Bachacou, Henri
Fermi National Accelerator Lab., Batavia, IL (United States). Funding organisation: US Department of Energy (United States)
arXiv e-print [ PDF ]2005
Fermi National Accelerator Lab., Batavia, IL (United States). Funding organisation: US Department of Energy (United States)
arXiv e-print [ PDF ]2005
AbstractAbstract
[en] We present measurements of the top-antitop production cross section in b-tagged lepton + jets events from proton-antiproton collisions at 1.96 TeV using the CDF detector at Fermilab. B-jets are tagged with either a secondary vertex algorithm, or a soft lepton tagger that identifies muons from B hadron semileptonic decays. With Tevatron Run II data, we estimate the top-antitop signal fraction in two different ways: by estimating the various background contributions, and by fitting directly the leading jet transverse energy spectrum for the signal and background contributions. A subset of the sample with two secondary vertex tagged jets yields a production cross section consistent with the inclusive measurements. Results are consistent with a Standard Model top-antitop signal and current measurements of the top quark mass
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1 Jan 2005; 3 p; DPF 2004: Annual Meeting of the Division of Particles and Fields (DPF) of the American Physical Society (APS); Riverside, CA (United States); 26-31 Aug 2004; ARXIV EPRINT NUMBER HEP-EX--0501007; AC02-76CH03000; Available from http://lss.fnal.gov/cgi-bin/find_paper.pl?conf-04-448-E.pdf; PURL: https://www.osti.gov/servlets/purl/15020287-HOuFvt/; Int.J.Mod.Phys.A20:3180,2005
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ACCELERATORS, CYCLIC ACCELERATORS, DECAY, ELEMENTARY PARTICLES, ENERGY, FERMIONS, FIELD THEORIES, GRAND UNIFIED THEORY, KINETIC ENERGY, LEPTONS, MATHEMATICAL MODELS, MEASURING INSTRUMENTS, NATIONAL ORGANIZATIONS, PARTICLE DECAY, PARTICLE MODELS, POSTULATED PARTICLES, QUANTUM FIELD THEORY, QUARKS, RADIATION DETECTORS, SYNCHROTRONS, TOP PARTICLES, UNIFIED GAUGE MODELS, US DOE, US ORGANIZATIONS, WEAK PARTICLE DECAY
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Bachacou, Henri
Universite de Paris VI, 4 Pl. Jussieu, 75005 Paris (France); CEA, DSM-IRFU (France)2017
Universite de Paris VI, 4 Pl. Jussieu, 75005 Paris (France); CEA, DSM-IRFU (France)2017
AbstractAbstract
[en] As convener of the Exotics group at the very beginning of the LHC operations, I contributed to developing a comprehensive program of searches for phenomena beyond the Standard Model (BSM). In Chapter 2, I give a brief overview of this vast program and review the most important results. In ATLAS, Supersymmetry is studied in a group distinct from the Exotics group; for completeness I also describe succinctly the strategy and the recent results of the search for Supersymmetry. Given the great diversity of BSM models and the experimental signatures they lead to, a methodical strategy had to be put in place, with the priority given to the observation of any deviation from the Standard Model, independently of the underlying cause for such a deviation: the emphasis was put on analyses that cover a wide range of models rather than being optimized for a specific one. As much as possible, all experimental signatures were explored, independently of their theoretical motivation. Chapter 3 describes a specific BSM search to which I contributed directly and is based on an ATLAS article that was published in 2015: the search for vector-like quarks (VLQ) produced in pair and involving a Higgs boson in their decay. I focused on the case of a pair of bottom-like heavy quarks decaying to bHbH that had been neglected in previous analyses. In Chapter 4, I describe two personal contributions to the identification of b-jets: soft-muon b-tagging, and the calibration of the b-tagging algorithms performance using top-antitop events. Soft-muon b-tagging makes use of the presence of a relatively large-momentum muon coming from the semi-leptonic decay of B hadrons in b-jets. Joining my expertise in b-tagging acquired during my PhD and the expertise of the Saclay group in muon reconstruction, I developed the first soft-muon tagger in ATLAS and commissioned it with the very first data accumulated in 2009. In parallel I worked on the first studies of techniques of calibration of the b-tagging performance using data. The large top pair production cross-section at the LHC permits to accumulate a large top pair control sample. Thanks to the well-known heavy flavor content in those events (two b-jets in each event, at tree level), the b-tagging efficiency can be measured in data with great precision and over a large range of jet momentum. I developed a technique that was able to give first results with very low integrated luminosity. The same technique is applied today, with large integrated luminosity, to measure the top pair production cross-section with in situ calibration of the b-tagging efficiency, thus removing the dominant systematic uncertainty from b-tagging and leading to the most precise measurement of this quantity. This work was described in two ATLAS public documents. Finally in Chapter 5, I discuss the future prospects of BSM searches at the LHC as well as my personal research projects. (author)
[fr]
En tant que responsable du groupe Exotics au tout debut de l'exploitation du LHC, j'ai contribue a l'elaboration d'un programme complet de recherche de phenomenes au-dela du modele standard (BSM). Dans le chapitre 2, je donne un bref apercu de ce vaste programme et je passe en revue les resultats les plus importants. Dans ATLAS, la supersymetrie est etudiee dans un groupe distinct du groupe Exotique; par souci d'exhaustivite, je decris aussi succinctement la strategie et les resultats recents de la recherche de la supersymetrie. Etant donne la grande diversite des modeles BSM et des signatures experimentales auxquelles ils conduisent, une strategie methodique a du etre mise en place, avec la priorite donnee a l'observation de toute deviation du Modele Standard, independamment de la cause sous-jacente de cette deviation: l'accent a ete mis sur des analyses qui couvrent un large eventail de modeles plutot que d'etre optimisees pour un modele specifique. Dans la mesure du possible, toutes les signatures experimentales ont ete explorees, independamment de leur motivation theorique. Le chapitre 3 decrit une recherche BSM specifique a laquelle j'ai directement contribue et qui est basee sur un article ATLAS publie en 2015: la recherche de quarks vectoriels (VLQ) produits en paire et impliquant un boson de Higgs dans leur desintegration. Je me suis concentre sur le cas d'une paire de quarks lourds de type bottom se desintegrant en bHbH qui avait ete neglige dans les analyses precedentes. Dans le chapitre 4, je decris deux contributions personnelles a l'identification des jets b: le b-tagging de muons mous et l'etalonnage des performances des algorithmes de b-tagging a l'aide d'evenements top-antitop. Le b-tagging par muon mou utilise la presence d'un muon a relativement grand moment provenant de la desintegration semi-leptonique des hadrons B dans les b-jets. En combinant mon expertise en b-tagging acquise pendant mon doctorat et l'expertise du groupe de Saclay dans la reconstruction des muons, j'ai developpe le premier soft-muon tagger dans ATLAS et l'ai mis en service avec les toutes premieres donnees accumulees en 2009. Parallelement, j'ai travaille sur les premieres etudes des techniques d'etalonnage des performances du b-tagging a l'aide de donnees. L'importante section efficace de production de paires superieures au LHC permet d'accumuler un large echantillon de controle de paires superieures. Grace au contenu bien connu en saveurs lourdes dans ces evenements (deux jets b dans chaque evenement, au niveau de l'arbre), l'efficacite du b-tagging peut etre mesuree dans les donnees avec une grande precision et sur une large gamme d'elan du jet. J'ai mis au point une technique qui a permis d'obtenir les premiers resultats avec une luminosite integree tres faible. La meme technique est appliquee aujourd'hui, avec une grande luminosite integree, pour mesurer la section transversale de production de paires superieures avec une calibration in situ de l'efficacite du b-tagging, eliminant ainsi l'incertitude systematique dominante du b-tagging et conduisant a la mesure la plus precise de cette quantite. Ce travail a ete decrit dans deux documents publics ATLAS. Enfin, dans le chapitre 5, je discute des perspectives futures des recherches BSM au LHC ainsi que de mes projets de recherche personnelsOriginal Title
A la recherche de phenomenes au-dela du modele standard avec l'experience ATLAS au LHC
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8 Jun 2017; 139 p; 199 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Physique des Particules; HDR: Memoire d'Habilitation a Diriger des Recherches
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Bachacou, Henri
Fermi National Accelerator Lab., Batavia, IL (United States). Funding organisation: US Department of Energy (United States)2004
Fermi National Accelerator Lab., Batavia, IL (United States). Funding organisation: US Department of Energy (United States)2004
AbstractAbstract
[en] This thesis presents a measurement of the t(bar t) production cross section at CDF using the 162 pb-1 of data taken at the Tevatron between February 2002 and September 2003. It is organized as follows: Chapter 2 is a brief introduction to quantum field theory, the Standard Model, and top quark physics, as well as an overview of the analysis, and the motivation for it. Chapter 3 describes the experimental setup: the chain of accelerators, the Tevatron collider, and the Collider Detector at Fermilab (CDF). Chapter 4 describes the event reconstruction, the data samples, and the event selection. Chapter 5 goes into the details of the secondary vertex b-tagging algorithm. Chapter 6 describes the measurement of the b-tagging algorithm efficiency and fake rate. Chapter 7 describes the estimation of the heavy flavor composition of the W + Jets sample, necessary to understand the background due to W + Heavy Flavor production. Chapter 8 describes the estimate of the various backgrounds. Chapter 10 shows Z0 + Jets and W + Jets data samples used for this analysis and gives the result of the measurement. Chapter 11 discusses the result and concludes on the prospects of top quark physics. A derivation of the method used to measure the b-tagging algorithm efficiency is given in Appendix A. A list of the candidate events together with some of their characteristics is given in Appendix B. Appendix C presents a study of a jet algorithm that combines both tracking and calorimeter information in an attempt to improve the jet energy measurement resolution. Appendix D presents the SvxMon software dedicated to monitoring the silicon vertex detector
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1 Dec 2004; 232 p; AC--02-76CH03000; Available from PURL: https://www.osti.gov/servlets/purl/15016943-XHKaQj/native/; Submitted to the Univ. of California, Berkeley, CA (US); Thesis (Ph.D.)
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Miscellaneous
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Thesis/Dissertation
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ACCELERATORS, CYCLIC ACCELERATORS, ELEMENTARY PARTICLES, FERMIONS, FIELD THEORIES, GRAND UNIFIED THEORY, MATHEMATICAL LOGIC, MATHEMATICAL MODELS, MEASURING INSTRUMENTS, PARTICLE MODELS, POSTULATED PARTICLES, QUANTUM FIELD THEORY, QUARKS, RADIATION DETECTORS, SYNCHROTRONS, TOP PARTICLES, UNIFIED GAUGE MODELS
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Bachacou, Henri; Hinchliffe, Ian; Paige, Frank E.
Lawrence Berkeley National Lab., CA (United States). Funding organisation: USDOE Director, Office of Science. Office of High Energy and Nuclear Physics. Division of High Energy Physics (United States)1999
Lawrence Berkeley National Lab., CA (United States). Funding organisation: USDOE Director, Office of Science. Office of High Energy and Nuclear Physics. Division of High Energy Physics (United States)1999
AbstractAbstract
No abstract available
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Physical Review D; v. 62(1); 1 Jul 1999; [vp.]; BNL-HET--99/15; ATL-COM-PHY--99-017; AC03-76SF00098; Available from Lawrence Berkeley National Lab., CA (United States)
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Bachacou, Henri, E-mail: henri.bachacou@cea.fr2012
AbstractAbstract
[en] The LHC has delivered several fb-1 of data in spring and summer 2011, opening new windows of opportunity for discovering phenomena beyond the Standard Model. A summary of the searches conducted by the ATLAS and CMS experiments based on about 1 fb-1 of data is presented. (author)
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25. international symposium on lepton-photon interactions at high energies, Lepton-Photon 2011. Pt. 1; Mumbai (India); 22-27 Jan 2011; 54 refs., 11 figs.
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Journal Article
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Pramana; CODEN PRAMCI; v. 79(4); p. 691-701
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[en] This paper presents new measurements in a case study of the minimal supergravity (SUGRA) model with m0=100 GeV, m1/2=300 GeV, A0=0, tan β=2, and sgn μ=+ based on four-body distributions from three-step decays and on minimum masses in such decays. These measurements allow masses of supersymmetric particles to be determined without relying on a model. The feasibility of testing slepton universality at the ∼0.1% level at high luminosity is discussed. In addition, the effect of enlarging the parameter space of the minimal SUGRA model is discussed. The direct production of left-handed sleptons and the nonobservation of additional structure in the dilepton invariant mass distributions are shown to provide additional constraints. (c) 2000 The American Physical Society
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Journal Article
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Numerical Data
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