Jiangmen Underground Neutrino Observatory Detector Research Articles

JUNO high purity nitrogen plant

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kt low level radioactivity liquid scintillator detector in a laboratory 650 m underground. An excellent energy resolution and a large volume offer exciting opportunities for addressing many important topics in neutrino physics. High purity nitrogen is an important factor to ensure the low background of the JUNO detector. High Purity Nitrogen (HPN) is used for detector purging, pipe cleaning, and scintillator purification, among other things in JUNO. According to JUNO’s requirements, the radon concentration in HPN should be less than 10 μBq/m3. To meet this requirement, A high-purity nitrogen plant with 100 Nm3/h maximum rate was designed and constructed. Low-temperature adsorption technology is used to remove radioactive impurities in nitrogen. High purification efficiency was ensured by using an activated carbon column with high column height-to-diameter ratio. Electrostatic collection and low-temperature enrichment methods are combined to measure radon in nitrogen. After ten days of continuous operation at 50 Nm3/h flux rate, the plant can to reduce the radon concentration in nitrogen from 37.4±1.8μBq/m3 to less than 1.33 μBq/m3. After HPN with flow rate of 50 Nm3/h passing through low-background pipeline (About 1.3 km), the radon concentration of HPN is 5.6±0.6μBq/m3.

Simulation software of the JUNO experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose experiment, under construction in southeast China, that is designed to determine the neutrino mass ordering and precisely measure neutrino oscillation parameters. Monte Carlo simulation plays an important role for JUNO detector design, detector commissioning, offline data processing, and physics processing. The JUNO experiment has the world’s largest liquid scintillator detector instrumented with many thousands of PMTs. The broad energy range of interest, long lifetime, and the large scale present data processing challenges across all areas. This paper describes the JUNO simulation software, highlighting the challenges of JUNO simulation and solutions to meet these challenges, including such issues as support for time-correlated analysis, event mixing, event correlation and handling the simulation of many millions of optical photons.

Probing high-energy solar axion flux with a large scintillation neutrino detector

We investigate the 5.49 MeV solar axions flux produced in the $p(d,\, ^{3}{\rm He})a$ reaction and analyze the potential to detect it with the forthcoming large underground neutrino oscillation experiment Jiangmen Underground Neutrino Observatory (JUNO). The JUNO detector could reveal axions through various processes such as Compton and inverse Primakoff conversion, as well as through their decay into two photons or electron-positron pairs inside the detector. We perform a detailed numerical analysis in order to forecast the sensitivity on different combinations of the axion-electron ($ g_{ae} $), axion-photon ($g_{a\gamma}$), and isovector axion-nucleon ($ g_{3aN} $) couplings, using the expected JUNO data for different benchmark values of axion mass in a model-independent way. We find that JUNO would improve by approximately one order of magnitude current bounds by Borexino and it has the best sensitivity among neutrino experiments.

Influencing factors of time resolution for LPMT for JUNO

Large area PMTs (LPMT) are widely used in neutrino experiments and cosmic ray detection. To meet the performance requirements for Jiangmen Underground Neutrino Observatory (JUNO), researchers at IHEP developed 20-inch MCP-PMTs which provide higher collection efficiency at a lower cost. 15k 20-inch PMTs produced by North Night Vision Technology Co., Ltd. (NNVT) has been delivered to Jiangmen and are to be installed as the central liquid scintillator detector of JUNO. Compared with prototype, though the collection efficiency (CE) and the quantum efficiency (QE) of the 15k MCP-PMTs get improved, the time performance gets worse. In this manuscript, the reasons for the deterioration of time resolution of the 15k MCP-PMTs are explored from several aspects. The optimized structure with great TTS of less than 5 ns is also introduced.

JUNO Oscillation Physics

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kton multi-purpose liquid scintillator detector with an expected energy resolution, under construction in a 700 m underground laboratory in the south of China (Jiangmen city, Guangdong province). The exceptional energy resolution and the massive fiducial volume of the JUNO detector offer great opportunities for addressing many essential topics in neutrino and astroparticle physics. JUNO’s primary goals are to determine the neutrino mass ordering and precisely measure the related neutrino oscillation parameters. With six years of data taking with reactor antineutrinos, JUNO can determine the mass ordering at a 3-4σ significance and the neutrino oscillation parameters sin2 θ 12, , and to a precision of better than 0.6%. In addition, the atmospheric neutrino and solar neutrino measurement at JUNO can also provide complementary and important information for neutrino oscillation physics. This work focuses on the oscillation physics of JUNO, which includes measurement and analysis of the reactor neutrinos, the atmospheric neutrinos, and the solar neutrinos. With the delicate energy response calibration and event reconstruction potential, JUNO will make a world-leading measurement on the neutrino oscillation parameters and neutrino mass ordering in the near future.

Summary of the R&D of 20-inch MCP-PMTs for neutrino detection

The Jiangmen Underground Neutrino Observatory (JUNO) in China aiming to determine the neutrino mass hierarchy is under construction. A new kind of large area microchannel-plate photomultiplier tube (MCP-PMT) was put forward for the JUNO by the researchers in Institute of High Energy Physics (IHEP) in China. After breaking through several core technotical barriers, the 20-inch MCP-PMT prototype with great performance was successfully produced by the MCP-PMT group in China and got 75% PMT orders (15,000 pics) from JUNO. The mass production line and batch test system was completed in North Night Vision Technology Co., Ltd. (NNVT). The performance of the MCP-PMT including the gain, the quantum efficiency, the P/V ratio, the dark count rate and the transit time spread can be batch tested. During the mass production process, the technical progress in the cathode deposition method improved the quantum efficiency of the photocathode from 30% to 35%. The aging behaviour, temperature effect, the after-pulse distribution and the flash signal of the 20-inch MCP-PMT are all detailly studied. By August of 2020, the 15,000 MCP-PMTs, which will be installed as the central liquid scintillator detector of JUNO, have been completed and delivered to Jiangmen. The average QE at 400 nm for the 15,000 pieces of MCP-PMTs is 32%.

JUNO sensitivity to low energy atmospheric neutrino spectra

Atmospheric neutrinos are one of the most relevant natural neutrino sources that can be exploited to infer properties about cosmic rays and neutrino oscillations. The Jiangmen Underground Neutrino Observatory (JUNO) experiment, a 20 kton liquid scintillator detector with excellent energy resolution is currently under construction in China. JUNO will be able to detect several atmospheric neutrinos per day given the large volume. A study on the JUNO detection and reconstruction capabilities of atmospheric nu _e and nu _mu fluxes is presented in this paper. In this study, a sample of atmospheric neutrino Monte Carlo events has been generated, starting from theoretical models, and then processed by the detector simulation. The excellent timing resolution of the 3” PMT light detection system of JUNO detector and the much higher light yield for scintillation over Cherenkov allow to measure the time structure of the scintillation light with very high precision. Since nu _e and nu _mu interactions produce a slightly different light pattern, the different time evolution of light allows to discriminate the flavor of primary neutrinos. A probabilistic unfolding method has been used, in order to infer the primary neutrino energy spectrum from the detector experimental observables. The simulated spectrum has been reconstructed between 100 MeV and 10 GeV, showing a great potential of the detector in the atmospheric low energy region.

Muon reconstruction with a convolutional neural network in the JUNO detector

The Jiangmen Underground Neutrino Observatory (JUNO) is designed to determine the neutrino mass ordering and measure neutrino oscillation parameters. A precise muon reconstruction is crucial to reduce one of the major backgrounds induced by cosmic muons. This article proposes a novel muon reconstruction method based on convolutional neural network (CNN) models. In this method, the track information reconstructed by the top tracker is used for network training. The training dataset is augmented by applying a rotation to muon tracks to compensate for the limited angular coverage of the top tracker. The muon reconstruction with the CNN model can produce unbiased tracks with performance that spatial resolution is better than 10 cm and angular resolution is better than 0.6 degrees. By using a GPU accelerated implementation a speedup factor of 100 compared to existing CPU techniques has been demonstrated.

A practical approach of high precision U and Th concentration measurement in acrylic

The Jiangmen Underground Neutrino Observatory (JUNO) will build the world’s largest liquid scintillator detector to study neutrinos from various sources. The 20 kilo tonne (kton) liquid scintillator will be stored in a 0.6 kton acrylic sphere with 35.4 m diameter due to the good light transparency, chemical compatibility and low radioactivity of acrylic. The concentration of U/Th in acrylic is required to be less than 1 ppt (10−12 g/g) to achieve a low radioactive background in the fiducial volume of the JUNO detector. The mass production of acrylic has started, and the quality control requires a fast and reliable radioassay on U/Th in acrylic. We have developed a practical method of measuring U/Th in acrylic to sub-ppt level using the Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The U/Th in acrylic can be concentrated by vaporizing acrylic in a class 100 environment, and the residue will be collected and sent to ICP-MS for measuring U/Th. All the other chemical operation is done in a class 100 clean room, and the ICP-MS measurement is done in a class 1000 clean room. The recovery efficiency is studied by adding the natural nonexistent nuclei 229Th and 233U as the tracers. The resulting method detection limit with 99% confidence can reach 0.04/0.09 ppt 238U/232Th in acrylic with (77.5 ± 3.4)% and (73.6 ± 4.1)% recovery efficiency. This equipment and method can not only be used for the quality control of JUNO acrylic, but also be further optimized for the radioassay on other materials with extremely low radioactivity, such as ultra-pure water and liquid scintillator.

Neutral-current background induced by atmospheric neutrinos at large liquid-scintillator detectors. I. Model predictions

The experimental searches for diffuse supernova neutrino background and proton decay in next-generation large liquid-scintillator (LS) detectors are competitive with and complementary to those in the water-Cherenkov detectors. In this paper, we carry out a systematic study of the dominant background induced by atmospheric neutrinos via their neutral-current (NC) interactions with the $^{12}{\rm C}$ nuclei in the LS detectors. The atmospheric neutrino fluxes at the location of Jiangmen Underground Neutrino Observatory (JUNO) are used, as the JUNO detector is obviously a suitable representative for future LS detectors. Then, we implement the sophisticated generators \texttt{GENIE} and \texttt{NuWro} to simulate the neutrino interactions with the carbon nuclei, and the package \texttt{TALYS} to deal with the deexcitations of final-state nuclei. Finally, the event rates for the production of additional nucleons, $\gamma$'s, $\alpha$'s, pions and kaons are obtained and categorized, and the systematic uncertainty of the NC background represented by a variety of data-driven nuclear models is estimated. The implications of the NC background from atmospheric neutrinos for the detection of diffuse supernova neutrino background and proton decay are also discussed.

JUNO detector: design and construction

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20-kton multi-purpose liquid scintillator detector currently being built in a dedicated underground laboratory located in the Jiangmen province (Southern China). JUNO' s main physics goal is the determination of the neutrino mass ordering using electron anti-neutrinos from two nuclear power plants at a baseline of about 53 km. This crucial measurement is supported by an unprecedented energy resolution of 3% at 1 MeV . Furthermore, the detector could observe supernova neutrinos, study atmospheric, solar and geo-neutrinos and perform exotic searches. Several challenges have been overcome during the construction of the largest liquid scintillator detector in the world, such as compatibility of the sphere material, mechanics of the stainless steel structure, scintillator light yield and transparency, PMTs detection efficiency. In this talk, JUNO's design as well as the status of its construction will be presented, together with a short excursion into its rich R&D program.

Tested Performance of JUNO 20” PMTs

The physics goal of the Jiangmen Underground Neutrino Observatory (JUNO) is mainly to determine the neutrino mass hierarchy by precisely measuring the oscillation spectrum with energy resolution.Totally, about 20, 000 large area 20” tubes with high photon detection efficiency will be used to achieve this requirement, including 5,000 Hamamatsu dynode PMTs and 15,000 NNVT MCP PMTs. The JUNO collaboration has built two systems to check the performances of these tubes, which have been running since July 2017 and about 14000 tubes have been tested, so far. The key parameters compared with vendor data, including operating voltage, photon detection efficiency, dark count rate, rise time, fall time are presented. The selected PMTs meet all the requirements of the JUNO detector.

Thermal reliability analysis of the central detector of JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy, precisely measure oscillation parameters and study solar neutrinos, supernova neutrinos and geo-neutrinos, etc. The central detector (CD) of JUNO has 20,000 tons liquid scintillator as target mass, which contains inside a huge acrylic sphere with inner diameter of 35.4 m, supported by a stainless steel structure. The whole structure of CD will be installed inside a cylindrical water pool, and the acrylic sphere will be submerged in the center of water pool. The operating temperature of CD is designed to be 21 °C as long as over 20 years, which is determined by the mechanical requirement of the structure and physics consideration. For this operating temperature, a special cooling system will be used to maintain the temperature inside the water pool. The main structure of CD is composed of acrylic and stainless steel, and they have much different thermal expansion coefficients, strengths and life times. Change in temperature may affect the safety of CD. As part of reliability analysis, the effect of cooling system failure on the CD is considered, and finite element method is used in our thermal calculation. In this article, the temperature fields before and after cooling system failure are calculated and analyzed, and the temperatures of different locations of water pool after cooling system failure are compared and discussed in detail.

An SOA-Based Design of JUNO DAQ Online Software

The Online Software, manager of the Jiangmen Underground Neutrino Observatory (JUNO) data acquisition (DAQ) system, is composed of many distributed components working coordinately. It takes the responsibility of configuring, processes management, controlling, and information sharing. The design of service-oriented architecture (SOA) makes the Online Software lightweight, loosely coupled, reusable, modular, self-contained, and easy to be extended. All the services in the SOA distributed Online Software system will send messages to each other without an intermediate broker. Hence, the services can operate independently. ZeroMQ is chosen but not the only technical choice as the low-level communication middleware because of its high performance and convenient communication model while using Google Protobuf as a marshaling library to unify the pattern of message contents. The partitioning of the JUNO detector into smaller subdetectors and segments ensures that these subsystems can either be readout together or independently. All running data except the raw physics events will be transmitted, processed, and recorded to the database. High availability (HA) mechanisms are foreseen to reduce single points of failure (SPOF) in the distribution system. This paper will introduce all the core services' functionality and techniques in detail.

The Jiangmen Underground Neutrino Observatory (JUNO)

The Jiangmen Underground Neutrino Observatory (JUNO) is an experiment under construction in China with the primary goal of determining the neutrino mass hierarchy (MH) with reactor anti-neutrinos. The JUNO detector system consists of a central detector, an active veto system and a calibration system. The central detector is a 35 m diameter transparent acrylic sphere containing a 20 kton liquid scintillator neutrino target. A primary photo-detection system consisting of 18,000 large (20” diameter) dynode and micro-channel plate photomultipliers surrounds the central detector. A second interlaced photo-detection system is made of 25,600 small (3” diameter) photomultipliers working in the single photo-electron regime for the reactor anti-neutrino detection. The detector is designed to achieve an unprecedented energy resolution of 3% @1MeV and an absolute energy scale uncertainty better than 1%. A veto system, consisting of a water Cherenkov detector and a top tracker, is used help maximally remove cosmogenic backgrounds. Due to its unprecedented scale and precision, JUNO will be an exceptional multipurpose detector with a rich physics program in neutrino oscillation, geo-neutrinos, astrophysical neutrinos and the search for physics beyond the Standard Model (sterile neutrinos, dark matter, proton decay and others).

Study on the Fracture Properties of the PMMA Structure for the JUNO Central Detector

Polymethyl methacrylate (PMMA) is increasingly used in building structures nowadays. PMMA materials utilized in structures have different fracture property compared with those used in aircrafts or biomedical equipment. Single-edge-notch bending (SENB) tests were firstly carried out at various temperatures (−40°C, −20°C, 0°C, 20°C, and 40°C) to determine the KIC values of base PMMA materials and connected areas. The crack-resisting capacity of PMMA plate is subsequently studied. The fracture property of the PMMA joint for the Jiangmen Underground Neutrino Observatory (JUNO) central detector is investigated. The results show that base PMMA material has higher KIC values than connected area. The KIC of base PMMA material is lowest at 20°C and highest at −20°C, while that of connected area is lowest at 40°C and highest at −40°C. For the PMMA joint of the JUNO detector, the cracks perpendicular to the X axis are more disadvantageous than those perpendicular to the Z axis. The stress intensity factors (SIFs) at the crack front of the embedded crack decrease with the increase of embedded depth. Due to the presence of two parallel surface or embedded cracks, the SIFs at the crack front decrease.

Light absorption properties of the high quality linear alkylbenzene for the JUNO experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kton multi-purpose underground liquid scintillator detector designed to determine the neutrino mass hierarchy, and measure the neutrino oscillation parameters. The excellent energy resolution and the large fiducial volume anticipated for the JUNO detector offer exciting opportunities for addressing many important topics in neutrino and astro-particle physics. Linear alkylbenzene (LAB) will be used as the solvent for the liquid scintillation system in the central detector of JUNO. The light attenuation lengths of LAB should be comparable to the diameter of the JUNO detector, hence very good optical transparency is required. However, the presence of impurities in the LAB renders an intrinsic limit for the transparency. This work focuses on the study of the effects of organic impurities in the LAB, and their light absorption properties particularly in the wavelength region of 350–450 nm. We have prepared LAB samples and measured their light attenuation lengths. These samples were then analyzed by a gas chromatography–mass spectrometry (GC–MS), and the structure formulas of organic impurities were ascertained. These impurities’ light-absorption properties in the wavelength region of 350–450 nm were theoretically investigated with time-dependent density functional theory (TDDFT). The overall optical transparency of the LAB samples was studied, which would further help us in promoting the LAB preparation technique for the mass production thereof, thus improving the transparency of the high quality LAB samples in the near future.

E- discrimination at high energy in the JUNO detector

Cosmic Ray and neutrino oscillation physics can be studied by using atmospheric neutrinos. JUNO (Jiangmen Underground Neutrino Observatory) is a large liquid scintillator detector with low energy detection threshold and excellent energy resolution. The detector performances allow the atmospheric neutrino oscillation measurements. In this work, a discrimination algorithm for different reaction channels of neutrino-nucleon interactions in the JUNO liquid scintillator, in the GeV/sub-GeV energy region, is presented. The atmospheric neutrino flux is taken as reference, considering $\mathop {{v_\mu }}\limits^{( - )} $ and $\mathop {{v_e}}\limits^{( - )} $. The different temporal behaviour of the classes of events have been exploited to build a timeprofile-based discrimination algorithm. The results show a good selection power for $\mathop {{v_e}}\limits^{( - )} $ CC events, while the $\mathop {{v_\mu }}\limits^{( - )} $ CC component suffers of an important contamination from NC events at low energy, which is under study. Preliminary results are presented.

Shielding the Earth Magnetic Field using Spherical Coils

The Jiangmen Underground Neutrino Observatory (JUNO) is a neutrino experiment consisting of 2 systems; central detector (CD) and veto systems. The CD is composed of thousands of photomultiplier tubes (PMTs) used to detect light signals from neutrino induced interactions with liquid scintillator inside the CD. Another set of PMTs is used as water Cherenkov detector, together with muon top tracker forming the veto system for background rejection [1]. However, the PMTs’ efficiency decreases when they are used in magnetic field. At JUNO’s construction site, the Earth Magnetic Field (EMF) is approximately 0.45 G [2]. Therefore, the PMTs of JUNO detector are necessary to be shielded from the EMF.This work aims to design current-carrying coils that generate magnetic field in the opposite direction to the EMF, thus, the two fields tend to cancel each other. We found that the magnetic field generated by the 32 circular coils forming a sphere of diameter 43.5 m can reduce the residual magnetic field to be lower than 10% of the EMF at the CD region and less than 20% at the veto region. Moreover, considering the secular change of the EMF’s inclination angle of approximately 2.87° over the 20 years of its operation, the coils can maintain the residual magnetic field both in the CD and the veto regions to be less than 10% and 20%, respectively.

Neutrino Physics and Astrophysics with the JUNO Detector

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kton liquid scintillator multi-purpose underground detector, under construction near the Chinese city of Jiangmen, with data collection expected to start in 2021. The main goal of the experiment is the neutrino mass hierarchy determination, with more than three sigma significance, and the high-precision neutrino oscillation parameter measurements, detecting electron anti-neutrinos emitted from two nearby (baseline of about 53 km) nuclear power plants. Besides, the unprecedented liquid scintillator-type detector performance in target mass, energy resolution, energy calibration precision, and low-energy threshold features a rich physics program for the detection of low-energy astrophysical neutrinos, such as galactic core-collapse supernova neutrinos, solar neutrinos, and geo-neutrinos.