BEAMING NEUTRINOS AND ANTI-NEUTRINOS ACROSS THE EARTH TO DISENTANGLE NEUTRINO MIXING PARAMETERS

A result from MINOS seemed to indicate that the mass splitting and mixing angle of anti-neutrinos is different from that of neutrinos, suggesting a charge-parity-time (CPT) violation in the lepton sector. However, more recent MINOS data reduced the νμ–¯νμ differences leading to a narrow discrepancy nearly compatible with no CPT violation. However, the last few years of OPERA activity on the appearance of a tau lepton (one unique event) still has not been probed and more tools may be required to disentangle a list of parameters (μ–τ flavor mixing, tau appearance, any eventual CPT violation, θ13 angle value, and any hierarchy neutrino mass). Atmospheric anisotropy in muon neutrino spectra in the DeepCore, at ten to tens of GeV (unpublished), can hardly reveal asymmetry in the eventual νμ–¯νμ oscillation parameters. Here we considered how the longest baseline neutrino oscillation available, crossing most of Earth’s diameter, may improve the measurement and at best disentangle any hypothetical CPT violation occurring between the earliest (2010) and the present (2012) MINOS bounds (with 6σ a year), while testing τ and even the appearance of ¯ τ at the highest rate. The νμ and ¯νμ disappearance correlated with the tau appearance is considered for those events at the largest distances. We thus propose a beam of νμ and ¯νμ crossing through the Earth, within an OPERA-like experiment from CERN (or Fermilab), in the direction of the IceCube–DeepCore ν detector at the South Pole. The ideal energy lies at 21 GeV to test the disappearance or (for any tiny CPT violation) the partial ¯νμ appearance. Such a tuned detection experiment may lead to a strong signature of τ or ¯ τ generation even within its neutral current noise background events: nearly one ¯ τ or two τ a day. The tau appearance signal is above (or within) 10σ a year, even for a 1% OPERA-like experiment. Peculiar configurations for θ13 and the hierarchy neutrino mass test may also be better addressed by a DeepCore–PINGU array detector beaming νμ and observing νe at 6 GeV neutrino energy windows.