| This thesis presents a new method to measure the neutral current cross section up to Bjorken-x values equal to one. This method is employed to the data collected with the ZEUS detector at HERA using an integrated luminosity of 65.1 pb-1 for e +p collisions and of 16.7 pb-1 for e-p collisions at s = 318 GeV and 38.6 pb-1 for e +p at s = 300 GeV. Cross sections have been measured for Q 2 >= 648 GeV2 and are compared to predictions using different parton density functions. For the highest x bins, the data has a tendency to lie above the expectations using the recent PDF parametrizations. A preliminary QCD fit shows clear constraints on the form of the parton density functions at the highest values of x. |
