Optimizing the greenfield Beta-beam

Abstract

We perform a comprehensive and detailed comparison of the physics reach of Beta-beam neutrino experiments between two pairs of plausible source ions, (⁸B, ⁸Li) and (¹⁸Ne, ⁶He). We study the optimal choices for the baseline, boost factor, and luminosity. We take a 50 kton iron calorimeter, a la ICAL@INO, as the far detector. We follow two complementary approaches for our study: (i) Fixing the number of useful ion decays and boost factor of the beam, and optimizing for the sensitivity reach between the two pairs of ions as a function of the baseline. (ii) Matching the shape of the spectrum between the two pairs of ions, and studying the requirements for baseline, boost factor, and luminosity. We find that for each pair of ions there are two baselines with very good sensitivity reaches: a short baseline with L [km]/γ≃2.6 (⁸B+⁸Li) and L [km]/γ≃0.8 (¹⁸Ne+⁶He), and a long "magic" baseline. For γ ~500, one would optimally use ¹⁸Ne and ⁶He at the short baseline for CP violation, ⁸B and ⁸Li at the magic baseline for the mass hierarchy, and either ¹⁸Ne and ⁶He at the short baseline or ⁸B and ⁸Li at the magic baseline for the sin²2θ₁₃discovery.