2 Neutral and Charged Current Dis at Large Q

Data from the HERA collider experiments, H1 and ZEUS, have been fundamental to the rapid recent development of our understanding of the partonic composition of the proton and of QCD. This report focuses on inclusive measurements of neutral and charged current cross sections at HERA, using the full available data taken to date. The present precision on the proton parton densities and the further requirements for future measurements at the Teva-tron and LHC are explored. Emphasis is also placed on the region of very low Bjorken-x and Q 2. In this region, the 'confinement' transition takes place from partons to hadrons as the relevant degrees of freedom and novel or exotic QCD effects associated with large parton densities are most likely to be observed. Finally, prospects for the second phase of HERA running are discussed. The presence of a point-like probe together with only one initial state hadron makes deep inelastic lepton nucleon scattering (DIS) the ideal environment in which to study the quantum chromodynam-ics (QCD) of hadronic interactions and to constrain the parton densities of the proton. In the years 1992-2000, the HERA collider experiments, H1 and ZEUS, collected ep data at electron beam energies of 27.5 GeV and proton energies of 820 GeV and 920 GeV, corresponding to ep center-of-mass energies in excess of 300 GeV. The data were split between around 100 pb −1 of e + p collisions and 15 pb −1 of e − p collisions. With the extensions in accessible kinematic phase space afforded by the large center-of-mass energy and the precise electron and hadron reconstruction in the experiments over a wide rapid-ity range, these data have been used to gain new insights into many aspects of ep collisions. This article focuses mainly on measurements of inclusive ep cross sections in both neutral current (NC, ep → eX) and charged current (CC, ep → νX) reactions throughout the available phase space. In most cases, the full available data from the first phase of HERA running are used. At relatively large momentum transfers, the inclusive cross sections yield important information on the parton densities of the proton. At small momentum transfers, they can be used to search for novel effects in quantum chromo-dynamics (QCD) associated with the large parton densities observed at the previously unexplored low momentum fractions of the struck quark. Less inclusive measurements concentrating on other aspects of ep scattering are described elsewhere …