Low x physics, deep inelastic scattering and structure functions

HERA experiments together with polarised fixed target lepton-nucleon scattering experiments and hadron-hadron interactions have provided this year a wealth of new results on the structure of the proton and on low x physics where x is the fraction of nucleon momentum carried by the struck quark in lepton a scattering. Measurement o the W charge asymmetry in CDF at FNAL has provided new constraints on the d/u ratio in the proton. The Drell-Yan asymmetry (σpp - σpn)/(σpp + σpn) measured by the NA51 experiment at CERN confirms that there are more of anti d than anti u in the proton. New data on proton, deuteron and neutron polarized structure functions from the SLAC E143 and CERN SMC experiments are in good agreement. The naive Ellis-Jaffe sum rule is violated by at least two standard deviations and the Bjorken Sum rule is verified to within about 10%. The measured QCD corrections to the Bjorken Sum Rule using the low Q2 data from E143 provide a new method to determine the QCD running coupling constant α5. Combining fixed target data from E665 and FNAL and HERA results from H1 and ZEUS, the measurements of the proton structure function F2(x,Q2) cover the very large kinematic range of 0.3 < Q2 < 104 GeV2 and 2.10-4 < x < 1. The steep rise of the structure function F2 with x decreasing is observed at x values below 10-1 and up to Q2 values of about 1000 GeV2. The interpretation of the F2 behaviour at low x by the BFKL and GLAP mechanisms is discussed together with possible ''footprints'' of the BFKL dynamics in the hadronic final states of deep inelastic scattering events at HERA. The properties of the deep inelastic scattering events at HERA with no energy in a large gap of rapidity close to the proton direction are reviewed. A signal from rapidity gap events in CDF and DO experiments is presented. (author). 102 refs., 31 figs., 5 tabs