Top quark production at ATLAS and CMS

A review of the main recent results on top quark production from the ATLAS and CMS experiments is presented. Results on both electroweak single top quark production and strong top pair production are presented.Comment: Proceedings of the "Rencontres de Moriond 2014", EW session, 15-22 March 2014, La Thuile, Aosta valley, Ital

Top quark measurements in the CMS experiment

Experimental results on top-quark physics obtained at the CMS experiment are reported based on the data recorded at centre-of-mass energy up to 13 TeV. Inclusive and differential cross sections for both top-quark pair and single top-quark production are presented, as well as measurements of top-quark properties in production and decay, and searches for anomalous couplings. The presented measurements test theoretical predictions, including recent perturbative QCD calculations, provide constraints of fundamental standard model parameters, and set limits on physics beyond the standard model.Comment: 8 pages, 3 figures. To be submitted to European Physical Journal Web of Conference

The bias of the unbiased estimator: a study of the iterative application of the BLUE method

The best linear unbiased estimator (BLUE) is a popular statistical method adopted to combine multiple measurements of the same observable taking into account individual uncertainties and their correlation. The method is unbiased by construction if the true uncertainties and their correlation are known, but it may exhibit a bias if uncertainty estimates are used in place of the true ones, in particular if those estimated uncertainties depend on measured values. This is the case for instance when contributions to the total uncertainty are known as relative uncertainties. In those cases, an iterative application of the BLUE method may reduce the bias of the combined measurement. The impact of the iterative approach compared to the standard BLUE application is studied for a wide range of possible values of uncertainties and their correlation in the case of the combination of two measurements.Comment: 23 pages, 14 figures, accepted for publication in Nucl. Instr. and Meth.

Including gaussian uncertainty on the background estimate for upper limit calculations using Poissonian sampling

A procedure to include the uncertainty on the background estimate for upper limit calculations using Poissonian sampling is presented for the case where a Gaussian assumption on the uncertainty can be made. Under that hypothesis an analytic expression of the likelihood is derived which can be written in terms of polynomials defined by recursion. This expression may lead to a significant speed up of computing applications that extract the upper limits using Toy Monte Carlo.Comment: 6 pages, 2 figures, accepted for publication in Nucl.Instrum.Meth.

Combination of measurements and the BLUE method

The most accurate method to combine measurement from different experiments is to build a combined likelihood function and use it to perform the desired inference. This is not always possible for various reasons, hence approximate methods are often convenient. Among those, the best linear unbiased estimator (BLUE) is the most popular, allowing to take into account individual uncertainties and their correlations. The method is unbiased by construction if the true uncertainties and their correlations are known, but it may exhibit a bias if uncertainty estimates are used in place of the true ones, in particular if those estimated uncertainties depend on measured values. In those cases, an iterative application of the BLUE method may reduce the bias of the combined measurement.Comment: 10 pages, 4 figures, proceedings of the XIIth Quark Confinement and Hadron Spectrum conference, 28/8-2/9 2016, Tessaloniki, Greec