PS02 Rare Decays
An analysis of the inclusive Υ (1S) → η ′ X decay and constraints on the η ′-meson distribution amplitudes
Theory Division, CERN, CH-1211 Geneva 23, Switzerland
2 Institut für Theoretische Physik, Universität Bern, CH-3012 Bern, Switzerland
Accepted: 4 November 2003
Published online: 6 November 2003
We calculate the η ′-meson energy spectrum in the Υ (1S) → η ′ g g g → η ′ X decay in the leading-order perturbative QCD in the static-quark limit for the orthoquarkonium. Our principal result is the extraction of parameters of the η ′ g * g effective vertex function (EVF) involving a virtual and a real gluon from the available data on the hard part of the η ′-meson energy spectrum. The perturbative-QCD based framework provides a good description of the available CLEO data, allowing one to constrain the lowest Gegenbauer coefficients B (q) 2 and B (g) 2 of the quark-antiquark and gluonic distribution amplitudes of the η ′-meson. The resulting constraints are combined with the existing ones on these coefficients from an analysis of the η ′ – γ transition form factor and the requirement of positivity of the EVF, yielding B (q) 2 (μ 0 2) = –0.008 ± 0.054 and B (g) 2 (μ 0 2) = 4.6 ± 2.5 for μ 0 2 = 2 GeV2. This reduces significantly the current uncertainty on these coefficients.
© Società Italiana di Fisica, Springer-Verlag, 2004