Beta-Beams: present design and expected

Abstract. We give the present status of the beta-beam study, which aims at producing intense ν e and νe beams from the decay of relativistic radioactive ions. The emphasis is put on recent technical progress and new ideas. The expected performances in terms of neutrino mixing parameters (θ 13 and CP violating phase δ) using a megaton water Cerenkov detector installed in the Fréjus underground laboratory are shown to be excellent, and the synergy with a a companion SuperBeam is underlined. 1. MOTIVATIONS Super-Kamiokande has given strong evidence for a maximal oscillation between νµand ντ [1], and several projects with accelerators have been designed to check this result. The first results of the K2K experiment [2] confirm the oscillation, and future projects (MINOS in the USA, OPERA and ICARUS at Gran Sasso) should refine the oscillation parameters by 2010. More recently, after the results from SNO [3] and Kamland [4], a solid proof for solar neutrino flavour oscillations governed by the so-called LMA solution has been established. We can no longer escape the fact that neutrinos have indeed a mass, although the absolute scale is not yet known. Furthermore, the large mixing angles of the tw