-machines have been already used to obtain some information on
the 
and 
transition form factors
around the 
peaks, where the cross-section is large
and interference effects are of interest. Some results can be seen in
refs. [2] and [11] and play a central role in
identifying the precise quark content of the above vector-mesons.
However, the corresponding slope parameters are more accurately known
through the (virtual) gamma-gamma scattering processes in 
reactions. Indeed, the data coming from different teams are in nice
agreement and may be averaged to give (see ref. [16] for
details)
Asymptotically, one expects [5] 
and the
related Brodsky-Lepage interpolation formula [17] predicts
, not far from (20).
