Abstract
A review of the measurements of the tt̄ production cross section (inclusive and differential) performed by the CMS experiment at the LHC is given. The results are used to constrain the magnitude of most of the relevant systematics affecting precision measurements in the top quark sector. In addition from the determination of the top quark pair production cross section it is possible to determine the strong coupling constant as αS(mZ) = 0.1178+0.0046−0.0040 in agreement with the current world average. After the combination of several channels and techniques explored to measure the top quark mass in data, a precise determination of this quantity is made at CMS: mt = 173.4±0.4stat ± 0.9syst GeV. The measurement of the difference Δmt = mt − mt̄ is also presented.
Highlights
Amongst the quark family the top quark has revealed experimentally exceptional characteristics
The precise determination of the top quark properties is crucial to the success of understanding the Standard Model (SM) and its limitations in particular the origin of mechanism which originates EWK symmetry breaking
The experiments located at the Large Hadron Collider (LHC) have a unique opportunity to analyse this high statistics top quark sample and to study its properties with improved accuracy with respect to the Tevatron experiments
Summary
Amongst the quark family the top quark has revealed experimentally exceptional characteristics. In particular it is crucial to address how well does pQCD model the data and to identify its main dependencies and uncertainties related to the Q2 scale, ME-PS matching thresholds, hadronization and fragmentation effects These are crucial characterizations on the road to the search for new physics effects underlying the tt sample as well as to establish the ttH vertex where at least 4 jets are expected in the case H → bb. The so called jet gap fraction (fraction of events with no jet above a given pT threshold) is particular sensitive to these variations and it is shown, right It displays the preference for a higher Q2 value than the one used by the nominal simulation in CMS and the fact that the variations considered to evaluate the systematic uncertainties pertaining these parameters are in good agreement with what is observed in data. It is important to conclude referring that in these studies the uncertainties ranges usually from 3% at low multiplicities to 20% at high multiplicities and are dominated by jet energy scale and tt modelling parameters
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