Direct measurement of the top-quark width with the ATLAS experiment

[摘要] In this thesis a measurement of the total decay width of the top quark, Г\(_{top}\) is presented using selected semi-leptonic \({t¯t}\) event candidates, recorded from protonproton collisions at a centre-of-mass energy of \(\sqrt{s}\) = 8 TeV with the ATLAS experiment at CERN in Geneva, Switzerland. The total recorded integrated luminosity that was used for this measurement equals to \(\int\)Ldt = 20.3 fb\(^{−1}\). The analysis includes the two event channels: \(e\) + jets and \(μ\) + jets. The reconstruction of the \({t¯t}\) system is achieved by using a per-event \(X\)2 minimisation technique. Official Monte Carlo samples have been used to simulate the t¯t signal and background contributions in order to perform simulated experiments to obtain the statistical and systematic uncertainties. The results obtained from the measurement of the top parameter are: Г\(_{top}\) = 1.65 GeV for the \(μ\) + jets channel and Г\(_{top}\) = 0.81 GeV for the \(e\) + jets channel. The upper limits obtained from the measured values and the analysis total uncertainties are: Г\(_{top}\) < 4.60 GeV at 68 % C.L. and Г\(_{top}\) < 7.16 GeV at 95 % C.L. for the \(μ\) + jets channel, and Г\(_{top}\) < 4.40 GeV at 68 % C.L. and Г\(_{top}\) < 7.51 GeV at 95 % C.L. for the \(e\) + jets channel. These results are consistent with the expected SM value Г\(_{top}\) ≈ 1.33 GeV.

[发布机构] University:University of Birmingham;Department:School of Physics and Astronomy

[关键词] Q Science;QC Physics