First experience with colliding electron-proton beams in HERA

We report on first experience with colliding electron and proton beams in HERA. In 1992, the first year of operation, HERA has delivered some 60(nb)^-1 of e-p luminosity to the experiments H1 and ZEUS. The beam energies amounted to 26 GeV and 820 GeV. A maximum luminosity of 2.2×10²⁹ cm^-2 s^-1 has been achieved by colliding a train of nine electron bunches against nine proton bunches. A complete collection of data is contained in a reference. The beams could be brought into and held in collision without problems. The lifetime of the proton beam in collision is as long as 50h. This requires both careful matching of the electron and proton beam cross sections and also that the two orbits coincide within ≃0.2σ beam size at the interaction point. The proton beam suffered a beam-beam tune shift of up to ΔQ_x≃0.0018. This is close to the limit which was assumed in the design of HERA. Nonetheless, there is only little degradation in the proton beam quality in collision. Under these conditions, the proton beam fills could be stored and be made available for collision for some 24 h in HERA