Solving Degeneracies at a $\beta$-Beam by Combining Ions

Abstract

We study how the eightfold-degeneracy in the (${\theta }_{13},\delta$) plane observed in $\gamma \sim 100$ $\beta$-beams can be reduced by periodically changing the ions in the storage ring. This ``ions cocktail'' allows to change the neutrino energy, at fixed $\gamma$, by choosing ions with different decay energies. We propose to combine the standard ${}^6$He and ${}^{18}$Ne beams with ${}^8$Li and ${}^8$B ones. These latter two ions have peaked ${\nu }_e\to {\nu }_{\mu }$ oscillation probabilities for $\gamma =100$ at a baseline $L\sim 700$ Km. At this distance and this $\gamma$ the oscillation probability of ${}^6$He and ${}^{18}$Ne neutrinos is at its second maximum. This setup is particularly suited for large enough values of ${\theta }_{13}$ (within reach at T2K-I) and it allows solving most of the eightfold-degeneracy, measuring ${\theta }_{13},\delta$ and the sign of the atmospheric mass difference for values of ${\theta }_{13}\ge 5^{\circ }$.

Comments: Talk given at the XLIrst Rencontres de Moriond session devoted to Electroweak Interactions And Unified Theories in March 2006. 4 pages, 4 figures