An analysis of the inclusive Υ (1S) → η X decay and constraints on the η-meson distribution amplitudes

  • Ahmed Ali
  • Alexander Y. Parkhomenko
PS02 Rare Decays


We calculate the η-meson energy spectrum in the Υ (1S) → η g g gη 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 ηγ transition form factor and the requirement of positivity of the EVF, yielding B(q)2 (μ02) = –0.008 ± 0.054 and B(g)2 (μ02) = 4.6 ± 2.5 for μ02 = 2 GeV2. This reduces significantly the current uncertainty on these coefficients.


Form Factor Transition Form Good Description Distribution Amplitude Principal Result 
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Copyright information

© Springer-Verlag, Società Italiana di Fisica 2003

Authors and Affiliations

  • Ahmed Ali
    • 1
  • Alexander Y. Parkhomenko
    • 2
  1. 1.Theory Division, CERN, CH-1211 Geneva 23Switzerland
  2. 2.Institut für Theoretische Physik, Universität Bern, CH-3012 BernSwitzerland

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