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Measurement of Double-differential Cross Sections for Top Quark Pair Production in Pp Collisions at $\sqrt{s}$

Measurement of Double-differential Cross Sections for Top Quark Pair Production in Pp Collisions at $\sqrt{s}$
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Release: 2017
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Normalized double-differential cross sections for top quark pair (ttbar) production are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 19.7 inverse femtobarns. The measurement is performed in the dilepton e+/- mu-/+ final state. The ttbar cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and ttbar system. The data are compared to calculations using perturbative quantum chromodynamics at next-to-leading and approximate next-to-next-to-leading orders. They are also compared to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall agreement is observed with the predictions, which is improved when the latest global sets of proton parton distribution functions are used. The inclusion of the measured ttbar cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.


Top-Quark Pair Production Cross Sections and Calibration of the Top-Quark Monte-Carlo Mass

Top-Quark Pair Production Cross Sections and Calibration of the Top-Quark Monte-Carlo Mass
Author: Jan Kieseler
Publisher: Springer
Total Pages: 172
Release: 2016-06-15
Genre: Science
ISBN: 3319400053

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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.


Towards Global Interpretation of LHC Data

Towards Global Interpretation of LHC Data
Author: Toni Mäkelä
Publisher: Springer Nature
Total Pages: 173
Release: 2023-05-16
Genre: Science
ISBN: 3031297792

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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.


Measurement of the Inclusive and Differential Cross-sections for Semileptonic Ttbb Production with the CMS Detector at CERN and Studies of the Readout Chip for the Phase 2 Upgrade of the CMS Pixel Detector

Measurement of the Inclusive and Differential Cross-sections for Semileptonic Ttbb Production with the CMS Detector at CERN and Studies of the Readout Chip for the Phase 2 Upgrade of the CMS Pixel Detector
Author: Umberto Molinatti
Publisher:
Total Pages: 0
Release: 2023
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ISBN:

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Measurement of Differential Cross Sections for Top Quark Pair Production Using the Lepton+jets Final State in Proton-proton Collisions at 13 TeV.

Measurement of Differential Cross Sections for Top Quark Pair Production Using the Lepton+jets Final State in Proton-proton Collisions at 13 TeV.
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Release: 2016
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ISBN:

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Differential and double-differential cross sections for the production of top quark pairs in proton-proton collisions at 13 TeV are measured as a function of jet multiplicity and of kinematic variables of the top quarks and the top quark-antiquark system. This analysis is based on data collected by the CMS experiment at the LHC corresponding to an integrated luminosity of 2.3 inverse femtobarns. The measurements are performed in the lepton+jets decay channels with a single muon or electron in the final state. The differential cross sections are presented at particle level, within a phase space close to the experimental acceptance, and at parton level in the full phase space. The results are compared to several standard model predictions.


Measurements of Normalized Differential Cross Sections for Tt{u00AF} Production in Pp Collisions at (s)

Measurements of Normalized Differential Cross Sections for Tt{u00AF} Production in Pp Collisions at (s)
Author:
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Total Pages:
Release: 2014
Genre:
ISBN:

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We present measurements of normalized differential cross sections for top-quark pair production as a function of the top-quark transverse momentum, and of the mass, transverse momentum, and rapidity of the t¯t system, in proton–proton collisions at a center-of-mass energy of √ s=7 TeV. The data set corresponds to an integrated luminosity of 4.6 fb−1, recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton + jets channel, requiring exactly one lepton and at least four jets with at least one of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector efficiency and resolution effects and are compared to several Monte Carlo simulations and theory calculations. The results are in fair agreement with the predictions in a wide kinematic range. Nevertheless, data distributions are softer than predicted for higher values of the mass of the t¯t system and of the top-quark transverse momentum. Lastly, the measurements can also discriminate among different sets of parton distribution functions.