Recent theoretical and experimental results on top quark mass measurements

Abstract

The top quark mass is a key parameter of the Standard Model of particle physics. Indeed it is one of the free parameters of the theory that needs to be measured to fully define it. The top quark mass is also an input of many precision predictions of the Standard Model that are needed to assess its validity up to higher energy scales, possibly up to the Planck scale. The great importance of the top quark mass for Standard Model and Beyond the Standard Model physics is motivation for the large efforts that the experimental community has put in its measurement. Remarkably, the LHC and TeVatron experiments have recently combined their results and obtained a combined measurement 173.34 ± 0.27(stat) ± 0.71(syst) GeV [1]. The uncertainty is dominated by systematic errors, in particular the measurement of hadornic jets, and is likely to not improve much when more data will be added to the analyses. The dominance of systematic errors in the current measurement is certainly a great motivation to think about new methods to mesure the top quark mass. At the end of Run-2 of the LHC it is foreseen to have few 1/ab of integrated luminosity, which would yield some 1 billion top pairs produced at the LHC. The prospect to have such large sample of top quarks makes possible to consider measurement of the top quark mass that exploit very special final states (such as for instance J/ψ states or other exclusive decays) or exploit features of kinematic distributions that are not hugely populated (such as for instance end-point regions and tails). The hope is that among these alternative approaches to the top quark mass measurement one can find methods that are based on experimentally clean quantities and that exploit observables which are well under theoretical control. The balance of these two needs will be a key issue for the methods that will provide a reliable precision determination of the top quark mass. The measurement of top quark mass through the measurement of the total inclusive pp→ tt cross-section is one instance of theoretically clean quantity, as it can be computed to high order in QCD, but, unfortunately, suffers of large uncertainties on the experimental side. The issue here has to do with the fact that the experiments measure the cross-section in the region of phase space accessible to their acceptance, not the total cross-section. The total cross-section