Sub-leading power corrections to transition form factors of η and η′ mesons from twist-six contributions

Abstract

Using collinear factorization, we have calculated twist-six corrections to ηγ and transition form factors in QCD. Only a subset of light-cone operators of twist-six, which can be factorized as a product of two gauge-invariant operators, have been considered assuming negligible contribution of non-factorizable operators. Corrections arising from finite meson mass and the finite s-quark mass have also been accounted for. The resulting power corrections start as 1/Q4-type of terms. While the twist-six contribution for the η meson is a couple of times smaller in magnitude than the twist-four contribution, for the η′ meson these two contributions turn out to be comparable. The matrix element of the pseudoscalar quark current for u- and d-quarks between the vacuum and one-meson state, hq, has considerable influence on the result. Expressions obtained by superimposing our results on those obtained in the literature for leading and sub-leading power corrections from lower twists have been plotted and compared with data.