Dortmund

A measurement of the inclusive deep inelastic positron proton scattering cross-section at low momentum transfers squared Q 2 between 0.2 GeV 2 and 3.5 GeV 2 and values of Bjorken x down to 3 · 10 −5 is presented. Based on this the proton structure function F2, parameterising the quark composition of the proton, is extracted. Measurements at these low values of Q 2 are particularly interesting since perturbative calculations based on Quantum Chromodynamics, the theory of the strong interaction, can no longer be performed and only phenomenological models are able to describe the proton structure. Experimentally this transition region can be accessed by shifting the interaction point of positrons and protons into the direction of the incoming proton. This possibility has been exploited in the year 2000 during a special running period of the HERA collider. The present analysis is based on data recorded with the H1 detector at that time. Compared to a similar data taking period in 1995 the statistical error of the data sample is smaller by a factor of two. Due to a detailed investigation of the systematic uncertainties affecting the measurement it has been possible to reduce the total error by almost the same amount. The improved precision should allow for a better constraint of the available phenomenological models. Kurzfassun