29 research outputs found
Factorization and resummation for generic hierarchies between Jets
Jets are an important probe to identify the hard interaction of interest at
the LHC. They are routinely used in Standard Model precision measurements as
well as in searches for new heavy particles, including jet substructure
methods. In processes with several jets, one typically encounters hierarchies
in the jet transverse momenta and/or dijet invariant masses. Large logarithms
of the ratios of these kinematic jet scales in the cross section are at present
primarily described by parton showers. We present a general factorization
framework called SCET, which is an extension of Soft-Collinear Effective
Theory (SCET) and allows for a systematic higher-order resummation of such
kinematic logarithms for generic jet hierarchies. In SCET additional
intermediate soft/collinear modes are used to resolve jets arising from
additional soft and/or collinear QCD emissions. The resulting factorized cross
sections utilize collinear splitting amplitudes and soft gluon currents and
fully capture spin and color correlations. We discuss how to systematically
combine the different kinematic regimes to obtain a complete description of the
jet phase space. To present its application in a simple context, we use the
case of 3 jets. We then discuss in detail the application to N-jet
processes at hadron colliders, considering representative classes of
hierarchies from which the general case can be built. This includes in
particular multiple hierarchies that are either strongly ordered in angle or
energy or not.Comment: 63 pages, 6 figures, v2: minor typos fixed, Ref. added, v3: journal
versio
Soft functions for generic jet algorithms and observables at hadron colliders
We introduce a method to compute one-loop soft functions for exclusive N - jet processes at hadron colliders, allowing for different definitions of the algorithm that determines the jet regions and of the measurements in those regions. In particular, we generalize the N -jettiness hemisphere decomposition of ref. [1] in a manner that separates the dependence on the jet boundary from the observables measured inside the jet and beam regions. Results are given for several factorizable jet definitions, including anti-k T , XCone, and other geometric partitionings. We calculate explicitly the soft functions for angularity measurements, including jet mass and jet broadening, in pp → L + 1 jet and explore the differences for various jet vetoes and algorithms. This includes a consistent treatment of rapidity divergences when applicable. We also compute analytic results for these soft functions in an expansion for a small jet radius R. We find that the small-R results, including corrections up to O(R2), accurately capture the full behavior over a large range of R