Gain fractions of future neutrino oscillation facilities over T2K and NOvA

TL;DR

This paper assesses how future neutrino oscillation experiments' chances of discovering CP violation and mass hierarchy depend on early results from T2K and NOvA, highlighting the importance of continued running for optimal discovery potential.

Contribution

It provides a quantitative analysis of how early hints at T2K and NOvA influence the discovery probabilities of upcoming neutrino experiments, emphasizing the value of extended data collection.

Findings

If T2K and NOvA do not observe hints after 15 years, LBNE and T2HK have less than 10% chance of 5sigma CP violation discovery.

Early hints at T2K and NOvA significantly increase the likelihood of T2HK achieving 5sigma CP violation detection.

Hierarchy measurement at 5sigma is highly probable (>90%) at LBNE and NF10 regardless of T2K and NOvA results.

Abstract

We evaluate the probability of future neutrino oscillation facilities to discover leptonic CP violation and/or measure the neutrino mass hierarchy. We study how this probability is affected by positive or negative hints for these observables to be found at T2K and NOvA. We consider the following facilities: LBNE; T2HK; and the 10 GeV Neutrino Factory (NF10), and show how their discovery probabilities change with the running time of T2K and NOvA conditioned to their results. We find that, if after 15 years T2K and NOvA have not observed a 90% CL hint of CP violation, then LBNE and T2HK have less than a 10% chance of achieving a 5sigma discovery, whereas NF10 still has a ca 40% chance to do so. Conversely, if T2K and NOvA have an early 90% CL hint in 5 years from now, T2HK has a rather large chance to achieve a 5sigma CP violation discovery (75% or 55%, depending on whether the mass hierarchy is known or not). This is to be compared with the 90% (30%) probability that NF10 (LBNE) would have to observe the same signal at 5sigma. A hierarchy measurement at 5sigma is achievable at both LBNE and NF10 with more than 90% probability, irrespectively of the outcome of T2K and NOvA. We also find that if LBNE or a similar very long baseline super-beam is the only next generation facility to be built, then it is very useful to continue running T2K and NOvA (or at least T2K) beyond their original schedule in order to increase the CP violation discovery chances, given their complementarity.