QCD corrections to radiative Υ decays

Abstract

We have calculated the next-to-leading order perturbative QCD corrections to the photon energy spectrum in radiative Υ decays. The higher-order corrections significantly modify the shape of the spectrum, in particular at large photon energies, and thereby reduce the discrepancy between experimental data and previous leading-order predictions. The next-to-leading order calculation of the photon energy spectrum allows a more reliable determination of the strong coupling constant from radiative Υ decays by restricting the analysis to the region of the energy spectrum that can be described by NLO perturbation theory.

Effective-field theories for heavy quarkonium

“…The review is not exhaustive. For instance, we shall not discuss one of the major phenomenological successes of NRQCD: explaining the heavy-quarkonium production rate at the Tevatron ͑Braaten et al, 1996;Beneke, 1997;Krämer, 2001;Bodwin et al, 2003͒. Before moving to the main body of the review, we list here our main notational choices ͑Yndurain, 1999͒. The QCD Lagrangian density reads…”

Extraction ofαsfrom radiativeΥ(1S)decays

“…where n f = 4 is the number of active flavors, α the fine structure constant, [16], [17,18], C ggg = 3.79 ± 0.54 (for n f = 4) [7,18], In order to obtain a sensible extraction, the ratios of NRQCD matrix elements R must be correctly estimated. R P 1 ( 3 S 1 ) can be related to the binding energy [19,20].…”

The dipole formalism for next-to-leading order QCD calculations with massive partons

“…If j is a gluon, then 24) where N F is the number of heavy flavours and N jk F is the number of those heavy flavours for which s jk > 4m F (m F + m k ). Note that for m F → 0, we can set N jk F = N F because the region of vanishing s jk gives a vanishing contribution to infrared-safe observables.…”

“…In recent years, it has been implemented in general purpose Monte Carlo codes for the calculation of 3-jet [10] and 4-jet observables [15,16] in e + e − annihilation, 2-jet [11,17] and 3-jet [17] final states in deep inelastic lepton-hadron scattering, production of three jets [18], vector-boson pairs [19], vector boson plus massless bb [20] and colourless supersymmetric particles [21] at hadron colliders. It has also been applied to the computation of QCD corrections to specific processes, such as 4-fermion final states [22] and forward-backward asymmetries [23] at high-energy e + e − colliders and to radiative quarkonium decays [24].…”