Seminari di gruppo IV

All-orders behaviour and renormalons in top-mass observables

by Paolo Nason (MIB)

1G09 (Dipartimento di Fisica, M. S. Angelo)


Dipartimento di Fisica, M. S. Angelo

The abundant production of top pairs at the LHC has provided an opportunity for accurate top mass measurements. The quoted errors of the LHC experimental collaborations have reached values near 500MeV, an accuracy of about three parts in a thousand. In spite of this, there are several theoretical issues, mostly related to non-perturbative effects that may affect the measurement at the level of some typical hadronic scales, i.e. are dangerously close to the present errors. In this talk I briefly review these issue, and present a study of non-perturbative corrections in a simplified context, the so called large-b0 approximation of QCD. This context is well defined and fully calculable, so that it can be used to address some debated questions, like: which mass scheme is more appropriate, whether (and in which mass scheme) leptonic observables have intrinsically less uncertainties, and whether (and in which mass scheme) the total cross section is free of non-perturbative uncertainties, and whether the mass of a reconstructed top should be interpreted as the pole or the MSbar mass.