Abstract
The top-quark mass is a parameter of paramount importance in the Standard Model, playing a crucial role in the electroweak precision tests and in the stability of the Standard Model vacuum. I will discuss the main strategies to extract the top-quark mass at the LHC and the interpretation of the measurements in terms of well-posed top-mass definitions, taking particular care about renormalon ambiguities, Monte Carlo event generators and theoretical uncertainties.
Highlights
The mass of the top quark is a fundamental parameter of the Standard Model, since it enters in the electroweak precision tests [1] and constrained the mass of the Higgs boson even before its discovery at the LHC
The last couple of decades has seen a tremendous progress in the implementation of Monte Carlo event generators, besides the reknowned general-purpose HERWIG [31, 32] and PYTHIA [33, 34], in such a way that several reliable programs are currently available for the top-mass analyses
The total ttcross section was calculated in QCD in the NNLO+NNLL approximation in Czakon et al [74] 11 and was used to determine mt by ATLAS in Aad et al [75] (7 and 8 TeV data) and by CMS in Khachatryan et al [76]
Summary
The mass of the top quark is a fundamental parameter of the Standard Model, since it enters in the electroweak precision tests [1] and constrained the mass of the Higgs boson even before its discovery at the LHC. Possible changes of the central value or of the uncertainty on mt may affect the results in Degrassi et al [4], to the point of even moving the vacuum position inside the stability or instability regions It is of paramount importance determining mt at the LHC with the highest possible precision, estimating reliably all sources of uncertainty and eventually interpreting the results in terms of field-theory mass definitions. As will be discussed later, even the so-called pole or MS mass determinations are not completely Monte Carlo independent, since the evaluation of the experimental acceptance depends, though quite mildly, on the shower code which is employed and on the implemented mass parameter. The interpretation of the measurements and the theoretical uncertainties will be investigated in section 5, while section 6 will contain some final remarks
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