Download or read book First Simultaneous Measurement of Single and Pair Production of Top Quarks in Association with a Z Boson at the LHC written by Federica Cecilia Colombina and published by . This book was released on 2024 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Towards Global Interpretation of LHC Data written by Toni Mäkelä and published by Springer Nature. This book was released on 2023-05-16 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the first global interpretation of measurements of jet and top quark production at the Large Hadron Collider, including a simultaneous extraction of the standard model parameters together with constraints on new physics, unbiased from the assumptions on the standard model parameters. As a long-standing problem, any hadron collider search for new physics depends on parton distribution functions, which cannot be predicted but are extracted experimentally. However, performing the extraction in the same kinematic region where physics beyond the standard model is expected to manifest causes the risk of absorbing the new physics effects into the parton distributions. In this book, the issue is addressed by extending the standard model by effective contributions from quark contact interactions describing new physics and extracting the parton distributions and standard model parameters simultaneously with setting limits on the contact interactions. In the process, the most precise single measurement of the strong coupling constant at the LHC is performed, to date. Furthermore, the book details the first investigation of the mass renormalization scale dependence of the top quark mass, highlighting the importance of a proper scale choice for obtaining robust predictions and improving the precision of experimental analyses. The initial chapters provide the reader with a succinct yet accessible introduction to the relevant theoretical and experimental topics. The presented investigations are at the edge of precision in the phenomenology of high-energy physics and serve to pave the road toward a global interpretation of LHC data.

Download or read book Top Quark Pair Production written by Anna Christine Henrichs and published by Springer Science & Business Media. This book was released on 2013-10-04 with total page 231 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Top Quark Pair Production Cross Sections and Calibration of the Top Quark Monte Carlo Mass written by Jan Kieseler and published by Springer. This book was released on 2016-06-15 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Discovery of Single Top Quark Production written by Dag Gillberg and published by Springer Science & Business Media. This book was released on 2011-01-22 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt: The top quark is by far the heaviest known fundamental particle with a mass nearing that of a gold atom. Because of this strikingly high mass, the top quark has several unique properties and might play an important role in electroweak symmetry breaking—the mechanism that gives all elementary particles mass. Creating top quarks requires access to very high energy collisions, and at present only the Tevatron collider at Fermilab is capable of reaching these energies. Until now, top quarks have only been observed produced in pairs via the strong interaction. At hadron colliders, it should also be possible to produce single top quarks via the electroweak interaction. Studies of single top quark production provide opportunities to measure the top quark spin, how top quarks mix with other quarks, and to look for new physics beyond the standard model. Because of these interesting properties, scientists have been looking for single top quarks for more than 15 years. This thesis presents the first discovery of single top quark production. It documents one of the flagship measurements of the D0 experiment, a collaboration of more than 600 physicists from around the world. It describes first observation of a physical process known as “single top quark production”, which had been sought for more than 10 years before its eventual discovery in 2009. Further, his thesis describes, in detail, the innovative approach Dr. Gillberg took to this analysis. Through the use of Boosted Decision Trees, a machine-learning technique, he observed the tiny single top signal within an otherwise overwhelming background. This Doctoral Thesis has been accepted by Simon Fraser University, Burnaby, BC, Canada.

Download or read book Erratum to written by and published by . This book was released on 2015 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: We study top quark pair production in association with a Z boson at the Large Hadron Collider (LHC) and investigate the prospects of measuring the couplings of top quarks to the Z boson. To date these couplings have not been constrained in direct measurements. Such a determination will be possible for the first time at the LHC. Our calculation improves previous coupling studies through the inclusion of next-to-leading order (NLO) QCD corrections in production and decays of all unstable particles. We treat top quarks in the narrow-width approximation and retain all NLO spin correlations. To determine the sensitivity of a coupling measurement we perform a binned log-likelihood ratio test based on normalization and shape information of the angle between the leptons from the Z boson decay. The obtained limits account for statistical uncertainties as well as leading theoretical systematics from residual scale dependence and parton distribution functions. We use current CMS data to place the first direct constraints on the ttbZ couplings. We also consider the upcoming high-energy LHC run and find that with 300 inverse fb of data at an energy of 13 TeV the vector and axial ttbZ couplings can be constrained at the 95% confidence level to C_V=0.24^{+0.39}_{-0.85} and C_A=-0.60^{+0.14}_{-0.18}, where the central values are the Standard Model predictions. This is a reduction of uncertainties by 25% and 42%, respectively, compared to an analysis based on leading-order predictions. We also translate these results into limits on dimension-six operators contributing to the ttbZ interactions beyond the Standard Model.

Download or read book Measurement of the Top Quark Mass Using Single Top Quark Events in Proton proton Collisions at sqrt s written by and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A measurement of the top quark mass is reported in events containing a single top quark produced via the electroweak t channel. The analysis is performed using data from proton-proton collisions collected with the CMS detector at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The top quark is reconstructed from its decay to a W boson and a b quark, with the W boson decaying leptonically to a muon and a neutrino. The specific topology and kinematic properties of single top quark events in the t channel are used to enhance the purity of the sample, suppressing the contribution from top quark pair production. A fit to the invariant mass distribution of reconstructed top quark candidates yields a value of the top quark mass of 172.95 +/- 0.77 (stat) +0.97/-0.93 (syst) GeV. This result is in agreement with the current world average, and represents the first measurement of the top quark mass in event topologies not dominated by top quark pair production.

Download or read book First Measurement of the Cross Section for Top Quark Pair Production in Proton Proton Collisions at sqrt s written by and published by . This book was released on 2011 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first measurement of the cross section for top-quark pair production in pp collisions at the LHC at center-of-mass energy sqrt(s)= 7 TeV has been performed using 3.1 {\pm} 0.3 inverse pb of data recorded by the CMS detector. This result utilizes the final state with two isolated, highly energetic charged leptons, large missing transverse energy, and two or more jets. Backgrounds from Drell-Yan and non-W/Z boson production are estimated from data. Eleven events are observed in the data with 2.1 {\pm} 1.0 events expected from background. The measured cross section is 194 {\pm} 72 (stat.) {\pm} 24 (syst.) {\pm} 21 (lumi.) pb, consistent with next-to-leading order predictions.

Download or read book Measurements of the Top Quark Pair Production Cross Section and Branching Ratio to a W boson and Bottom Quark Using the Semi leptonic and Dilepton Final States with the ATLAS Detector at the LHC written by Robert E. Calkins and published by . This book was released on 2012 with total page 241 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract : In the Standard Model, the top quark plays a unique role as the heaviest known fundamental particle and as a quark that decays before it is able to hadronize. Top quarks are expected to decay to a W-boson and a b-quark nearly 100% of the time. If the branching ratio of t → Wb is lower than one, the distribution of the number of b-tagged jets will shift to lower multiplicities. A simultaneous likelihood fit to the number of b-tagged jets distributions in the lepton+jets and dilepton channels is performed on 4.7 fb−1 of data collected by the ATLAS detector to extract both the branching ratio and the tt ̄ cross section. The branching ratio of t → Wb, R, is measured to be 1.06±0.11, which is consistent with the Standard Model value. This is the first measurement of the t → Wb branching ratio performed with the ATLAS detector using both the lepton+jets and dilepton channels at the LHC. The tt ̄ cross section is measured to be [special characters omitted] pb, which agrees with NNLO predictions.

Download or read book First Measurement of the Top quark Pair Production Cross Section in Proton proton Collisions at the Center of Mass Energy of 7 TeV written by Puneeth D. Kalavase and published by . This book was released on 2011 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first measurement of the cross section for top-quark pair production in proton-proton collisions at the Large Hadron Collider at center-of-mass energy of 7 TeV has been performed using a data sample corresponding to an integrated luminosity of 3 pb-1 recorded by the CMS detector. This result utilizes the final state with two isolated, highly energetic charged leptons, large missing transverse energy, and two or more jets. Backgrounds from Drell-Yan and non-W/Z boson production are estimated from data. Eleven events are observed in the data with 2.1+/-1.0 events expected from background. The measured cross section is 194+/-72 (statistical) +/-24 (systematic) +/-21 (luminosity) pb. The result is consistent with next-to-leading order theoretical predictions.

Download or read book Measurement of Top Quark antiquark Pair Production in Association with a W Or Z Boson in Pp Collisions at sqrt s written by and published by . This book was released on 2014 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: A measurement of the cross section for the production of top quark-antiquark pairs (${\mathrm {t}}\overline{{\mathrm {t}}}$) in association with a vector boson V (W or Z) in proton-proton collisions at $\sqrt{s} = 8$ $\, \text {TeV}$ is presented. The results are based on a dataset corresponding to an integrated luminosity of 19.5 fb$^{-1}$ recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and $\mu$) channels: a same-sign dilepton analysis targeting ${\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W} $ events, and trilepton and four-lepton analyses designed for ${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}} $ events. In the same-sign dilepton channel, the ${\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W} $ cross section is measured as $\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W}} = 170 ^{+90-80}\, \text {(stat)} \pm 70\, \text {(syst)} \, \text {fb} $, corresponding to a significance of 1.6 standard deviations over the background-only hypothesis. Combining the trilepton and four-lepton channels, a direct measurement of the ${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}} $ cross section, $\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}}} = 200 ^{+80-70}\, \text {(stat)} ^{+40-30}\, \text {(syst)} \mathrm{fb}^{-1} $, is obtained with a significance of 3.1 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive ${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {V}} $ process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.

Download or read book First Measurement of the Running of the Top Quark Mass written by Matteo M. Defranchis and published by Springer Nature. This book was released on 2022-01-03 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, the first measurement of the running of the top quark mass is presented. This is a fundamental quantum effect that had never been studied before. Any deviation from the expected behaviour can be interpreted as a hint of the presence of physics beyond the Standard Model. All relevant aspects of the analysis are extensively described and documented. This thesis also describes a simultaneous measurement of the inclusive top quark-antiquark production cross section and the top quark mass in the simulation. The measured cross section is also used to precisely determine the values of the top quark mass and the strong coupling constant by comparing to state-of-the-art theoretical predictions. All the theoretical and experimental aspects relevant to the results presented in this thesis are discussed in the initial chapters in a concise but complete way, which makes the material accessible to a wider audience.

Download or read book Search for Scalar Top Quarks and Higgsino Like Neutralinos written by Takuya Nobe and published by Springer. This book was released on 2015-11-30 with total page 229 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reports a search for theoretically natural supersymmetry (SUSY) at the Large Hadron Collider (LHC). The data collected with the ATLAS detector in 2012 corresponding to 20 /fb of an integrated luminosity have been analyzed for stop pair production in proton–proton collisions at a center-of-mass energy of 8 TeV at the Large Hadron Collider (LHC) in the scenario of the higgsino-like neutralino. The author focuses on stop decaying into a bottom quark and chargino. In the scenario of the higgsino-like neutralino, the mass difference between charginos and neutralinos (Δm) is expected to be small, and observable final-state particles are likely to have low-momentum (soft). The author develops a dedicated analysis with a soft lepton as a probe of particles from chargino decay, which suppresses the large amount of backgrounds. As a result of the analysis, no significant SUSY signal is observed. The 95% confidence-level exclusion limits are set to masses of stop and neutralino assuming Δm = 20 GeV. The region with ΔM (the mass difference between stop and neutralino) 70 GeV is excluded for the first time at stop mass of less than 210 GeV. The author also excludes the signals with ΔM 120 GeV up to 600 GeV of stop mass with neutralino mass of less than 280 GeV. The author clearly shows very few remaining parameter spaces for light stop (e.g., topology of stop decay is extremely similar to the SM top quark) by combining his results and previous ATLAS analyses. His results provide a strong constraint to searches for new physics in the future.

Download or read book Physics at the Large Hadron Collider written by Amitava Datta and published by Springer Science & Business Media. This book was released on 2010-05-30 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: In an epoch when particle physics is awaiting a major step forward, the Large Hydron Collider (LHC) at CERN, Geneva will soon be operational. It will collide a beam of high energy protons with another similar beam circulation in the same 27 km tunnel but in the opposite direction, resulting in the production of many elementary particles some never created in the laboratory before. It is widely expected that the LHC will discover the Higgs boson, the particle which supposedly lends masses to all other fundamental particles. In addition, the question as to whether there is some new law of physics at such high energy is likely to be answered through this experiment. The present volume contains a collection of articles written by international experts, both theoreticians and experimentalists, from India and abroad, which aims to acquaint a non-specialist with some basic issues related to the LHC. At the same time, it is expected to be a useful, rudimentary companion of introductory exposition and technical expertise alike, and it is hoped to become unique in its kind. The fact that there is substantial Indian involvement in the entire LHC endeavour, at all levels including fabrication, physics analysis procedures as well as theoretical studies, is also amply brought out in the collection.

Download or read book Simultaneous Measurement of the Top Quark Pair Production Cross section and Rb in the ATLAS Experiment written by Jordi Nadal Serrano and published by . This book was released on 2012* with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: L'objectiu d'aquesta tesi és mesurar simultàniament la secció eficaç de producció de parelles t ̄t i el coeficient Rb 1 a l'experiment ATLAS de l'LHC, a Ginebra. ATLAS (A Toroidal LHC ApparatuS) és un dels quatre grans experiments que dur a terme noves investigacions sobre la matèria, l'energia i el temps en funcionament al Gran Col·lisionador d'Hadrons (LHC) al CERN. ATLAS va ser dissenyat per entendre perquè l'Univers és tal com ́es avui en dia. ́És capac ̧ d'examinar els constituents més íntims de la matèria més enllà del que ho ha fet mai cap altre experiment i així poder explorar nous fenòmens fonamentals. Els descobriments dels secrets de la natura mitjançant les col·lisions de partícules dins del detector ATLAS és un desafiament científic i tecnològic sense precedents a la història. El detector ATLAS és de gran complexitat, essent el detector més gran mai construït dins el camp de la física de partícules. Hi ha diversos processos físics que tenen estats finals similars a la desintegració del top (bàsicament un leptó, quatre jets i energia transversa perduda (MET)) que considerem com a senyal. Com per exemple, la desintregració dels bosons W i Z a estats finals amb leptons i jets, esdeveniments de QCD que estan formats pràcticament de jets i MET, etc. Una bona identificació per una posterior eliminació d'aquests processos no interessants és de vital importancia per estimar amb una gran precisió els nostres esdeveniments de senyal. Un cop tenim la selecció del nostre senyal optimitzada per obtenir la màxima puressa de quarks top podem començar a fer la mesura de la secció eficaç de producció. Aquesta es fa mitjançant un "fit" a la distribució de la massa reconstruïda del top hadrònic. Aprofitant la gran correlació que hi ha entre la secció eficac i el paràmetre de la matriu CKM (Vtb) hem inclòs aquest últim al fit, donant l'opció de buscar un límit per nova física. Per millorar els errors sistemàtics (amb 35 pb−1 era 10% a la secció eficaç) també incloem al fit els mateixos errors deixant-los lliures i són les propies dades les que redueixien l'error (amb 1 fb−1 serà 6% a la secció eficaç). Així doncs amb les dades que disposem ( 1 fb−1) podrem aconseguir la mesura més precisa (a data d'avui) per la secció eficaç del top quark i el factor Rb que dóna molt espai per interpretacions de nova física.

Download or read book Measurement of Bottom Quark Pair Production in Association with Z Bosons and Top Quarks with the ATLAS Detector written by Stewart Swift (Ph. D. in physics) and published by . This book was released on 2019 with total page 223 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Measurement of the Single Top TW Associated Production Cross Section at 7 TeV with 4 9 Fb 1 of Data in the Dilepton Decay Channel at the LHC Using the CMS Detector written by William Patrick Martin and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The first measurement of the production cross section for a single top quark in association with a W boson with the CMS experiment at the Large Hadron Collider is presented. The analysed data is from proton-proton collisions at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 4.9 fb-1. The analysis focuses on the leptonic final states of the process and implements a cut-based method. The final state consists of two leptons, two neutrinos and a jet from the fragmentation of a b-quark. The primary source of background events arises from tt(overbar) production, followed by Z/gamma* processes. The observed signal has a significance of 3:5sigma and corresponds to a cross section measurement of 14:9+5:0 -5:1 (stat + syst) pb, in agreement with the Standard Model expectations.