Upgrades to the Event Simulation and Reconstruction for the Fermi Large Area Telescope

TL;DR

This paper discusses upgrades to the event simulation and reconstruction for the Fermi Large Area Telescope, focusing on addressing unexpected on-orbit features like detector ghosts to improve data analysis accuracy.

Contribution

It introduces new methods and plans for enhancing simulation and reconstruction to handle on-orbit detector effects, especially ghosts, for better data quality.

Findings

Identification of ghost effects in on-orbit data

Development of strategies to discriminate background particles

Plans for improved reconstruction algorithms

Abstract

The pre-launch event simulation and reconstruction performed beyond our expectations for real data, essentially without modification, and made possible the immediate start of science analysis. But the on-orbit data exhibit unanticipated features that necessitate upgrades to both the simulation (essentially complete) and the reconstruction (ongoing). The major new effect encountered on orbit is the presence of "ghosts," that is, remnant detector response to particles passing through the detector before the particle that triggered the event. These ghosts appear primarily in the form of extra tracks and/or energy deposits. As part of this upgrade, we plan to enhance our ability to discriminate against background particles by introducing additional analysis during the reconstruction phase. We present a description of the effect of ghosts, and of the work needed to deal with them, done and planned, as well as some other ideas for improving the reconstruction.