A potentially interesting case involves the 
reaction, where an elusive neutral scalar S (
or 
)
is produced. Its
observation could certainly contribute to solve the old controversy
concerning the nature or quark-content of these scalars. The
corresponding gauge invariant structure is easily found to be
For the VS transitions, not restricted now by the gauge invariance of the final photon, two form factors are possible, each one affecting independently one of the two terms in eq.(8).
The number of independent form factors increases when
higher spins are considered.
Three of them completely describe the 
production of
vector-meson pairs, 
, such as 
.
The situation is kinematically similar to that for the W gauge
bosons and suggests the association of the three form factors to the
electric charge, dipole magnetic moment and quadrupolar electric
moment distributions inside those vector-mesons.
