Leading power SCET analysis of $e^{+}{e}^{-}\to J/\psi gg$

Abstract

Recently, Belle and BaBar Collaborations observed surprising suppression in the endpoint $J/\psi$ spectrum, which stimulates us to examine the endpoint behaviors of the $e^{+}{e}^{-}\to J/\psi gg$ production. We calculate the $J/\psi$ momentum and angular distributions for this process within the framework of the soft-collinear effective theory (SCET). The decreasing spectrum in the endpoint region is obtained by summing the Sudakov logarithms. We also find a large discrepancy between the NRQCD and SCET spectrum in the endpoint region even before the large logarithms are summed, which is probably due to the fact that only the scalar structure of the two-gluon system is picked out in the leading power expansion. A comparison with the process ${\rm Y}\to \gamma gg$ is made.

Comments: 12 pages, 3 figures, one reference added and some minor changes, version to appear in Phys. Lett. B