Energy scale non-linearity and event reconstruction for the neutrino mass ordering measurement of the JUNO experiment

The JUNO experiment is a next-generation neutrino experiment under construction in vicinity of the Pearl River Delta in Southern China. It is expected to start data-taking in 2022 and aims to address the determination of the Neutrino Mass Ordering with 3-4 $\sigma$ sensitivity in about 6 years as its main goal. For that, it will measure the oscillated energy spectrum of electron anti-neutrinos from two nuclear power plants at a baseline of about 53 km with a required energy resolution of 3 % at 1 MeV and a sub-percent uncertainty on the energy scale. In order to reach these requirements, the JUNO detector consists of a large 20 kton liquid scintillator detector, which is instrumented with a dense PMT array consisting of about 18,000 large 20''-PMT's and 25,000 small 3''-PMT's. Besides this main goal it aims to address a large variety of important topics in neutrino and astroparticle physics.The first part of this thesis gives an overview over the current status of neutrino physics and shows why the determination of the Neutrino Mass Ordering is a key to explore a large area of physics topics. Moreover, it gives an overview of the JUNO experiment: the detector design and its calibration, the simulation framework, and the various physics goals of the JUNO experiment. Besides the detector design, a meticulous data analysis is needed to ensure, that the JUNO experiment can meet the requirements on the precision and accuracy on the reconstructed energy. Such analysis methods are presented in the second part of this thesis. Here, a model is presented, which can be used to describe the non-linear light response of positrons in the liquid scintillator. Based on the non-linearity model of electrons, an algorithm is introduced to calculate the more complex non-linearity model of gammas and combine both eventually to the non-linearity model of positrons. As the amount of detected light for a constant energy varies with the position of the energy deposition in the detector, the energy resolution of JUNO is impacted by the uncertainty of the reconstructed light emission vertex. The vertex reconstruction finds the light emission vertex by minimizing a likelihood function, which contains the information on the times and charges of the PMT hits. It is shown, that the uncertainty on the reconstructed vertex is especially small at the outer parts of the volume, where the effect on the energy resolution is the largest. Additionally to the improvement of the energy resolution, it is shown how the vertex reconstruction can be used to reconstruct the direction of an electron anti-neutrino flux from a point-source. Another important effect, which leads to biases on the reconstructed energy on JUNO is the pile-up of signal events with $^{14}$C decays.The organic scintillator contains large amounts of natural, radioactive $^{14}$C. These $^{14}$C decays are able to timely coincide with measured signal events to cause a smearing of the measured energy spectrum. To reduce the impact of these $^{14}$C decays, two analysis methods are presented. A clusterization algorithm identifies different energy depositions in the PMT hit time distribution. This algorithm is optimized on the sensitivity of JUNO to determine the Neutrino Mass Ordering. For event coincidences, which can not be separated in time, the vertex reconstruction is used to perform a likelihood test to identify these

TAO Conceptual Design Report: A Precision Measurement of the Reactor Antineutrino Spectrum with Sub-percent Energy Resolution

The Taishan Antineutrino Observatory (TAO, also known as JUNO-TAO) is a satellite experiment of the Jiangmen Underground Neutrino Observatory (JUNO). A ton-level liquid scintillator detector will be placed at about 30 m from a core of the Taishan Nuclear Power Plant. The reactor antineutrino spectrum will be measured with sub-percent energy resolution, to provide a reference spectrum for future reactor neutrino experiments, and to provide a benchmark measurement to test nuclear databases. A spherical acrylic vessel containing 2.8 ton gadolinium-doped liquid scintillator will be viewed by 10 m^2 Silicon Photomultipliers (SiPMs) of >50% photon detection efficiency with almost full coverage. The photoelectron yield is about 4500 per MeV, an order higher than any existing large-scale liquid scintillator detectors. The detector operates at -50 degree C to lower the dark noise of SiPMs to an acceptable level. The detector will measure about 2000 reactor antineutrinos per day, and is designed to be well shielded from cosmogenic backgrounds and ambient radioactivities to have about 10% background-to-signal ratio. The experiment is expected to start operation in 2022

Feasibility and physics potential of detecting 8^8B solar neutrinos at JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) features a 20 kt multi-purpose underground liquid scintillator sphere as its main detector. Some of JUNO's features make it an excellent location for B solar neutrino measurements, such as its low-energy threshold, high energy resolution compared with water Cherenkov detectors, and much larger target mass compared with previous liquid scintillator detectors. In this paper, we present a comprehensive assessment of JUNO's potential for detecting B solar neutrinos via the neutrino-electron elastic scattering process. A reduced 2 MeV threshold for the recoil electron energy is found to be achievable, assuming that the intrinsic radioactive background U and Th in the liquid scintillator can be controlled to 10 g/g. With ten years of data acquisition, approximately 60,000 signal and 30,000 background events are expected. This large sample will enable an examination of the distortion of the recoil electron spectrum that is dominated by the neutrino flavor transformation in the dense solar matter, which will shed new light on the inconsistency between the measured electron spectra and the predictions of the standard three-flavor neutrino oscillation framework. If eV , JUNO can provide evidence of neutrino oscillation in the Earth at approximately the 3 (2 ) level by measuring the non-zero signal rate variation with respect to the solar zenith angle. Moreover, JUNO can simultaneously measure using B solar neutrinos to a precision of 20% or better, depending on the central value, and to sub-percent precision using reactor antineutrinos. A comparison of these two measurements from the same detector will help understand the current mild inconsistency between the value of reported by solar neutrino experiments and the KamLAND experiment

Diminishing benefits of urban living for children and adolescents’ growth and development

Optimal growth and development in childhood and adolescence is crucial for lifelong health and well-being1–6. Here we used data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, to report the height and body-mass index (BMI) of children and adolescents aged 5–19 years on the basis of rural and urban place of residence in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The exception was for boys in most countries in sub-Saharan Africa and in some countries in Oceania, south Asia and the region of central Asia, Middle East and north Africa. In these countries, successive cohorts of boys from rural places either did not gain height or possibly became shorter, and hence fell further behind their urban peers. The difference between the age-standardized mean BMI of children in urban and rural areas was <1.1 kg m–2 in the vast majority of countries. Within this small range, BMI increased slightly more in cities than in rural areas, except in south Asia, sub-Saharan Africa and some countries in central and eastern Europe. Our results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified