Endpoint Logarithms in e+e- -> J/psi + eta_c

TL;DR

This paper analyzes the origin of double logarithms in the cross section of e+e- -> J/psi + eta_c at NLO, identifying Sudakov and endpoint contributions, and suggests a way to factorize and resum these logarithms.

Contribution

It provides a detailed diagram-by-diagram analysis of double logarithms and reinterprets endpoint logarithms in terms of soft spectator fermion regions, aiding all-orders factorization.

Findings

Sudakov double logarithms cancel out in total

Endpoint double logarithms persist and are linked to soft spectator lines

Reinterpretation may facilitate all-orders resummation of logarithms

Abstract

We investigate the origin of the double logarithms of Q^2/m_c^2 that appear in the calculation of the cross section for e+e- -> J/psi + eta_c at next-to-leading order in alpha_s. We find that, diagram-by-diagram, the double logarithms are accounted for by Sudakov double logarithms and endpoint double logarithms. The Sudakov double logarithms cancel in the sum over all diagrams, but the endpoint double logarithms do not. We reinterpret the endpoint double logarithms in terms of a leading region of loop integration in which a spectator fermion line becomes soft. This reinterpretation may simplify the process of establishing an all-orders factorization theorem for this helicity-flip process, which, in turn, might allow one to resum logarithms of Q^2/m_c^2 to all orders in alpha_s.