Muon reconstruction with a geometrical model in JUNO

Abstract

A: The Jiangmen Neutrino Underground Observatory (JUNO) is a 20 kton liquid scintillator detector currently under construction near Kaiping in China. The physics program focuses on the determination of the neutrino mass hierarchy with reactor anti-neutrinos. For this purpose, JUNO is located 650 m underground with a distance of 53 km to two nuclear power plants. As a result, it is exposed to a muon flux that requires a precise muon reconstruction to make a veto of cosmogenic backgrounds viable. Established muon tracking algorithms use time residuals to a track hypothesis. We developed an alternative muon tracking algorithm that utilizes the geometrical shape of the fastest light. It models the full shape of the first, direct light produced along the muon track. From the intersection with the spherical PMT array, the track parameters are extracted with a likelihood fit. The algorithm finds a selection of PMTs based on their first hit times and charges. Subsequently, it fits on timing information only. On a sample of through-going muons with a full simulation of readout electronics, we report a spatial resolution of 20 cm of distance from the detector's center and an angular resolution of 1.6 • over the whole detector. Additionally, a dead time estimation is performed to measure the impact of the muon veto. Including the step of waveform reconstruction on top of the track reconstruction, a loss in exposure of only 4% can be achieved compared to the case of a perfect tracking algorithm. When including only the PMT time resolution, but no further electronics simulation and waveform reconstruction, the exposure loss is only 1%. K: Particle tracking detectors, Neutrino detectors, Cherenkov detectors, Large detector systems for particle and astroparticle physics 1Corresponding author.

Muon reconstruction with a convolutional neural network in the JUNO detector

“…When the muon track is close to the edge of CD, the position of the incident point and the exit point are very close to each other which makes an accurate reconstruction of the track direction difficult. This degradation of angular reconstruction at large distances from the CD center is also seen with the existing muon reconstruction methods [2,3]. Overall, the angular resolution is better than 0.6 degrees and the spatial resolution is better than 10 cm.…”

“…-Muon reconstruction with a geometrical model [2] which is based on the geometrical shape of the first light and provides a spatial resolution of 20 cm and an angular resolution of 1.6 degree over the whole detector. -Muon tracking with the fastest light [3] which uses the least squares fit to the PMT first hit time (FHT) measurements.…”

Topological track reconstruction in unsegmented, large-volume liquid scintillator detectors

“…The lateral resolution for the start point of the muons and the relative energy resolution were found to be 2-5 cm and ∼ 1%, respectively. A muon reconstruction for the spherical 20 kt LS detector JUNO tested with events from a a detailed MC simulation achieves a mean deviation between true and reconstructed angle of about 1.6 • over the entire detector [28]. For the resolution of the minimum track distance to the detector center, essentially describing the lateral resolution, a value of 20 cm is reported.…”

“…The only assumption made for the topological reconstruction is that a reference point on the topology is known reasonably well in space and time (the time of the energy deposition) and that the particle going through this point moves on a straight line with speed c 0 . For example, the reference point could be provided by an external muon tracking system or by other reconstruction methods based on timing information, like the "backtracking-algorithm" [26], or geometrical models [27,28].…”

Status of the Jiangmen Underground Neutrino Observatory

“…From [2] Section IBD Geo-s Accidental 9 172 ms, respectively, 99% of the 9 Li and 8 He isotopes produce IBD-like signatures at a 3 m distance to the muon track [3,4]. Therefore, the strategy for the muon veto includes a partial volume veto of the area of the liquid scintillator contained in a cylinder with a radius of 3 m around the muon track for a time of 1.2 s [5]. Other considerable background sources are the following:…”