Resummed event-shape variables in DIS
Mrinal Dasgupta, Gavin P. Salam
TL;DR
This paper completes the resummation program for DIS event shapes by delivering next-to-leading-log accuracy results for current-hemisphere observables (T_tE, rho_E, C_E) and by clarifying how these observables relate to the jet-mass framework familiar from e+e- annihilation. It introduces and treats non-global and discontinuously global logarithms, providing a factorized resummed expression with a non-global single-log factor and including PDF-dependent constant terms. The study also addresses practical issues such as speeding fixed-order Monte Carlo calculations and modeling non-perturbative $1/Q$ effects through a universal infrared coupling, enabling data-driven extractions of alpha_s and tests of universality. Finally, comparisons to HERA data across observables enable simultaneous fits of alpha_s and the nonperturbative parameter alpha_0, testing universality and refining our understanding of hadronization in DIS.
Abstract
We complete our study of resummed event-shape distributions in DIS by presenting results for the class of observables that includes the current jet mass, the C-parameter and the thrust with respect to the current-hemisphere thrust axis. We then compare our results to data for all observables for which data exist, fitting for alpha_s and testing the universality of non-perturbative 1/Q effects. A number of technical issues arise, including the extension of the concept of non-globalness to the case of discontinuous globalness; singularities and non-convergence of distributions other than in the Born limit; methods to speed up fixed-order Monte Carlo programs by up to an order of magnitude, relevant when dealing with many x and Q points; and the estimation of uncertainties on the predictions.