JUNO Conceptual Design Report

The Jiangmen Underground Neutrino Observatory (JUNO) is proposed to determine the neutrino mass hierarchy using an underground liquid scintillator detector. It is located 53 km away from both Yangjiang and Taishan Nuclear Power Plants in Guangdong, China. The experimental hall, spanning more than 50 meters, is under a granite mountain of over 700 m overburden. Within six years of running, the detection of reactor antineutrinos can resolve the neutrino mass hierarchy at a confidence level of 3-4$\sigma$, and determine neutrino oscillation parameters $\sin^2\theta_{12}$, $\Delta m^2_{21}$, and $|\Delta m^2_{ee}|$ to an accuracy of better than 1%. The JUNO detector can be also used to study terrestrial and extra-terrestrial neutrinos and new physics beyond the Standard Model. The central detector contains 20,000 tons liquid scintillator with an acrylic sphere of 35 m in diameter. $\sim$17,000 508-mm diameter PMTs with high quantum efficiency provide $\sim$75% optical coverage. The current choice of the liquid scintillator is: linear alkyl benzene (LAB) as the solvent, plus PPO as the scintillation fluor and a wavelength-shifter (Bis-MSB). The number of detected photoelectrons per MeV is larger than 1,100 and the energy resolution is expected to be 3% at 1 MeV. The calibration system is designed to deploy multiple sources to cover the entire energy range of reactor antineutrinos, and to achieve a full-volume position coverage inside the detector. The veto system is used for muon detection, muon induced background study and reduction. It consists of a Water Cherenkov detector and a Top Tracker system. The readout system, the detector control system and the offline system insure efficient and stable data acquisition and processing.Comment: 328 pages, 211 figure

Software and hardware development for the next-generation liquid scintillator detectors JUNO and OSIRIS

Large liquid scintillator~(LS) detectors are acknowledged instruments in the field of neutrino physics. Based on various successful experiments, reporting the currently best limits on several parameters of neutrino flavor oscillations, a new generation of detectors with several tens of kilotons of LS are under consideration. The Jiangmen Underground Neutrino Observatory~(JUNO) is a 20 kiloton LS detector, that is fully funded and under construction in China. Its main goal is the determination of the neutrino mass ordering~(MO) through a precision measurement of the reactor electron anti-neutrino spectrum. The first part of this thesis discusses the underlying theory of neutrino flavor oscillations, the JUNO detector design and how neutrinos of various sources can be detected with this instrument. The focus is laid on a correlated background for the inverse beta decay~(IBD) measurement of reactor anti-neutrinos, which stems from cosmic muons. When they traverse the detector, the muons can create unstable radioisotopes, which decay after a short time in a (beta + n) channel. In order to identify and reject this background, it is paramount to know the track of the muon precisely. For this purpose, a novel muon reconstruction algorithm is developed and tested in this work. It is based on the geometric model of the intersection of the first-light front with the PMT array. The track parameters are optimized in a likelihood fit based on probability density functions produced with a detailed detector simulation. In addition, a simulation of the full readout electronics is performed to yield the best estimate of the performance on real data. Excluding the edge of the CD, the muon track's distance from the detector center DeltaD can be determined with an uncertainty of 5 cm and its direction with 0.3°. The impact on the detector's exposure by a muon veto based on this reconstruction was also studied. Compared to a perfect knowledge of each muon track, the developed method only creates an additional 4 % of loss in exposure. In the second part, a pre-detector for JUNO is investigated. OSIRIS is a standalone, 20 ton LS detector, that will be used to monitor the radiopurity of the cleaned LS before it is filled into JUNO.In the scope of this work, a detailed detector simulation based on C++11 and Geant4 is developed. It is then used to determine the sensitivity of the detector to its main physics goal: the identification of Bi-Po coincidences from the decay chains of U-238 and Th-232 in the LS. Furthermore, a calibration campaign for OSIRIS is studied. Under consideration of the available hardware, the decision is made to utilize an automated calibration unit~(ACU) from the Daya Bay collaboration. The energy range of 0.5 - 3 MeV will be calibrated by exposing the detector simultaneously to Cs-137, Zn-65, and Co-60 in a single capsule. With different vertical positions on a fixed radial distance r = 120 cm from the detector's center, its non-uniformity can be properly sampled. Timing calibration of the PMTs with an accuracy of~0.1 ns is realized with a 430 nm LED, that can be deployed along the same vertical axis

Muon reconstruction with a geometrical model in JUNO

The Jiangmen Neutrino Underground Observatory (JUNO) is a 20 kton liquid scintillator detector currently under construction near Kaiping in China. The physics program focuses on the determination of the neutrino mass hierarchy with reactor anti-neutrinos. For this purpose, JUNO is located 650 m underground with a distance of 53 km to two nuclear power plants. As a result, it is exposed to a muon flux that requires a precise muon reconstruction to make a veto of cosmogenic backgrounds viable. Established muon tracking algorithms use time residuals to a track hypothesis. We developed an alternative muon tracking algorithm that utilizes the geometrical shape of the fastest light. It models the full shape of the first, direct light produced along the muon track. From the intersection with the spherical PMT array, the track parameters are extracted with a likelihood fit. The algorithm finds a selection of PMTs based on their first hit times and charges. Subsequently, it fits on timing information only. On a sample of through-going muons with a full simulation of readout electronics, we report a spatial resolution of 20 cm of distance from the detector's center and an angular resolution of 1.6o over the whole detector. Additionally, a dead time estimation is performed to measure the impact of the muon veto. Including the step of waveform reconstruction on top of the track reconstruction, a loss in exposure of only 4% can be achieved compared to the case of a perfect tracking algorithm. When including only the PMT time resolution, but no further electronics simulation and waveform reconstruction, the exposure loss is only 1%

Reduction of the 14C background in the JUNO experiment

The Jiangmen Underground Neutrino Observatory (JUNO) will be a 20 kt liquid scintillator neutrino detector. Its main goal is the determination of the neutrino mass hierarchy from a precise measurement of the energy spectrum of anti-electron-neutrinos 53 km away from the emitting nuclear reactor cores. To precisely measure the oscillation pattern of the reactor spectrum an unpredecent energy resolution for this kind of detector of 3% at 1 MeV is needed. Pile-up events with background from radioactive decays such as those from 14C can spoil the reconstruction of the neutrino energy. In this talk methods for discriminating pile-up events are presented. These methods are in addition to a simple clusterization algorithm, the utilization of spherical harmonics and a Likelihood-test of the photon hit time informations