Muon tracking with the fastest light in the JUNO central detector

Background: The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment designed to measure the neutrino mass hierarchy using a central detector (CD), which contains 20 kton liquid scintillator (LS) surrounded by about 18,000 photomultiplier tubes (PMTs), located 700 m underground. Purpose: The rate of cosmic muons reaching the JUNO detector is about 3 Hz, and the muon-induced neutrons and isotopes are major backgrounds for the neutrino detection. Reconstruction of the muon trajectory in the detector is crucial for the study and rejection of those backgrounds. Methods: This paper will introduce the muon-tracking algorithm in the JUNO CD, with a least-squares method of PMTs' first-hit time (FHT). Correction of the FHT for each PMT was found to be important to reduce the reconstruction bias. Results: The spatial resolution and angular resolution are better than 3 cm and 0.4 degree, respectively, and the tracking efficiency is greater than 90% up to 16 m far from the detector center.