CP violation and mass hierarchy at medium baselines in the large theta(13) era

TL;DR

This paper explores how medium baseline neutrino experiments can effectively measure CP violation and determine the neutrino mass hierarchy in the context of a large theta(13) angle, emphasizing the importance of systematic control.

Contribution

It demonstrates that medium baseline superbeams are optimal for CP violation studies and can resolve the mass hierarchy with spectral information, especially with large theta(13).

Findings

Medium baselines remain optimal for CP violation measurement.

Spectral information helps resolve mass hierarchy at medium baselines.

Longer baselines with matter effects improve hierarchy sensitivity.

Abstract

The large value of theta(13) recently measured by rector and accelerator experiments opens unprecedented opportunities for precision oscillation physics. In this paper, we reconsider the physics reach of medium baseline superbeams. For theta(13) ~ 9 degree we show that facilities at medium baselines -- i.e. L ~ O(1000 km) -- remain optimal for the study of CP violation in the leptonic sector, although their ultimate precision strongly depends on experimental systematics. This is demonstrated in particular for facilities of practical interest in Europe: a CERN to Gran Sasso and CERN to Phyasalmi nu_mu beam based on the present SPS and on new high power 50 GeV proton driver. Due to the large value of theta(13), spectral information can be employed at medium baselines to resolve the sign ambiguity and determine the neutrino mass hierarchy. However, longer baselines, where matter effects dominate the nu_mu->nu_e transition, can achieve much stronger sensitivity to sign(Delta m^2) even at moderate exposures.