To get an idea of the spatial dimensions of (and charge distribution
inside) strictly neutral hadrons,
one has to extend the above considerations from elastic to transition
form factors. Their 
-slope at 
, known as the slope
parameter 
, is defined through
Quite frequently, it is expressed in terms of a parameter
, having
mass-dimensions and verifying 
. The
slope parameter
has essentially the same meaning
as in the previous case of charge radii, apart from the factor of 6 in
the definition.
Slope parameters for the 
transition form factors, with 
and 
, have been measured (
in the 
range or, equivalently, 
in the 
range) indicating that their dimensions are quite
compatible (once one accounts for the factor of 6) with those
previously discussed for their SU(3)-partners. In both cases, one
measures the spatial region where the electromagnetically active
hadron constituents can be found. In the first, charge-radius case one
has to deal with electrostatic or Coulombic interactions, while, in the
later 
transitions, magnetic interactions are
involved with quark-spin flipping and 
annihilations.