Measurement of the proton structure function F2 and of the total photon-proton cross section σγ*totp at very low Q2 and very low x

The proton structure function F-2 has been measured in the range 0.045 GeV2 < Q(2) < 0.65 GeV2 and 6(.)10(-7) < x < 1(.)10(-3) using 3.9 pb(-1) of ep --> eX reactions recorded with the ZEUS detector in 1997. The analysis is based on data from the Beam Pipe Calorimeter (BPC) and the Beam Pipe Tracker (BPT). Compared to our previous analysis, the BPT permits improved background suppression and better control of systematic uncertainties, allowing the extension of the kinematic region of the measurement towards lower Q(2) as well as higher and lower y. Significant improvements have also been achieved in the simulation of the hadronic final state via a mixture of samples of non-diffractive and diffractive Monte Carlo events, generated by the programs DJANGO and RAPGAP.