- Cabrera, Anatael;
- Han, Yang;
- Obolensky, Michel;
- Cavalier, Fabien;
- Coelho, João;
- Nicolás, Diana Navas;
- Nunokawa, Hiroshi;
- Simard, Laurent;
- Bian, Jianming;
- Nayak, Nitish;
- Ochoa-Ricoux, Juan Pedro;
- Roskovec, Bedřich;
- Chimenti, Pietro;
- Dusini, Stefano;
- Bongrand, Mathieu;
- Karaparambil, Rebin;
- Lebrin, Victor;
- Viaud, Benoit;
- Yermia, Frederic;
- Asquith, Lily;
- Bezerra, Thiago JC;
- Hartnell, Jeff;
- Lasorak, Pierre;
- Ling, Jiajie;
- Liao, Jiajun;
- Yu, Hongzhao
The measurement of neutrino Mass Ordering (MO) is a fundamental element for
the understanding of leptonic flavour sector of the Standard Model of Particle
Physics. Its determination relies on the precise measurement of $\Delta
m^2_{31}$ and $\Delta m^2_{32}$ using either neutrino vacuum oscillations, such
as the ones studied by medium baseline reactor experiments, or matter effect
modified oscillations such as those manifesting in long-baseline neutrino beams
(LB$\nu$B) or atmospheric neutrino experiments. Despite existing MO indication
today, a fully resolved MO measurement ($\geq$5$\sigma$) is most likely to
await for the next generation of neutrino experiments: JUNO, whose stand-alone
sensitivity is $\sim$3$\sigma$, or LB$\nu$B experiments (DUNE and
Hyper-Kamiokande). Upcoming atmospheric neutrino experiments are also expected
to provide precious information. In this work, we study the possible context
for the earliest full MO resolution. A firm resolution is possible even before
2028, exploiting mainly vacuum oscillation, upon the combination of JUNO and
the current generation of LB$\nu$B experiments (NOvA and T2K). This opportunity
is possible thanks to a powerful synergy boosting the overall sensitivity where
the sub-percent precision of $\Delta m^2_{32}$ by LB$\nu$B experiments is found
to be the leading order term for the MO earliest discovery. We also found that
the comparison between matter and vacuum driven oscillation results enables
unique discovery potential for physics beyond the Standard Model.