  Regge theory provides a very simple and economical description of data for
(i) the proton structure function with x<0.07 and all available Q^2 values,
(ii) the charm structure function, and (iii) gamma p --> J/psi p. The data are
all in agreement with the assumption that there is a second pomeron, with
intercept about 1.4 . They suggest also that the contribution from the soft
pomeron is higher twist.
  This means that there is an urgent need to make perturbative evolution
compatible with Regge theory at small and not-so-small x, and to reassess the
magnitude of higher-twist contributions at quite small x.

High Energy Physics - Phenomenology;High Energy Physics - Experiment