Jiangmen Underground Neutrino Observatory (JUNO)

Jiangmen Underground Neutrino Observatory (JUNO)
Name	Jiangmen Underground Neutrino Observatory
Location	Jiangmen, Guangdong, China
Type	Particle physics experiment

Jiangmen Underground Neutrino Observatory (JUNO) is a large-scale underground particle physics experiment located near Jiangmen in Guangdong province, China. It is designed to study neutrino oscillations from nuclear reactor sources and natural backgrounds, addressing questions connected to the neutrino mass hierarchy and precision measurements of mixing parameters. The project brings together institutions from across China, Europe, North America, and Asia and connects to broader programs in high-energy physics, astroparticle physics, and nuclear physics.

Overview

JUNO is a multi-institutional detector sited underground near the Daya Bay Nuclear Power Plant corridor to intercept reactor antineutrino flux from multiple reactor complexes. The central apparatus is a large liquid scintillator sphere instrumented with thousands of photomultiplier tube sensors to convert optical photons into electronic signals for timing and energy reconstruction. JUNO's design emphasizes excellent energy resolution and low backgrounds to enable spectral measurements and studies of reactor, solar, geoneutrino, supernova, and atmospheric neutrinos. Its operation links to international efforts exemplified by experiments such as Super-Kamiokande, SNO, KamLAND, DUNE, and IceCube.

Scientific Goals and Objectives

Primary scientific objectives include resolution of the neutrino mass ordering (also called hierarchy) through precision measurement of oscillation patterns at baselines of ~53 km from reactor cores, and determination of the oscillation parameters θ12, Δm21^2, and Δm31^2 with sub-percent precision. JUNO seeks to measure reactor antineutrino spectra to confront anomalies reported by LSND, MiniBooNE, and reactor flux models associated with the Reactor Antineutrino Anomaly. Secondary goals cover detection of neutrinos from a Galactic core-collapse supernova, studies of solar neutrinos including those from the pp chain and Boron-8, observation of geoneutrinos tied to Earth science and mantle composition debates, and searches for exotic phenomena such as sterile neutrinos, neutrino magnetic moments, and non-standard interactions tested by comparisons with NOνA and T2K results.

Detector Design and Components

The detector comprises a 35.4 m diameter acrylic sphere containing 20,000 tonnes of linear alkylbenzene-based liquid scintillator, surrounded by a water Cherenkov veto and an overburden rock shielding. The inner target is instrumented with ~17,612 20-inch photomultiplier tubes and an array of 3-inch photomultipliers to extend dynamic range and timing. Calibration systems include radioactive source deployment, laser systems, and cosmic muon trackers adapted from techniques used in Borexino, SNO+, and Baksan Neutrino Observatory. Electronics subsystems draw on developments from BESIII, LHC experiments such as ATLAS and CMS, and precision timing approaches similar to those in CTA and LIGO photon detection. Background mitigation employs radiopure materials procurement processes informed by GERDA, EXO-200, and CUORE low-background experience.

Construction and Site

The underground experimental hall is excavated beneath a mountain near Jiangmen with overburden to suppress cosmic-ray muons, following site selection criteria comparable to those for Gran Sasso Laboratory and Kamioka Observatory. Civil engineering involved tunneling methods referenced in construction projects like the Three Gorges Dam auxiliary works and coordination with regional authorities including China National Nuclear Corporation stakeholders. Logistics and material delivery required international shipping and customs arrangements with partners from CERN, University of California, Imperial College London, Tsinghua University, Peking University, and national laboratories such as IHEP and Brookhaven National Laboratory.

Operations and Data Analysis

Operational strategy emphasizes continuous reactor-synchronized data taking with real-time monitoring of detector stability, energy scale, and trigger efficiency. Data acquisition and processing pipelines use frameworks inspired by ROOT, Gaudi, and distributed computing models analogous to Worldwide LHC Computing Grid and Open Science Grid. Reconstruction algorithms implement particle identification, vertex finding, and spectral unfolding derived from methods used at KamLAND and Double Chooz, while statistical inference leverages techniques from Feldman–Cousins intervals, Bayesian analyses common in Planck cosmology work, and global fits coordinated with groups like NuFIT. Systematic uncertainty control draws on calibration runs, reactor operation logs from China General Nuclear Power Group, and cross-calibration with other neutrino observatories.

Collaboration and Funding

JUNO is organized as an international collaboration of universities and laboratories including major institutions such as Institute of High Energy Physics (IHEP), Shanghai Jiao Tong University, University of California, Berkeley, Princeton University, Oxford University, Max Planck Society, CEA Saclay, and KEK. Funding sources combine national research agencies like the National Natural Science Foundation of China, European funding bodies including ERC-supported groups, and contributions from national laboratories such as Argonne National Laboratory and Lawrence Berkeley National Laboratory. Governance follows collaboration bylaws with working groups modeled on structures used by ATLAS and CMS collaborations.

Results and Impact

Projected outcomes include a definitive determination of the neutrino mass ordering and precision oscillation parameter measurements that will inform theoretical models in neutrino physics and constrain beyond-Standard-Model scenarios investigated at CERN and in neutrino-less double beta decay searches like KamLAND-Zen and CUORE. JUNO's geoneutrino results will influence debates in geophysics about radiogenic heat contribution in the Earth's mantle and core, and supernova neutrino sensitivity will complement multimessenger observations as performed for SN 1987A and future Galactic events coordinated with LIGO–Virgo and electromagnetic observatories. The experiment advances detector technologies relevant to dark matter searches, photon detection, and large-scale liquid handling demonstrated in projects such as Borexino and SNO+.

Category:Neutrino experiments