LEP3: A high luminosity e+e- collider in the LHC tunnel to study the Higgs boson

Recent indications from the LHC suggest that the Higgs boson might be light, within the mass range 115- 130 GeV. Such object could be studied at an e+e− collider with about 240-GeV centre-of-mass energy. A corresponding Higgs factory – ‘LEP3’ – could be installed in the LHC tunnel, reducing its cost and also allowing for a second life of the two LHC general-purpose detectors. We present preliminary accelerator and beam parameters for LEP3 [1] tailored so as to provide a peak luminosity of 1034 cm-2s-1 at each of two experiments, while respecting a number of constraints including beamstrahlung limits. At this luminosity around 20,000 Higgs events per year per experiment could be obtained for a Standard Model Higgs boson with a mass of 115-130 GeV. For the parameters considered the estimated luminosity lifetime is about 16 minutes, and the synchrotron radiation losses are 50 MW per beam. High operational efficiency requires two rings: a low emittance collider storage ring operating at constant energy, and a separate accelerator to top up the colliding beams every few minutes. The alternative of a larger ring collider installed in a new, bigger tunnel will also be discussed. The LEP3 collider could as well operate on the Z resonance, where it would achieve luminosities above 1035 cm-2s-1.