetry and Monolithic Pixel Sensors for Vertexing at the FCC-ee
No full textFuture e+e− colliders, such as the FCC-ee, aim to test the Standard Model to the ultimateprecision. This requires synergistic progress in detector technology and data analysis techniques.This thesis comprehensively presents the interlinked efforts targeting these goals.Jet flavour identification algorithms play a crucial role in maximally exploiting the physicspotential of the FCC-ee, particularly in the Higgs and electroweak sectors. The DeepJet-Transformer algorithm, exploiting a transformer-based neural network that is substantiallyfaster to train than state-of-the-art graph neural networks, combines particle-flow reconstruc-tion with advanced vertex reconstruction and hadron particle identification. Beyond an excellentb- and c-jet discrimination, an s-jet tagging efficiency of 40% can be achieved with a 10% ud-jetbackground efficiency. The impact of K±/π± discrimination with varying efficiencies and inclu-sion of reconstructed V0s for strange tagging performance is shown. Similarly, the importanceof charged jet constituents and reconstructed secondary vertices for bottom and charm taggingis presented. The bottom and charm tagging efficiencies were largely uniform over the entiremomentum and polar angle range of interest. However, the strange tagging efficiency showed adependence on the K± and V0 multiplicities in different momentum regimes.A 5σ discovery significance can be achieved while isolating Z → s¯s events from the exclusivedecays of the Z boson with an integrated luminosity of 60 nb−1 of e+e− collisions at √s =91.2 GeV, corresponding to less than a second of the FCC-ee run plan at the Z boson resonance.The improved strange tagging performance opens new avenues for extracting quark-specificasymmetries, such as the forward-backward asymmetry (AFB). Using advanced neural network-based strange tagging and quark-antiquark jet separation with jet charge, the AFB measurementin the strange decay channel of the Z boson is possible with an absolute statistical precisionof 2.6 · 10−6 at the FCC-ee, considering a luminosity of 125 ab−1 at the Z resonance. Thecorresponding sin2 θW value can be measured with an absolute statistical precision of 4.6 · 10−6.To support these improvements, ultra-thin, high-resolution, and robust vertex detectors areessential. Recent advancements in the use of ultra-light monolithic active pixel sensors (MAPS),developed in the 65 nm imaging process, for the ALICE ITS3 project by an international consor-tium of the ALICE collaboration and the CERN EP R&D project envision drastic improvementsin vertexing performance. Process modification is introduced by adding a deep low-dose n-typelayer, which aids in the depletion of full sensor volume by extending the depletion region later-ally while keeping a low sensor capacitance. It leads to faster charge collection and reduction incharge shared with neighbouring pixels, thus improving the detection efficiency.Pixel response calibration and energy resolution measurements performed with the 55Fe ra-dioactive source in the controlled laboratory environment are presented. Four variants of pixelgeometry were tested with a small-scale analogue prototype, APTS, all showing over 99% chargecollection efficiency for a small reverse bias voltage of 1.2 V. The impact of geometry variationon detection efficiency, spatial resolution, and radiation tolerance is highlighted. In-pixel effi-ciency studies show that the loss of efficiency at high thresholds is primarily concentrated at theedges and corners of the pixels. APTS shows sub-3 μm spatial resolution and > 99% detectionefficiency, even under moderate irradiation, satisfying the stringent requirements of ALICE andfuture collider environments.Together, these developments highlight the integrated advancements in detector design, re-construction algorithms, and physics potential, strengthening the next generation of precisionmeasurements at the FCC-ee and beyond
Long-Lived Axion-Like Particles at the Future Circular Electron-Positron Collider
No full textAs the leading theory in particle physics, the Standard Model (SM) defines our understanding of the subatomic world. However, observed phenomena have proven that the SM, despite its great success, is not complete yet and the search for particles Beyond the Standard Model (BSM) has surged ever since. In models that try to address the problems of the SM, BSM long-lived particles (LLPs), which have longer lifetimes than unstable SM particles, occur naturally. With a proposed circular electron-positron collider, the FCC-ee, these BSM LLPs could be discovered.This thesis focuses specifically on the production and detection of long-lived axion-like particles (ALPs), which are well-motivated BSM particles and also possible dark matter candidates. Utilizing the e+e− → Z → aγ → γγγ channel, which only depends on the ALP-photon coupling cγγ under certain assumptions, the sensitivity of the FCC-ee to detect ALPs is examined. Employing the analysis framework of the Future Circular Collider (FCC), the simulation and analysis of events for ALP production were conducted, testing coupling constants ranging from 10−6 to 1.6 and ALP masses between 0.01 GeV and 30 GeV. Finally, the sensitivity of the FCC-ee to a long-lived ALP signature is studied for various settings of the ALP parameters
Triggering and Data Scouting on compressed dark matter models at the CMS experiment
No full textCompressed mass spectra models with low transverse momentum displaced leptons signature have low sensitivity for direct detection at the CMS experiment due to hard trigger constraints. It has been shown in this work that the search significance is obtained over lepton displacements of O(0.1cm) to O(100cm) by lowering the trigger pT threshold on the leptons to 20 GeV. The CMS experiment was undergoing an upgrade during the LHC LS2 and was under preparation for Run 3. New triggers were created for standard data collection streams of the CMS experiment in LHC Run 3 targeting displaced leptons with low-pT threshold on leptons. The new triggers explore isolation, shower shape and delay in the energy deposition in the electromagnetic calorimeter for electrons. The pT threshold on the final states μμ and μe is lowered to 20 GeV while for ee is lowered to 25 and 12 GeV for the two highest energy electrons in the event respectively. Additionally, for events with additional activity such as missing energy or the presence of a jet, the threshold for electrons can be as low as 10 GeV. Additionally, the data scouting in the CMS experiment has been enhanced in the Run 3 of the LHC to include low energy electrons (e) and photons (γ) that allow us to lower the pT threshold without any additional constraints. Events with single e/γ pT threshold of 30 GeV and asymmetric di-e/γ pT threshold of 16 GeV and 12 GeV have been stored. The standard model particles - J/ψ and Υ meson were observed in the di-electron invariant mass distribution along with the peak for the Z boson. This is the first ever result of its kind in the CMS collaboration and opens the possibility to perform low energy searches with the electrons and photons in the scouting data collected by the CMS collaboration in Run 3
Search for Standard Model Production of Four Top Quarks in Compact Muon Solenoid Detector and Designing Neural Networks for Top Quark Yukawa Coupling Measurement from Four Top Quark Production
No full textThe production of four top quarks has been predicted by the Standard Model(SM) and has been considered as one of its important tests. The measurementsobtainable from this production, such as its cross section, can be comparedwith predictions provided by SM. This comparison can determine whether SMis adequate to explain this phenomenon. The four-top quark production is alsosensitive to the coupling strength between the top quark and the Higgs boson, alsoknown as the top Yukawa coupling. By considering Feynman diagrams for thisproduction, this coupling value affects both its cross section and the kinematics ofthe top quarks within the production. These changes caused by top Yukawa couplingoffer potential new information for novel techniques, such as neural networks, tomeasure the coupling value. This dissertation describes the combination of four-topquark production searches in different final states, along with a study of the use ofneural networks for the measurement of top quark Yukawa coupling
From Detector Development to New Physics Searches: CMS HGCAL Validation and Search for Top-Philic Resonances Using Variable-Radius Jet Tagging
No full textThis thesis presents two research works carried out within the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC): the system validation of the scintillator section of the High Granularity Calorimeter (HGCAL), and a search for a heavy resonance coupling to top quarks and produced in association with top quark pairs in proton–proton collisions at center-of-mass energies of 13 and 13.6 TeV. For the High-Luminosity LHC (HL-LHC) phase, the endcap calorimeters of CMS will be replaced by the HGCAL, a high-precision sampling calorimeter designed to cope with the extreme radiation and pileup conditions expected at the HL-LHC. In regions where radiation levels remain moderate, the hadronic section employs scintillator tiles coupled to silicon photomultipliers (SiPM-on-tile) as active materials. Each HGCAL tilemodule, the basic detector unit of this region, accommodates up to 144 SiPM-on-tile channels read out by dedicated front-end electronics. The performance of several tilemodules was evaluated during test-beam campaigns at the DESY-II facility using 3 GeV electron beams. The measurements serve to validate the response and uniformity of the detector components and to confirm that they meet the design specifications for HL-LHC operation. A search for a new heavy resonance that couples exclusively to top quarks and is produced in association with a top quark pair is presented. The analysis uses proton–proton collision data collected with the CMS detector at center-of-mass energies of 13 TeV (2016–2018) and 13.6 TeV (2022). The search targets the final state with two oppositely charged leptons from the W boson decays of the nonresonant top quarks, and two high-energy jets reconstructing the hadronically decaying resonant top quarks. In this scenario, the two top quarks from the resonance decay are expected to be highly Lorentz-boosted. Their hadronic decays are reconstructed using jets clustered with a variable-radius algorithm and identified with a dedicated top quark tagger based on a boosted decision tree (BDT). Events are selected in a final state containing opposite-sign leptons and b-tagged jets, and the resonance mass is reconstructed from pairs of tagged top jets. The analysis probes resonance masses between 500 GeV and 4 TeV and searches for local excesses in the reconstructed mass spectrum. The results are interpreted in the context of models with vector-like, scalar and pseudoscalar resonances produced in association with top quarks, representing the first such interpretation performed with CMS data
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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