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| Author | : Philipp Sturm |
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| Total Pages | : 0 |
| Release | : 2012 |
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| Author | : Philipp Sturm |
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| Total Pages | : 167 |
| Release | : 2012 |
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| Total Pages | : 43 |
| Release | : 2014 |
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Measurements are presented of the t-channel single-top-quark production cross section in proton-proton collisions at √s = 8 TeV. The results are based on a data sample corresponding to an integrated luminosity of 19.7 fb−1 recorded with the CMS detector at the LHC. The cross section is measured inclusively, as well as separately for top (t) and antitop $ \left(\overline{\mathrm{t}}\right) $, in final states with a muon or an electron. The measured inclusive t-channel cross section is?t-ch. = 83.6 ± 2.3 (stat.) ± 7.4 (syst.) pb. The single t and $ \overline{\mathrm{t}} $ cross sections are measured to be?t-ch.(t) = 53.8 ± 1.5 (stat.) ± 4.4 (syst.) pb and?$_{t-ch.}$ $ \left(\overline{t}\right) $ = 27.6 ± 1.3 (stat.) ± 3.7 (syst.) pb, respectively. The measured ratio of cross sections is Rt-ch. =?t-ch.(t)/?t-ch. $ \left(\overline{\mathrm{t}}\right) $ = 1.95 ± 0.10 (stat.) ± 0.19 (syst.), in agreement with the standard model prediction. The modulus of the Cabibbo-Kobayashi-Maskawa matrix element Vtb is extracted and, in combination with a previous CMS result at √s = 7 TeV, a value.
| Author | : Anna Christine Henrichs |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 231 |
| Release | : 2013-10-04 |
| Genre | : Science |
| ISBN | : 3319014870 |
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 | : Phillipp Tepel |
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| Release | : 2018 |
| Genre | : Fermions |
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| Total Pages | : 7 |
| Release | : 2009 |
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The D0 collaboration reports direct evidence for electroweak production of single top quarks through the t-channel exchange of a virtual W boson. This is the first analysis to isolate an individual single top quark production channel. We select events containing an isolated electron or muon, missing transverse energy, and two, three or four jets from 2.3 fb−1 of p{bar p} collisions at the Fermilab Tevatron Collider. One or two of the jets are identified as containing a b hadron. We combine three multivariate techniques optimized for the t-channel process to measure the t- and s-channel cross sections simultaneously. We measure cross sections of 3.14{sub -0.80}{sup +0.94} pb for the t-channel and 1.05 ± 0.81 pb for the s-channel. The measured t-channel result is found to have a significance of 4.8 standard deviations and is consistent with the standard model prediction.
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| Release | : 2011 |
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Electroweak production of the top quark is measured in pp collisions at sqrt(s) = 7 TeV, using a dataset collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 36 inverse picobarns. With an event selection optimized for t-channel production, two complementary analyses are performed. The first one exploits the special angular properties of the signal, together with background estimates from data. The second approach uses a multivariate analysis technique to probe the compatibility with signal topology expected from electroweak top quark production. The combined measurement of the cross section is 83.6 +/- 29.8 (stat.+syst.) +/- 3.3 (lumi.) pb, consistent with the standard model expectation.
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| Release | : 2016 |
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The cross section for the production of single top quarks in the $t$ channel is measured in proton-proton collisions at 13 TeV with the CMS detector at the LHC. The analyzed data correspond to an integrated luminosity of 2.3 fb$^{-1}$. The event selection requires one muon and two jets where one of the jets is identified as originating from a bottom quark. Several kinematic variables are then combined into a multivariate discriminator to distinguish signal from background events. A fit to the distribution of the discriminating variable yields a total cross section of 232 $\pm$ 13 (stat) $\pm$ 28 (syst) pb and a ratio of top quark and top antiquark production of $R_{t\textrm{-ch.}}= $ 1.81 $\pm$ 0.18 (stat) $\pm$ 0.15 (syst). From the total cross section the absolute value of the CKM matrix element $V_{\mathrm{tb}}$ is calculated to be 1.03 $\pm$ 0.07 (exp) $\pm$ 0.02 (theo). All results are in agreement with the standard model predictions.
| Author | : Mohammad Assadsolimani |
| Publisher | : disserta Verlag |
| Total Pages | : 161 |
| Release | : 2014-08 |
| Genre | : Science |
| ISBN | : 3954256746 |
It is known that the LHC has a considerable discovery potential because of its large centre-of-mass energy (vs =14 TeV) and the high design luminosity. In addition, the two experiments ATLAS and CMS perform precision measurements for numerous models in physics. The increasing experimental precision demands an even higher level of accuracy on the theoretical side. For a more precise prediction of outcomes, one has to consider the corrections obtained typically from Quantum Chromodynamics (QCD). The calculation of these corrections in the high energy regime is described by perturbation theory. In the present study, multi-loop calculations in QCD, including in particular two-loop corrections for single top quark production, are considered. There are several phenomenological motivations to study single top quark production: Firstly, the process is sensitive to the electroweak Wtb-vertex; moreover, non-standard couplings can hint at physics beyond the Standard Model. Secondly, the t-channel cross section measurement provides information on the b-quark Parton Distribution Functions (PDF). Finally, single top quark production enables us to directly measure the Cabibbo-Kobayashi-Maskawa(CKM) matrix element Vtb. The next-to-next-to-leading-order (NNLO) calculation of the single top quark production has many building blocks. In this study, two blocks will be presented: one-loop corrections squared and two-loop corrections interfered with Born. Initially, the one-loop squared contribution at NNLO for single top quark production will be calculated. Before we begin with the calculation of the two-loop corrections to single top quark production, we calculate the QCD form factors of heavy quarks at NNLO, along with the axial vector coupling as a first independent check. A comparison with the relevant literature suggests that this approach is in line with generally accepted procedure. This consistency check provides a proof of the validity of our setup. In the next step, the two-loop corrections to single top quark production will be calculated. After reducing all occurring tensor integrals to scalar integrals, we apply the integration by parts method (IBP) to find the master integrals. This step is a major challenge compared to all similar calculations because of the number of variables in the problem (two Mandelstam variables s and t, the dimension d and the mass of the top quark mt as well as the mass of the W boson mw). Finally, the calculation of the three kinds of topologies – vertex corrections, double boxes and non-planar double boxes – in the two-loop contribution at NNLO calculation will be presented.
| Author | : Pienpen Seema-Mergelmeyer |
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| Release | : 2018 |
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