Iain Stewart (MIT) “Transverse Momentum Distributions: Infrared Connections between Euclidean and Minkowski Correlators”

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In this talk I will discuss the transverse momentum distribution of partons inside a proton, which are encoded by transverse-momentum dependent parton distribution functions (TMDPDFs). These TMDPDFs are important for predicting LHC cross sections, like the momentum spectrum for Higgs bosons or Drell-Yan, and also provide a means to probe the nature of confinement. The field theory definition of TMDPDFs involve a number of interesting features that are not present for the more well known longitudinal parton distributions. This includes the presence of additional vacuum matrix elements of Wilson lines, which encode final state interactions. At small transverse momentum qT, the TMDPDFs are genuinely nonperturbative objects. TMDPDFs depend on the hadron momentum, and have an associated evolution that is determined by a ‚Äúrapidity” anomalous dimension. For small qT this anomalous dimension must also be determined nonperturbatively, and is responsible for important contributions. By developing relations between the infrared physics of Euclidean and Minkowski correlators I will discuss a method for calculating this anomalous dimension using Lattice QCD.