Authors:	Depnering, Wilfried Walter
Title:	Scintillation Light Transport In The Large Reactor Antineutrino Detector JUNO
Online publication date:	28-May-2021
Year of first publication:	2021
Language:	english
Abstract:	In low-energy neutrino physics, liquid scintillator (LS) detectors play a major role. The Jiangmen Underground Neutrino Observatory (JUNO) will be a multipurpose neutrino experiment and is currently under construction in South China. JUNO's main goal is the determination of the neutrino mass ordering at a 3-4σ significance within an operation time of six years. With a target mass of 20 kt, JUNO will be the largest LS detector constructed so far. A crucial requirement is to reach an energy resolution of at least 3% @ 1 MeV. Besides other aspects, this demands a sufficiently high transparency of the liquid scintillator. This transparency is expressed in terms of the attenuation length L and scattering length Ls. In order to fulfill the demands on the energy resolution, JUNO strives for values of L=20 m and Ls =27 m, respectively. To ensure that the detector performance meets these requirements for the whole operation period and does not degrade over time, the target's transparency will be continuously monitored. This is the purpose of the laser calibration system AURORA (A Unit for Researching On-line the LS tRAnsparency), which is installed in the water volume surrounding the JUNO central detector. The first part of this thesis is about the design, construction, and performance tests of AURORA. A specially selected diode provides laser light at a wavelength of λ=430 nm, which corresponds to the spectral region of the scintillator light emission. The light is distributed into an array of 100 m long fibers by an automated fiber switch. The laser light is decoupled from GRIN lenses that permit to collimate the beam underwater. Full aperture angles of less than 0.25° can be achieved. To avoid any damage to the PMTs, piezoelectric actuators have been introduced to ensure that the beams can be remotely tilted by around 1°. Thus, even if the geometry shifted due to the detector filling, it would be possible to compensate for misalignment. Any interference with the electronic readout of the PMTs has to be avoided. The generated magnetic field of these electro-mechanical devices has been tested and found to be acceptably small. The second part of this thesis focuses on the investigation of AURORA's potential to determine the attenuation length L and the scattering length Ls of the LS studying statistical and systematical uncertainties. To evaluate the feasibility and sensitivity of the developed analysis approach, detailed studies with JUNO's official simulation framework offline have been conducted. It is found that a 50 s run provides sufficient statistics to reduce the relative uncertainty to the 0.1% level. Moreover, several sources of systematic uncertainties were studied. For an absolute measurement of the attenuation and scattering length, systematic uncertainties of ΔL=±13 cm and ΔLs=±23 cm can be achieved. For a relative measurement that compares the development of the LS transparency over time, several systematic contributions do not have to be included. In this case, the systematic uncertainties are reduced to ΔL=±7 cm and ΔLs=±11 cm, respectively.
DDC:	530 Physik 530 Physics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 08 Physik, Mathematik u. Informatik
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-5976
URN:	urn:nbn:de:hebis:77-openscience-d2941e3b-6f0d-4630-828e-fbf92891708d4
Version:	Original work
Publication type:	Dissertation
License:	CC BY
Information on rights of use:	https://creativecommons.org/licenses/by/4.0/
Extent:	xvi, 227 Seiten, Illustrationen, Diagramme, Karte
Appears in collections:	JGU-Publikationen