p p solar neutrinos at DARWIN

The DARWIN collaboration recently argued that DARWIN (dark matter wimp search with liquid xenon) can collect, via neutrino-electron scattering, a large, useful sample of solar p p -neutrinos, and measure their survival probability with subpercent precision. We explore the physics potential of such a sample in more detail. We estimate that, with 300 ton-years of data, DARWIN can also measure, with the help of current solar neutrino data, the value of sin²θ₁₃ , with the potential to exclude sin²θ₁₃=0 close to the three-sigma level. We explore in some detail how well DARWIN can constrain the existence of a new neutrino mass-eigenstate ν₄ that is quasimass-degenerate with ν₁ and find that DARWIN's sensitivity supersedes that of all current and near-future searches for new, very light neutrinos. In particular, DARWIN can test the hypothesis that ν₁ is a pseudo-Dirac fermion as long as the induced mass-squared difference is larger than 10^-13 eV² , one order of magnitude more sensitive than existing constraints. Throughout, we allowed for the hypotheses that DARWIN is filled with natural xenon or ¹³⁶Xe -depleted xenon.