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


Book Description

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 $\sqrt{s}$


Book Description

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.




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


Book Description

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.




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


Book Description

"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.




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


Book Description

The top quark pair production cross section is measured for the first time in proton-proton collisions at √s= 13 TeV by theCMS experiment at the CERN LHC, using data corresponding to an integrated luminosity of 42 pb-1. The measurement is performed by analyzing events with at least one electron and one muon of opposite charge, and at least two jets. We then measured the cross section and found that was 769 ± 60 (stat) ± 55 (syst) ± 92 (lumi) pb, in agreement with the expectation from the standard model.







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


Book Description

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)


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.