  The Jiangmen Underground Neutrino Observatory (JUNO), 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 to 450 nm. we have prepared LAB samples and
measured their light attenuation lengths. These samples were then analyzed by a
gas chromatography mass spectrometry, and the structure formulas of organic
impurities were ascertained. These impurities' light absorption properties in
the wavelength region of 350 to 550 nm were theoretically investigated with PCM
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.
