== Short description of the tool ==
The aim is to build an event generator for quarkonium physics. Production rates are computed within the NRQCD theory (Non-Relativistic QCD, Bodwin, Braaten and Lepage, see hep-ph/9407339), where cross sections are expanded in %$\alpha_s$% and %$\normalsize v$%, the relative velocity in the heavy quarkonium state. As a result, cross sections read
where the creation of a heavy-quark pair is described by the short-distance coefficients %$\hat \sigma(Q\bar Q(n))$%, whereas the non-perturbative evolution of this heavy-quark pair into a quarkonium state is encoded into the long-distance matrix elements %$$%. The label %$\normalsize n $% stands for the intermediate state of the heavy quark pair, which is usually expressed in the spectroscopic notation:
with %$\normalsize S $% the spin of the heavy quark pair, %$ \normalsize L $% its orbital angular momentum, %$ \normalsize J $% its total angular momentum, and %$ \normalsize c $% its color state.
MadOnia automatically generates any tree-level amplitude for an arbitrary transition %$\normalsize n$% (up to P-wave state) required for the computation of the short-distance coefficients. The amplitude generator is interfaced with MadEvent to produce unweighted events. These events are written in the same format in the lhe format and can be passed through Pythia for the showering and hadronization.
-- Main.PierreArtoisenet - 02 Mar 2009