Measuring the Neutrino Mass Ordering with KM3NeT/ORCA and JUNO


Neutrino physics is one of the most exciting topics in contemporary physics, leading to two Nobel prizes in the last 20 years for the detection of cosmic neutrinos and the discovery that neutrinos have mass. The massive nature of neutrinos is arguably the strongest indication of physics beyond the Standard Model of particle physics, opening a number of fundamental questions: What is the mechanism for neutrino mass generation? Are neutrinos responsible of the matter-antimatter imbalance in the universe? Can neutrinos tell us something about the unification of fundamental forces? Do neutrinos feel the quantum nature of space-time? A new generation of neutrino experiments is in the horizon looking to explore many of these still open questions on neutrino properties and searching for astrophysical sources.

The main focus of this PhD thesis proposal will be the study of atmospheric neutrino oscillations with the KM3NeT/ORCA detector and its combination with the upcoming JUNO data. KM3NeT [1] is a multi-Megaton detector under construction in the Mediterranean Sea. The detectors consist of arrays of Photo-Multiplier Tubes (PMTs) submerged in the deepest regions of the Mediterranean, where few cosmic rays can reach and the clear seawater provides a huge natural target for neutrino interactions. The ORCA detector of KM3NeT is a densely instrumented configuration which will focus on observing atmospheric neutrinos to measure fundamental neutrino properties. ORCA is currently taking data with 17% of its planned instrumentation in place (19 Detector Units (DUs)), and construction is moving ahead quickly with ~30% expected to be deployed by the end of 2024 and the full detector is planned by 2028. With the detectors growing rapidly, ORCA has already started to perform its first measurement of the Neutrino Mass Ordering (NMO) showing a slight preference to the normal ordering at ~1 sigma [2]. JUNO is a large liquid scintillator detector under construction in China at a distance of 53km from a couple of nuclear power plants [3]. It will measure the oscillations of reactor electron anti-neutrinos with extreme precision, providing a completely independent measurement of the NMO. The detector is planned to come online in 2024 and is expected to reach 3 sigma sensitivity to the NMO in 6 years.

The NMO measurement can be significantly enhanced by the combination of ORCA and JUNO data as shown in a study led by a former PhD student in the APC group [4] in collaboration with colleagues from IPHC. This PhD proposal will capitalize from that initial effort to develop the first combined ORCA and JUNO NMO analyses with early data. The candidate will be a member of the KM3NeT collaboration and their primary work will consist in the NMO measurement in this context, as well as contributions to the energy calibration and reconstruction efforts. In the same time, they are expected to strengthen the links with the JUNO collaboration in order to combine the two analysis results. Within the timescale of the PhD, we expect the ORCA data alone to provide sensitivity to the NMO at 2-3 sigma level, and a combined measurement with JUNO may boost this sensitivity up to 4 sigma.

The KM3NeT group at APC is strongly involved in the analysis of neutrino oscillations with ORCA, as well as instrumentation activities on the Calibration Unit, characterization of the Digital Optical Modules, Machine Learning developments, and searching for astrophysical neutrinos with ORCA and ARCA. We are one of the largest groups in KM3NeT with high visibility in the collaboration, comprising 12 permanent physicists, 6 technical staff, 4 postdocs and 4 PhD students. The successful candidate will join our team measuring neutrino properties with ORCA. With the experiment already in data-taking mode, the candidate will be expected to take part in the many aspects of data processing, calibration and monitoring. The position is based at APC and will be co-supervised by Dr. Joao Coelho and Dr. Benjamin Trocmé. Frequent interaction with the KM3NeT Collaboration is expected, including regular meetings, and contributing to the installation, operation and maintenance of the detectors. Many of these interactions will require frequent travel to collaborating institutions and control centres, amounting to 3-4 times a year. Some experience with programming in C++ and/or Python, and particle physics data analysis would be highly appreciated. Whenever possible, we strongly encourage candidates to also join us in advance for a master's project on a similar project.


[1] KM3NeT Collaboration, Letter of Intent for KM3NeT Phase 2 J.Phys. G43(2016) no.8, 084001,
[2] V. Carretero [KM3NeT], Measuring atmospheric neutrino oscillation with KM3NeT/ORCA6, PoS ICRC2023 (2023), 996,
[3] JUNO Collaboration, JUNO physics and detector, Prog. Part. Nucl. Phys. 123 (2022), 103927,
[4] KM3NeT Collaboration, Combined sensitivity of JUNO and KM3NeT/ORCA to the neutrino mass ordering, JHEP 03 (2022), 055,


João Coelho, Benjamin Trocmé






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