Atmospheric neutrinos in ice and measurement of neutrino oscillation parameters

A large number of experiments of different types have provided strong evidence for neutrino oscillations and thus for physics beyond the Standard Model (see Ref. [1] and references therein). Cosmic ray interactions in the atmosphere give a natural source of neutrinos. These atmospheric neutrinos in the GeV range have been used by the Super-Kamiokande (SK) detector to provide evidence for neutrino oscillations [2]. The large size of neutrino telescopes such as AMANDA, IceCube and KM3NeTmakes possible the detection of a large number of atmospheric neutrino events with a higher energy threshold, ∼ 100 GeV, even though the neutrino flux decreases rapidly with energy (∼ E ν ). These observatories were built to detect neutrinos from astrophysical sources, or from the annihilation of Weakly Interacting Massive Particles (WIMPs) [3]. Because of the high threshold energies, neutrino oscillation effects in these ice/water Cherenkov detectors are small. Recently, a low energy extension of the IceCube detector, the IceCube Deep Core array (ICDC) has been proposed and deployed [4]. It consists of six densely instrumented strings (7m spacing between optical modules) located in the deep center region of the IceCube detector plus the seven nearest standard IceCube strings. Its goal is to significantly improve the atmospheric muon rejection and to extend the IceCube neutrino detection capabilities in the low energy domain, down to muon or cascade energies as low as 5 GeV. The instrumented volume is 15 Mton. Such a low threshold array bubried deep inside IceCube will open up a new energy window on the universe. It will search for neutrinos from sources in the Southern hemisphere, in particular, from the galactic center region, as well as for neutrinos fromWIMP annihilation, as originally motivated. In [5] we have proposed neutrino oscillation physics as a further motivation for building such an array. In particular, we have analyzed the sensitivity of ICDC to the neutrino mass hierarchy. ICDC can detect tens of thousands of atmospheric neutrino events per year, orders of magnitude beyond the present data sample, providing rich opportunities for detailed oscillation studies. In [6] we have also analyzed the cascade signal in ICDC, showing that this can be used to get a high rate of ντ interactions. Here we concentrate on the muon neutrino disappearance analysis in ICDC, exploring the precision that can be reached in the measurement of the main neutrino oscillation parameters, ∆m231 and θ23. Section II reviews briefly our present knowledge of the neutrino oscillation parameters as well as their expected uncertainties from near future facilities. We then proceed in section III to describe the analysis presented here and the results obtained from it. We close with an outlook in section IV.