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Measurement of the Charge Asymmetry in Top-quark Pair Production in Proton-proton Collisions at Sqrt(s)

Measurement of the Charge Asymmetry in Top-quark Pair Production in Proton-proton Collisions at Sqrt(s)
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Total Pages:
Release: 2011
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The difference in angular distributions between top quarks and antiquarks, commonly referred to as the charge asymmetry, is measured in pp collisions at the LHC with the CMS experiment. The data sample corresponds to an integrated luminosity of 1.09 fb−1 at a centre-of-mass energy of 7 TeV. Top-quark pairs are selected in the final state with an electron or muon and four or more jets. At least one jet is identified as originating from b-quark hadronization. The charge asymmetry is measured in two variables, one based on the pseudorapidities ([eta]) of the top quarks and the other on their rapidities (y). The results A{sub C}{sup {eta}} = -0.017 ± 0.032(stat.){sub -0.036}{sup +0.025}(syst.) and A{sub C}{sup y} = -0.013 ± 0.028(stat.){sub -0.031}{sup +0.029}(syst.) are consistent within uncertainties with the standard-model predictions.


Measurement of the Charge Asymmetry in Top Quark Pair Production in Pp Collisions at $\sqrt{s}$

Measurement of the Charge Asymmetry in Top Quark Pair Production in Pp Collisions at $\sqrt{s}$
Author:
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Total Pages: 42
Release: 2015
Genre:
ISBN:

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The charge asymmetry in the production of top quark and antiquark pairs is measured in proton-proton collisions at a center-of-mass energy of 8 TeV. The data, corresponding to an integrated luminosity of 19.6 fb -1 were collected by the CMS experiment at the LHC. Events with a single isolated electron or muon, and four or more jets, at least one of which is likely to have originated from hadronization of a bottom quark, are selected. A template technique is used to measure the asymmetry in the distribution of differences in the top quark and antiquark absolute rapidities. The measured asymmetry is Ayc= [0.33_0.26 (stat)_0.33 (syst)]%, which is the most precise result to date. The results are compared to calculations based on the standard model and on several beyond-the-standard-model scenarios.


Measurement of Charge Asymmetry in Top Quark Pair Production at the Large Hadron Collider

Measurement of Charge Asymmetry in Top Quark Pair Production at the Large Hadron Collider
Author: Burton Andrew Betchart
Publisher:
Total Pages: 131
Release: 2013
Genre:
ISBN:

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"We present a measurement of charge asymmetry in the production of top and antitop quark pairs in proton-proton collisions, in a sample of 19:6 fb−1 of data collected by the CMS experiment at 8TeV center of mass energy in 2012. Selected events have a single isolated electron or muon, and at least four jets, at least one of which is likely due to a bottom quark. A template technique is employed to measure top-antitop asymmetry in two kinematic observables simultaneously, which allows attribution of contributions to the observed forward-central asymmetry from distinct Standard Model production mechanisms. An asymmetry Ayc = (0:15 ± 0:42)% is measured in the difference of absolute rapidities of top-antitop pairs, of which (0:00 ± 0:43)% is attributable to quark-antiquark initial states, and (0:18 ± 0:15)% is attributable to quark-gluon initial states. The first measurement of the transverse top quark charge asymmetry is also presented, with the result A[phi]c = (0:44 ± 0:50)%. Measurements of the inclusive asymmetry on selections with high and low top system mass and absolute rapidity are consistent with the main result. The results are compared to Standard Model predictions and measurements from the LHC and the Tevatron"--Page vii.


Top Quark Pair Production

Top Quark Pair Production
Author: Anna Christine Henrichs
Publisher: Springer Science & Business Media
Total Pages: 231
Release: 2013-10-04
Genre: Science
ISBN: 3319014870

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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.


Inclusive and Differential Measurements of the $\mathrm{ T \bar{t} }$ Charge Asymmetry in Pp Collisions at $\sqrt{s}

Inclusive and Differential Measurements of the $\mathrm{ T \bar{t} }$ Charge Asymmetry in Pp Collisions at $\sqrt{s}
Author:
Publisher:
Total Pages: 36
Release: 2015
Genre:
ISBN:

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The tt charge asymmetry is measured in proton-proton collisions at a centre-of-mass energy of 8 TeV. The data, collected with the CMS experiment at the LHC, correspond to an integrated luminosity of 19.7 fb-1 . Selected events contain an electron or a muon and four or more jets, where at least one jet is identified as originating from b-quark hadronization. The inclusive charge asymmetry is found to be 0.0010 " 0.0068 (stat) " 0.0037 (syst). In addition, differential charge asymmetries as a function of rapidity, transverse momentum, and invariant mass of the tt system are studied. For the first time at the LHC, our measurements are also performed in a reduced fiducial phase space of top quark pair production, with an integrated result of -0.0035 " 0.0072 (stat) " 0.0031 (syst). Additionally, all measurements are consistent within two standard deviations with zero asymmetry as well as with the predictions of the standard model.


First Measurement of the Cross Section for Top-Quark Pair Production in Proton-Proton Collisions at $\sqrt{s}

First Measurement of the Cross Section for Top-Quark Pair Production in Proton-Proton Collisions at $\sqrt{s}
Author:
Publisher:
Total Pages: 26
Release: 2011
Genre:
ISBN:

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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.


Measurement of the Top Quark Pair Production Cross Section in Pp Collisions at Sqrt(s)

Measurement of the Top Quark Pair Production Cross Section in Pp Collisions at Sqrt(s)
Author:
Publisher:
Total Pages: 31
Release: 2012
Genre:
ISBN:

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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.