An incremental approach to unravel the neutrino mass hierarchy and CP violation with a long-baseline Superbeam for large $\theta_{13}$

TL;DR

This paper proposes an incremental long-baseline neutrino experiment with a giant liquid argon detector at Pyh"asalmi, showing it can determine neutrino mass hierarchy and CP violation for large heta_{13} values within a feasible timeframe.

Contribution

It details a staged experimental approach using a conventional beam and large detector to efficiently measure neutrino mass ordering and CP violation, especially for large heta_{13}.

Findings

Mass hierarchy can be determined at 3 sigma with 10-20 kt detector in a few years.

3 sigma sensitivity to CP violation achievable if heta_{13} is sufficiently large.

Performance improves with increased exposure, enabling staged milestones for physics goals.

Abstract

Recent data from long-baseline neutrino oscillation experiments have provided new information on \theta_{13}, hinting that 0.01\lesssim sin^2 2\theta_{13} \lesssim 0.1 at 2 sigma C.L. Confirmation of this result with high significance will have a crucial impact on the optimization of the future long-baseline oscillation experiments designed to probe the neutrino mass ordering and leptonic CP violation. In this context, we expound in detail the physics reach of an experimental setup where neutrinos produced in a conventional wide-band beam facility at CERN are observed in a proposed Giant Liquid Argon detector at the Pyh\"asalmi mine, at a distance of 2290 km. This particular setup would have unprecedented sensitivity to the mass ordering and CP violation in the light of large \theta_{13}. With a 10 to 20 kt `pilot' detector and just a few years of neutrino beam running, the mass hierarchy could be determined, irrespective of the true values of \delta_{CP} and the mass hierarchy, at 3 sigma (5 sigma) C.L. if sin^2 2\theta_{13}(true) = 0.05 (0.1). With the same exposure, we start to have 3 sigma sensitivity to CP violation if sin^2 2\theta_{13}(true) > 0.05, in particular testing maximally CP-violating scenarios at a high C.L. After optimizing the neutrino and anti-neutrino running fractions, we study the performance of the setup as a function of the exposure, identifying three milestones to have roughly 30%, 50% and 70% coverage in \delta_{CP}(true) for 3 sigma CP violation discovery. For comparison, we also study the CERN to Slanic baseline of 1540 km. This work demonstrates that an incremental program, staged in terms of the exposure, can achieve the desired physics goals within a realistically feasible timescale, and produce significant new results at each stage.