JUNO (physics experiment)

JUNO (physics experiment)
Name	JUNO
Location	Jiaolong Mountain
Established	2014
Participants	[]

JUNO (physics experiment) is a large-scale neutrino observatory located in southern China, designed to measure neutrino oscillation parameters, determine the neutrino mass ordering, and study a broad range of neutrino sources. The experiment deploys a 20-kilotonne liquid scintillator detector deep underground to reduce backgrounds from cosmic rays, aiming for unprecedented energy resolution and large statistical power to probe fundamental questions in particle and nuclear physics. JUNO is sited near nuclear reactors and integrates international expertise from institutions across Europe, Asia, and North America.

Overview

JUNO was proposed in the 2000s and approved by Chinese funding agencies and international partners to exploit the flux of electron antineutrinos from the nearby Yangjiang Nuclear Power Station and Taishan Nuclear Power Station. The central experimental strategy builds on concepts from the KamLAND experiment, the Daya Bay Reactor Neutrino Experiment, and the SNO detector, combining large mass with high photodetector coverage derived from developments in Super-Kamiokande and Borexino. JUNO’s underground site in Jiaolong Mountain provides overburden comparable to facilities like Gran Sasso Laboratory and Kamioka Observatory to suppress cosmic muon backgrounds and cosmogenic isotopes.

Detector Design and Components

The JUNO detector comprises a 35.4-meter-diameter acrylic sphere containing 20 kilotonnes of linear alkylbenzene-based liquid scintillator, surrounded by a water Cherenkov veto and a top tracker. The inner sphere is instrumented with about 17,612 20-inch photomultiplier tubes (PMTs) supplemented by ~25,000 3-inch PMTs to achieve both high photon collection and dynamic range, technologies influenced by developments at Hamamatsu, ET Enterprises, and Micro Channel Plate R&D groups. The water pool is lined with large-area PMTs and functions as a muon veto and passive shield, inspired by instrumentation at IceCube and ANTARES. Calibration systems include radioactive sources, LED light sources, and a remotely operated vehicle, echoing techniques used at Borexino and SNO+ to control systematic uncertainties in energy scale, nonlinearity, and position-dependent light collection.

Scientific Goals and Physics Program

JUNO’s primary physics objective is to determine the neutrino mass ordering (hierarchy) by measuring interference patterns in reactor antineutrino oscillations at a baseline of ~53 km, leveraging precision constraints on the solar and atmospheric oscillation parameters established by Super-Kamiokande, T2K, and NOvA. JUNO aims for sub-percent precision on sin^2(theta_12), Delta m^2_21, and Delta m^2_31, providing inputs critical to global fits used by the Particle Data Group and theoretical frameworks like the PMNS matrix. Secondary goals include studies of supernova neutrinos in coordination with the Supernova Early Warning System, geoneutrinos to probe radiogenic heat in the Earth, sterile neutrino searches in conjunction with results from LSND and MiniBooNE, and searches for proton decay channels complementary to Hyper-Kamiokande. JUNO also offers sensitivity to solar neutrinos, diffuse supernova background neutrinos, and exotic physics including neutrino magnetic moments and non-standard interactions explored in global analyses.

Construction and Commissioning

Construction began with civil works for the experimental hall in the mid-2010s, following engineering precedents from the Gran Sasso Laboratory expansions and the excavation techniques used at Jinping Underground Laboratory. The acrylic sphere fabrication and photomultiplier installation required collaboration among industrial partners and university laboratories, with logistics coordinated through national agencies such as the Chinese Academy of Sciences and partner institutions like CERN and national laboratories across France, Italy, Germany, United States, and Japan. Commissioning phases include detector filling, calibration runs, and progressive integration of PMT readout electronics, mirroring commissioning workflows from Daya Bay and KamLAND to validate energy resolution, timing synchronization, and background rejection prior to physics data-taking.

Data Acquisition and Analysis Methods

JUNO’s data acquisition system employs custom front-end electronics and waveform digitizers to record PMT signals with nanosecond timing precision, building on designs from BaBar and LHCb readout architectures for high-throughput streaming. Trigger algorithms distinguish inverse beta decay signatures from correlated backgrounds using prompt-delayed coincidence techniques pioneered at KamLAND and Daya Bay. Event reconstruction uses Monte Carlo simulations tuned with calibration datasets, adopting software frameworks interoperable with tools developed at ROOT and analysis standards from collaborations such as IceCube and NOvA. Systematic uncertainty control involves optical model calibration, energy nonlinearity corrections, and muon veto strategies comparable to those implemented at Borexino and Super-Kamiokande.

Collaboration and Organization

The JUNO collaboration comprises hundreds of scientists from universities, national laboratories, and research institutes across China, Italy, France, Germany, United Kingdom, United States, Spain, Switzerland, Russia, Japan, South Korea, and others, organized into working groups for detector hardware, software, physics analysis, and outreach. Governance follows a model similar to large experiments like ATLAS and CMS with spokespersons, an institutional board, and technical coordinators; funding and in-kind contributions are managed through memoranda of understanding with participating institutions and funding agencies such as the National Natural Science Foundation of China and European national research councils.

Results and Future Prospects

Early commissioning and calibration results have targeted demonstration of the design energy resolution goal and background rejection capabilities; upcoming physics runs are expected to deliver high-precision measurements that will impact global neutrino oscillation fits and constraints on theoretical models including leptonic CP violation when combined with accelerator experiments like DUNE and T2K. JUNO’s sensitivity to supernova and geoneutrinos positions it as a multi-messenger observatory within networks including the Super-Kamiokande and IceCube collaborations. Planned upgrades and long-term operation may expand searches for rare processes and strengthen synergies with next-generation facilities such as Hyper-Kamiokande and DUNE.

Category:Neutrino experiments