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Register a new userInvestigation of top mass measurements with the ATLAS detector at LHC
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Several methods for the determination of the mass of the top quark with the ATLAS detector at the LHC are presented. All dominant decay channels of the top quark can be explored. The measurements are in most cases dominated by systematic uncertainties. New methods have been developed to control those related to the detector. The results indicate that a total error on the top mass at the level of 1 GeV should be achievable.
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A direct search for charged lepton-flavour violation in top-quark decays is presented. The data analysed correspond to $79.8 text{fb}^{-1}$ of proton--proton collisions at a centre-of-mass energy of $sqrt{s}=13 text{TeV}$ recorded by the ATLAS experiment at the LHC. The process studied is the production of top-quark pairs, where one top quark decays into a pair of opposite-sign different-flavour charged leptons and an up-type quark, while the other decays semileptonically according to the Standard Model. The signature of the signal is thus characterised by the presence of three charged leptons, a light jet and a $b$-jet. A multivariate discriminant is deployed and its distribution used as input to extract the signal strength. In the absence of a signal, an upper limit on the branching ratio of ${cal B}(t to ell ell q) < 1.86 times 10^{-5}$ is set at the 95% confidence level.
Recent measurements of top quark properties at the LHC made with the ATLAS and CMS experiments are discussed. The presented results include top quark mass, width, top quark Yukawa coupling, forward-backward and charge asymmetries, spin correlations and polarization, and W boson polarization. The results are compared to the standard model predictions and limits on new physics from these measurements are also presented.
An estimation of the sensitivity to measure Bs-Bsbar oscillations with the ATLAS detector is given for the detector geometry of initial layout. The delta ms reach is derived from unbinned maximum likelihood amplitude fits using Bs0 events generated with a simplified Monte Carlo method.
We present the latest measurements of the top quark mass from the Tevatron. The different top decay channels and measurement techniques used for these results are also described. The world average of the top quark mass based on some of these new results combined with previous results is mtop=172.6+-1.4 GeV.
Absolute luminosity measurements are of general interest for colliding-beam experiments at storage rings. These measurements are necessary to determine the absolute cross-sections of reaction processes and are valuable to quantify the performance of the accelerator. Using data taken in 2010, LHCb has applied two methods to determine the absolute scale of its luminosity measurements for proton-proton collisions at the LHC with a centre-of-mass energy of 7 TeV. In addition to the classic van der Meer scan method a novel technique has been developed which makes use of direct imaging of the individual beams using beam-gas and beam-beam interactions. This beam imaging method is made possible by the high resolution of the LHCb vertex detector and the close proximity of the detector to the beams, and allows beam parameters such as positions, angles and widths to be determined. The results of the two methods have comparable precision and are in good agreement. Combining the two methods, an overall precision of 3.5% in the absolute luminosity determination is reached. The techniques used to transport the absolute luminosity calibration to the full 2010 data-taking period are presented.
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