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Author: Publisher: ISBN: Category : Languages : en Pages : 218
Book Description
The top quark pair production and decay into leptons with at least one being a [tau] lepton is studied in the framework of the CDF experiment at the Tevatron proton antiproton collider at Fermilab (USA). The selection requires an electron or a muon produced either by the [tau] lepton decay or by a W decay. The analysis uses the complete Run II data set i.e. 9.0 fb-1, selected by one trigger based on a low transverse momentum electron or muon plus one isolated charged track. The top quark pair production cross section at 1.96 TeV is measured at 8.2 ± 1.7+1.2-1.1 ± 0.5 pb, and the top branching ratio into [tau] lepton is measured at 0.120 ± 0.027+0.022 -0.019 ± 0.007 with statistical, systematics and luminosity uncertainties. These are up to date the most accurate results in this top decay channel and are in good agreement with the results obtained using other decay channels of the top at the Tevatron. The branching ratio is also measured separating the single lepton from the two leptons events with a log likelihood method. This is the first time these two signatures are separately identified. With a fit to data along the log-likelihood variable an alternative measurement of the branching ratio is made: 0.098 ± 0.022(stat:) ± 0.014(syst:); it is in good agreement with the expectations of the Standard Model (with lepton universality) within the experimental uncertainties. The branching ratio is constrained to be less than 0.159 at 95% con dence level. This limit translates into a limit of a top branching ratio into a potential charged Higgs boson.
Author: Publisher: ISBN: Category : Languages : en Pages : 218
Book Description
The top quark pair production and decay into leptons with at least one being a [tau] lepton is studied in the framework of the CDF experiment at the Tevatron proton antiproton collider at Fermilab (USA). The selection requires an electron or a muon produced either by the [tau] lepton decay or by a W decay. The analysis uses the complete Run II data set i.e. 9.0 fb-1, selected by one trigger based on a low transverse momentum electron or muon plus one isolated charged track. The top quark pair production cross section at 1.96 TeV is measured at 8.2 ± 1.7+1.2-1.1 ± 0.5 pb, and the top branching ratio into [tau] lepton is measured at 0.120 ± 0.027+0.022 -0.019 ± 0.007 with statistical, systematics and luminosity uncertainties. These are up to date the most accurate results in this top decay channel and are in good agreement with the results obtained using other decay channels of the top at the Tevatron. The branching ratio is also measured separating the single lepton from the two leptons events with a log likelihood method. This is the first time these two signatures are separately identified. With a fit to data along the log-likelihood variable an alternative measurement of the branching ratio is made: 0.098 ± 0.022(stat:) ± 0.014(syst:); it is in good agreement with the expectations of the Standard Model (with lepton universality) within the experimental uncertainties. The branching ratio is constrained to be less than 0.159 at 95% con dence level. This limit translates into a limit of a top branching ratio into a potential charged Higgs boson.
Author: Stéphane Tourneur Publisher: ISBN: Category : Languages : en Pages : 140
Book Description
The search for top quark decays with tau leptons in p/pbar collisions at sqrt(s)=1.96 TeV using the CDF detector has two main goals: To observe one of the last top decay channels yet to be observed and to search for possible excesses over the standard model expectations. The signal is tiny and difficult to extract from a high background dominated by Z->TauTau+2 jets events, and W+3 jets in which a jet is misidentified as a hadronic tau. One of the main original of this work is the development of a rigorous estimation method of the tricky W+jets background in an environment characterized by a high missing transverse energy, one electron or muon, and one hadronic tau. The analysis makes use of two successive data samples with 350/pb and 1/fb of integrated luminosity. After a thorough control of the method, a 92\% signal evidence is established with 1/fb of data. The relative excess of the top in tau signal is also constrained down to R
Author: Anna Christine Henrichs Publisher: Springer Science & Business Media ISBN: 3319014870 Category : Science Languages : en Pages : 231
Book Description
Before any kind of new physics discovery could be made at the LHC, a precise understanding and measurement of the Standard Model of particle physics' processes was necessary. The book provides an introduction to top quark production in the context of the Standard Model and presents two such precise measurements of the production of top quark pairs in proton-proton collisions at a center-of-mass energy of 7 TeV that were observed with the ATLAS Experiment at the LHC. The presented measurements focus on events with one charged lepton, missing transverse energy and jets. Using novel and advanced analysis techniques as well as a good understanding of the detector, they constitute the most precise measurements of the quantity at that time.
Author: Publisher: ISBN: Category : Languages : en Pages : 31
Book Description
The top quark pair production cross section is measured in dilepton events with one electron or muon, and one hadronically decaying tau lepton from the decay t anti-t to (l nu(l)) (tau nu(tau)) b anti-b, where l can be either an electron or a muon. The data sample corresponds to an integrated luminosity of 2.0 inverse femtobarns for the electron channel and 2.2 inverse femtobarns for the muon channel, collected by the CMS detector at the LHC. This is the first measurement of the t anti-t cross section explicitly including tau leptons in proton-proton collisions at sqrt(s)=7 TeV. The measured value sigma(t anti-t) = 143 +/- 14 (stat.) +/- 22 (syst.) +/- 3 (lumi.) pb is consistent with the standard model predictions.
Author: Marcel Rieger Publisher: Springer Nature ISBN: 3030653803 Category : Science Languages : en Pages : 217
Book Description
In 1964, a mechanism explaining the origin of particle masses was proposed by Robert Brout, François Englert, and Peter W. Higgs. 48 years later, in 2012, the so-called Higgs boson was discovered in proton-proton collisions recorded by experiments at the LHC. Since then, its ability to interact with quarks remained experimentally unconfirmed. This book presents a search for Higgs bosons produced in association with top quarks tt̄H in data recorded with the CMS detector in 2016. It focuses on Higgs boson decays into bottom quarks H → bb̅ and top quark pair decays involving at least one lepton. In this analysis, a multiclass classification approach using deep learning techniques was applied for the first time. In light of the dominant background contribution from tt̄ production, the developed method proved to achieve superior sensitivity with respect to existing techniques. In combination with searches in different decay channels, the presented work contributed to the first observations of tt̄H production and H → bb̅ decays.
Author: Jan Kieseler Publisher: Springer ISBN: 3319400053 Category : Science Languages : en Pages : 172
Book Description
This thesis presents the first experimental calibration of the top-quark Monte-Carlo mass. It also provides the top-quark mass-independent and most precise top-quark pair production cross-section measurement to date. The most precise measurements of the top-quark mass obtain the top-quark mass parameter (Monte-Carlo mass) used in simulations, which are partially based on heuristic models. Its interpretation in terms of mass parameters used in theoretical calculations, e.g. a running or a pole mass, has been a long-standing open problem with far-reaching implications beyond particle physics, even affecting conclusions on the stability of the vacuum state of our universe. In this thesis, this problem is solved experimentally in three steps using data obtained with the compact muon solenoid (CMS) detector. The most precise top-quark pair production cross-section measurements to date are performed. The Monte-Carlo mass is determined and a new method for extracting the top-quark mass from theoretical calculations is presented. Lastly, the top-quark production cross-sections are obtained – for the first time – without residual dependence on the top-quark mass, are interpreted using theoretical calculations to determine the top-quark running- and pole mass with unprecedented precision, and are fully consistently compared with the simultaneously obtained top-quark Monte-Carlo mass.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
We discuss tau identification techniques at hadron colliders, and present the measurements and the searches performed so far. We report on top quark pair production in the decay channel containing at least one tau lepton. Also, we present results dedicated to searches for new particles, with taus in the final state. We present a search for the charged Higgs boson in the tau decay channel, as well as for the leptoquark family containing tau leptons. Finally, we indicate the capabilities of detecting and triggering on tau leptons in the future collider run.
Author: Alexander Grohsjean Publisher: Springer Science & Business Media ISBN: 364214070X Category : Science Languages : en Pages : 155
Book Description
The main pacemakers of scienti?c research are curiosity, ingenuity, and a pinch of persistence. Equipped with these characteristics a young researcher will be s- cessful in pushing scienti?c discoveries. And there is still a lot to discover and to understand. In the course of understanding the origin and structure of matter it is now known that all matter is made up of six types of quarks. Each of these carry a different mass. But neither are the particular mass values understood nor is it known why elementary particles carry mass at all. One could perhaps accept some small generic mass value for every quark, but nature has decided differently. Two quarks are extremely light, three more have a somewhat typical mass value, but one quark is extremely massive. It is the top quark, the heaviest quark and even the heaviest elementary particle that we know, carrying a mass as large as the mass of three iron nuclei. Even though there exists no explanation of why different particle types carry certain masses, the internal consistency of the currently best theory—the standard model of particle physics—yields a relation between the masses of the top quark, the so-called W boson, and the yet unobserved Higgs particle. Therefore, when one assumes validity of the model, it is even possible to take precise measurements of the top quark mass to predict the mass of the Higgs (and potentially other yet unobserved) particles.
Author: Luca Cadamuro Publisher: Springer ISBN: 3030040550 Category : Science Languages : en Pages : 273
Book Description
This thesis presents innovative contributions to the CMS experiment in the new trigger system for the restart of the LHC collisions in Run II, as well as original analysis methods and important results that led to official publications of the Collaboration. The author's novel reconstruction algorithms, deployed on the Field-Programmable Gate Arrays of the new CMS trigger architecture, have brought a gain of over a factor 2 in efficiency for the identification of tau leptons, with a very significant impact on important H boson measurements, such as its decays to tau lepton pairs and the search for H boson pair production. He also describes a novel analysis of HH → bb tautau, a high priority physics topic in a difficult channel. The original strategy, optimisation of event categories, and the control of the background have made the result one of the most sensitive concerning the self-coupling of the Higgs boson among all possible channels at the LHC.
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Author: Stéphane Tourneur
Author: Anna Christine Henrichs
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Author: Marcel Rieger
Author: Jan Kieseler
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Author: Alexander Grohsjean
Author: Luca Cadamuro
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