Seminario di Fenomenologia Dr. Johannes Michel (DESY, Hamburg)
Differential measurements at the LHC involve many physical scales set by the hard production process and soft or collinear QCD dynamics. When these scales are widely separated, the perturbative series becomes dominated by logarithms of their ratios. Precise (or sometimes even just physical) theory predictions require the resummation of these large logarithms to all orders. In this talk I will provide an overview of the challenges encountered when extending the resummation program to multi-differential observables, and of the new insights one gains into the infrared structure of QCD. I will first briefly review single-differential resummation methods, focusing on TMD factorization and the inclusive transverse momentum spectrum of electroweak gauge bosons at the LHC as a key application. I will then discuss how additional measurements on the decay products of the Z or W affect the resummation (e.g. fiducial acceptance cuts, the lepton pT, or the phi* observable), and present ongoing work to incorporate these effects at the level of precision required for determinations of key electroweak parameters such as the W mass at the LHC.
In the second half of the talk I will show how treating a very basic QCD quantity (the Drell-Yan rapidity spectrum) in a multi-differential spirit leads to surprising new insight into its all-order perturbative structure, and generalizes the classic QCD result of threshold (or soft-gluon) resummation.