A measurement of the proton structure function F₂ at low x at the HERA collider

The work presented in this thesis has been done in the H1 experiment at the HERA electron-proton collider. Its goal was to measure the proton structure function F₂ in the full kinematical x-Q² plane which could be reached with the 1993 year's luminosity, where Q² is the squared momentum transfer and x the momentum fraction of the proton carried by the parton. This document is divided in two parts, the first one describing a set of subjects linked to the general work of this experiment, and the second describing the analysis made for the F₂ measurement. In the first part, a brief overview of the different physics subjects which are studied at HERA is given before the H1 detector being described. A discussion on the organisation of the computer facilities is shown afterward, with the example of H1. Then, a study of the pile-up background and a method to reject it is presented. The second part of this document presents the structure functions theories and the method used to measure them. The selections used to reject the background are shown, and the resolution of the detector is studied. After this, the measurement of the structure function F₂ is described. This measurement confirms with a better precision the rise of the structure function at low x, which has been observed for the first time with the 1992 HERA data. However, when the F₂ behaviour is studied as a function of W, the invariant mass of the photon-proton system, one could see that the rise of F₂ with W is smaller at low Q². The values of the measured F₂ at high Q² are compatible with the predictions of the Quantum Chromodynamics, though this measurement is not very accurate with the 1993 luminosity. (author)