The Sudakov radiator for jet observables and the soft physical coupling

• Published in: The journal of high energy physics Vol. 2019; no. 1; pp. 1 - 40
• Main Authors: Banfi, Andrea, El-Menoufi, Basem Kamal, Monni, Pier Francesco
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.01.2019; Springer Nature B.V; SpringerOpen
• Subjects: Classical and Quantum Gravitation; Coupling; Elementary Particles; Emitters; High energy physics; Perturbative QCD; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quantum Physics; Radiators; Regular Article - Theoretical Physics; Relativity Theory; Resummation; String Theory; Resummation; Perturbative QCD
• ISSN: 1029-8479; 1029-8479
• DOI: 10.1007/JHEP01(2019)083

A bstract We present a procedure to calculate the Sudakov radiator for a generic recursive infrared and collinear (rIRC) safe observable whose distribution is characterised by two widely separated momentum scales. We give closed formulae for the radiator at next-to-next-to-leading-logarithmic (NNLL) accuracy, which completes the general NNLL resummation for this class of observables in the ARES method for processes with two emitters at the Born level. As a byproduct, we define a physical coupling in the soft limit, and we provide an explicit expression for its relation to the M S ¯ coupling up to O α s 3 . This physical coupling constitutes one of the ingredients for a NNLL accurate parton shower algorithm. As an application we obtain analytic NNLL results, of which several are new, for all angularities τ x defined with respect to both the thrust axis and the winner-take-all axis, and for the moments of energy-energy correlation FC x in e + e − annihilation. For the latter observables we find that, for some values of x , an accurate prediction of the peak of the differential distribution requires a simultaneous resummation of the logarithmic terms originating from the two-jet limit and at the Sudakov shoulder.