ZEUS results on the measurement and phenomenology of F-2 at low x and low Q(2)

Measurements of the proton structure function F(2) for 0.6 < Q(2) < 17 GeV(2) and 1.2 x 10(-5) < x < 1.9 x 10(-3) from ZEUS 1995 shifted vertex data are presented. From ZEUS F(2) data the slopes dF(2)/dln Q(2) at fixed x and dlnF(2)/dln(1/x) for x < 0.01 at fixed Q(2) are derived. For the latter, E665 data are also used. The transition region in Q(2) is explored using the simplest non-perturbative models and NLO QCD. The data at very low Q(2) less than or equal to 0.65 GeV(2) are described successfully by a combination of generalised vector meson dominance and Regge theory. From a NLO QCD fit to ZEUS data the gluon density in the proton is extracted in the range 3 x 10(-5) < x < 0.7. Data from NMC and BCDMS constrain the fit at large x. Assuming the NLO QCD description to be valid down to Q(2) similar to 1 GeV(2), it is found that the q (q) over bar sea distribution is still rising at small x and the lowest Q(2) values whereas the gluon distribution is strongly suppressed.