Luminosity optimisation using beam-beam deflections at LEP

In maximizing the performance of the LEP electron-positron collider it is important to ensure that the beams collide head-on at the interaction points. The deflection of the beams due to the beam-beam interactions has been measured using orbit monitors located close to the interaction points. The dependence of the beam-beam deflection on the transverse distance between the beams has been used to optimise the overlap of the beams in the vertical plane and to measure the beam sizes at the interaction points.