Ionization cooled ultra pure beta-beams for long distance neu-e to neu-mu transitions, theta13 phase and CP-violation

Abstract

The key process is the observation of tiny oscillation mixing between numu and nue related to so far unknown theta13 amplitude, at distances corresponding to an invariant neutrino flight path around about 2.0 MeV/km. Zucchelli [12] has proposed the production of very pure neue beams (beta beams), in which relativistic radio-nuclides are stored in a high energy storage ring and decay in a long straight section pointing toward the neutrino detector far away. This method produces ultra pure anti-neue (He-6) and neue (Ne-18) with a negligible numu contamination (10-5). A novel kind of beta element production has been recently proposed [15] in which slow (v about 0.1 c) fully ionized ions are stored in a very small storage ring. Products like the isomeric doublet Li-7(d,p) Li-8 and Li-6(He3,n) B-8 are stopped in some foils few micron thick, from which they quickly diffuse as neutral atoms. The improvements are shown to be considerable. An ion source, a chain of several accelerators in cascade and a high energy storage/decay ring can produce a B-8 induced nue spectrum which has as much as 7.7 times higher energy than the one from He-6 induced anti-nue for a given magnetic rigidity of the storage ring. At a given neutrino energy, the CC cross sections for nue are about 3 times larger than the ones of anti-nue while the NC/CC inelastic pion background faking muons is about 3 times smaller. An optimal neu-e source might be fully ionized B-8 from the 120 GeV Main Energy Injector at FNAL, followed by a decay storage ring and a neutrino fly path of about 700-800 km. As detector we consider a LAr TPC with a fiducial mass of 50 to 100 kton. Such a technology should permit to detect a background free signal for sin2(2theta13) as small as about 6.0 x 10-4. By comparison, the present experimental limit is < 0.14.