874 research outputs found

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

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    In this thesis a measurement of the total decay width of the top quark, Гtop_{top} is presented using selected semi-leptonic tÂŻt{tÂŻt} event candidates, recorded from protonproton collisions at a centre-of-mass energy of s\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 ∫\intLdt = 20.3 fb−1^{−1}. The analysis includes the two event channels: ee + jets and ΌΌ + jets. The reconstruction of the tÂŻt{tÂŻt} system is achieved by using a per-event XX2 minimisation technique. Official Monte Carlo samples have been used to simulate the tÂŻt 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: Гtop_{top} = 1.65 GeV for the ΌΌ + jets channel and Гtop_{top} = 0.81 GeV for the ee + jets channel. The upper limits obtained from the measured values and the analysis total uncertainties are: Гtop_{top} < 4.60 GeV at 68 % C.L. and Гtop_{top} < 7.16 GeV at 95 % C.L. for the ΌΌ + jets channel, and Гtop_{top} < 4.40 GeV at 68 % C.L. and Гtop_{top} < 7.51 GeV at 95 % C.L. for the ee + jets channel. These results are consistent with the expected SM value Гtop_{top} ≈ 1.33 GeV

    An embedding technique to determine ττ backgrounds in proton-proton collision data

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    An embedding technique is presented to estimate standard model tau tau backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed mu mu events and replaced with simulated tau leptons with the same kinematic properties. In this way, a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed. The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at root s = 13 TeV corresponding to an integrated luminosity of 41.5 fb(-1).Peer reviewe

    Measurement of t(t)over-bar normalised multi-differential cross sections in pp collisions at root s=13 TeV, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions