QED Contribution to the Color-Singlet $\jpsi$ Production in $Υ$ Decay Near the Endpoint

Abstract

A recent study indicates that the $α^2α_s^2$ order QED processes of $Υ\to \jpsi + X$ decay are compatible with those of QCD processes. However, in the endpoint region, the Non-relativistic QED (NRQED) calculation breaks down since the collinear degrees of freedom are missing under the framework of this effective theory. In this paper we apply the soft collinear effective theory (SCET) to study the color-singlet QED process at the kinematic limit. Within this approach we are able to sum the kinematic logarithms by running operators using the renormalization group equations of SCET, which will lead to a dramatic change in the momentum distribution near the endpoint and the spectrum shape consistent with the experimental results.