Analysis of Light Attenuation Length Measurement of a High Quality Linear Alkylbenzene for the JUNO Experiment

Abstract

Jiangmen Underground Neutrino Observatory (JUNO) is the next generation neutrino experiment which aims at neutrino mass hierarchy problem along with many other cutting-edge studies concerning neutrinos. Located 700m underground in Jiangmen China, JUNO's central detector is an acrylic sphere filled with 20kt liquid scintillator with linear alkylbenzene(LAB) as scintillator solvent. To ensure that an unprecedented energy resolution of $\sigma_E/E \leqslant 3\%$ can be reached, LAB used in JUNO must have excellent transparency at the wavelength ranging from 350nm to 450nm. In the past decade much effort has been devoted to the development of high transparency LAB based on the measurement of light attenuation length. Through a close cooperation with Jingling Petrochemical Corporation in Nanjing, transparency of LAB samples prepared for JUNO has been improved progressively. However, this improvement is also pushing our apparatus towards approaching its measuring limit, undermining the credibility of our measurement. In order to get a result accurate and precise, an apparatus upgrading and a more detailed error analysis is inevitable. In this article, we present an analysis of how apparatus upgrading helps with decreasing measuring errors, and we conducted measurements using the new apparatus on several samples. A detailed error analysis is followed to validate the results. We propose to apply statistical methods featuring Monte Carlo simulation to estimate systematic uncertainties. Deviations caused by fit models is also considered and the overall uncertainty is obtained by combining two independent measurements. We finally report the light attenuation length of a newly improved LAB sample to be $29.90\pm 0.95$m, which gives a new high of all the preceding samples we tested. This study may provide a strong evidence of JUNO's feasibility to reach its energy resolution.