Structure Functions, the Gluon Density, and PQCD Tests

Measurements of the proton structure function F2 for 0:11 < Q 2 < 20000 GeV 2 and 1:2 10 5 < x < 0:65 from ZEUS 1994-1997 measurements are presented. From ZEUS 1994 and 1995 F2 data the slopes dF2=d lnQ 2 at xed x and d ln F2=d ln(1=x) for x < 0:01 at xed Q 2 are derived. For the latter E665 data are also used. The transition region in Q2 is explored using the simplest non-perturbative models and NLO QCD. The data at very low Q2 0:65GeV 2 are described successfully by Regge theory. From a NLO QCD t to ZEUS data the gluon density in the proton is extracted in the range 3 10 5 < x < 0:7. Data from NMC and BCDMS constrain the t at large x. Assuming the NLO QCD description to be valid down to Q2 1GeV 2, it is found that the q q sea distribution is still rising at small x and the lowest Q values whereas the gluon distribution is strongly suppressed. Preliminary ZEUS 1996-1997 F2 measurements are also presented.