U2 - 5017 (Universita` Milano Bicocca)
Speakers: Jürg Andreas Haag (Universität Bern)
In this talk, I introduce a general framework for describing multijet cross sections in the limit where all radiation is either confined to n narrow jets or is soft. This n-jet limit is imposed by requiring a chosen n-jet resolution variable to lie below a small cutoff. In this regime, the cross section develops large double logarithms of the cut that must be resummed for reliable predictions. Using direct QCD methods and the method of regions, we derive a factorization theorem valid for a broad class of such resolution variables. It separates the cross section into hard, collinear, and soft functions, enabling systematic resummation and allowing the logarithmic structure at fixed order to be predicted. I will present a numerical calculation of the quark jet function for kt-like observables entering this factorization formula. As a first application, we compute the leading-power contribution to the Durham y23 cumulant at NNLO. Combined with the MATRIX framework, this result enables a slicing calculation of dijet production in lepton collisions at NNLO. The method achieves excellent numerical stability, demonstrating the feasibility of slicing with kt-type variables for jet processes.