A Second Detector Focusing on the Second Oscillation Maximum at an Off-axis Location to Enhance the Mass Hierarchy Discovery Potential in LBNE10

The Long Baseline Neutrino Oscillation Experiment (LBNE) is proposed to determine the neutrino mass hierarchy and measure the CP phase δCP in the leptonic sector. The current design of LBNE Phase I consists of a 10 kt liquid argon time projection chamber (LBNE10). The neutrino-antineutrino asymmetry in the electron-neutrino appearance probability has contributions from both the CP phase and the matter effect. For this reason, experimental sensitivity to the mass hierarchy depends both on the true value of the CP phase and the true mass hierarchy; LBNE10 will determine the mass hierarchy at high levels of significance for half of δCP phase space. We propose placing a second detector at an off-axis location. Such a detector will share the same beamline as the primary LBNE detector. The detector location is chosen such that this detector focuses on a measurement of electron (anti)neutrino appearance at the second oscillation maximum. We will show that this configuration will enhance the ability of LBNE to determine the mass hierarchy and to discover CP violation in the leptonic sector. The recent discovery of sizable θ13 with reactor electron anti-neutrino disappearance measurements [1, 2, 3, 4] and electron (anti-)neutrino appearance measurements [5, 6] opens door to the determination of the neutrino mass hierarchy (MH) and the CP phase δCP in the leptonic sector [7]. The neutrino mass hierarchy problem is to determine whether the third generation of neutrino is heavier (normal hierarchy/NH) or lighter (inverted hierarchy/IH) than the first two generations of neutrinos. Together with the next generation neutrinoless double beta decay experiments, the determination of the neutrino mass hierarchy may hold the key to the nature of neutrinos (Dirac or Majorana particles). A value of the CP phase not equal to zero or π may produce the CP-violation that is required for leptogenesis [8], which is a potential explanation for the apparent matter-anti-matter asymmetry in the universe. The determination of MH and the CP phase δCP will have profound significance not only within the neutrino physics, but in the larger field of high-energy physics. The Long-Baseline Neutrino Experiment (LBNE) [9] is designed to determine the MH and δCP simultaneously. By placing an on-axis detector at a baseline of 1300 km, LBNE will measure the (anti-)νμ to (anti-)νe oscillation. As shown in Fig. 1, the νμ to νe oscillation probabilities are (GeV) ν E 0 2 4 6 8 10 12 e ν → μ ν P