Realistic Detector Geometry Modeling and Its Impact on Event Reconstruction in JUNO

TL;DR

This paper models the realistic detector geometry of JUNO, showing that accurate geometry is crucial for precise event vertex reconstruction, while energy resolution remains unaffected.

Contribution

It introduces a method to predict PMT positions from limited survey data and demonstrates the importance of realistic geometry in event reconstruction accuracy.

Findings

Realistic geometry prediction reduces vertex bias to below 40 mm.

Detector deformation has negligible impact on energy resolution.

Incorporating realistic geometry stabilizes reconstruction algorithms.

Abstract

JUNO is designed to determine the neutrino mass ordering with an energy resolution of 3% at 1 MeV. In the real detector, however, deformations of the central stainless-steel structure during installation lead to deviations of the photomultiplier tube (PMT) positions from their design values. Based on the limited survey data of the PMTs and the stainless-steel truss, we perform a correlation analysis of the measured points and propose a method to predict the positions of all PMTs. Using the resulting realistic geometry, we demonstrate that the detector deformation has a negligible effect on the energy reconstruction. In contrast, inaccuracies in the assumed geometry can introduce vertex biases of up to 40 mm. Incorporating the realistic geometry into the calibration-based PMT response model removes this bias and preserves the stability of the reconstruction algorithms.