QCD Seminars

Dissecting the NNLL structure of collinear parton splittings

by Mrinal Dasgupta (University of Manchester (GB))

4/3-006 - TH Conference Room (CERN)

4/3-006 - TH Conference Room


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We explore the collinear limit of final-state quark splittings at order \alpha_s^2. While at NLL level this involves simple iteration of the standard 1 to 2 DGLAP splitting functions, at the NNLL level we need to consider triple-collinear splitting functions. By performing suitable integrals of the 1 to 3 splitting functions we demonstrate how to extract B2(z), a differential version of the coefficient B2 that  enters the quark form factor at NNLL and governs the intensity of collinear radiation from a quark. The variable z refers to the quark energy fraction after an initial 1 to 2 splitting and our results represent effective higher-order splitting functions and give one of the key analytical ingredients needed for the construction of NNLL parton showers. While in the limit z \to 1 we recover the standard soft limit results involving the CMW coupling with scale k_t, the z dependence we obtain motivates the extension of the concept of a physical coupling to beyond the soft limit.

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Elena Gianolio
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Alexander Yohei Huss, Samuel Abreu, Ben Page, Michelangelo Mangano, Pier Francesco Monni, Silvia Ferrario Ravasio, Pascal Pignereau
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