Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665786
Title: Direct measurement of the top-quark width with the ATLAS experiment
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.