IMPORTANT: we should come up with this memo for collaboration use within the next month

This is now a list of the most important checks we have made. We need to review and complete it, assign names to each section, provide a list of plots we want to (re)make. We also need to provide final, critical view on the status and things we think we should complete.

Introduction

The main goal of the BT was to validate the MC simulation of the LAT, therefore comparing data and MC of basic quantities over the largest possible phase space. Derived, more complex quantities, such as CTB* variables, are harder to compare due to differences in the LAT and CU geometries.
Great attention was paid to generate systematics comparison plots over the phase space for most variables.
Discrepancies of O(0.1) were found since the very beginning of the analysis, mostly for the number of TKR hits and the CAL energy scale.
Many cross-checks and updates on the geometry, simulation package, digitization algorithms, hardware calibrations were performed, and the status of discrepancies was monitored after each change.
In this note we want to document all this activity, state the current status of analysis, list open issues and lessons learned, draw our conclusions on the LAT MC fidelity and on the potential impact of MC imperfections on the LAT analysis strategy.

Simulation

Geant4 package and simulations checks

• G3-G4 comparisons
• G4-EGSE comparisons
• CU geometry handling: standalone G4 CUTower simulation
• Low energy EM physics and discovery of LPM effect - improvement in TKR hits
• Hadronic physics lists
• Realistics TKR signal digitization algorithm

Geometry cross-checks

• TKR material audit
  • w thickness - corrected in BT and GR
  • missing mass in the tray boundaries and in the bottom tray - not corrected
• CAL material audit - implemented
• Realistic TKR tray geometry (honeycomb core, glue dots, strips)
• Effect of TKR alignment

Data integrity checks

Beamline checks and scan on extra material

• beam spot tuning and effect on data-MC agreement
• pressure scan on cerenkov, studies with extra layers of material before the CU and between TKR and CAL

CAL calibration

• pedestal drift from rate effect
• pedestal variations and correction with temperature
• light yeld correction with temperature
• LAC thresholds measurement and update in the simulation
• Cross-talks: FLE-FHE, inter-layer and effects on small-big diode intercalibration

TKR response

• no effects seen for high rates
• GTRC/FIFO registers settings
• Optimised split readout

Results

• data-MC agreement matrix
• projections of current discrepancies on background rejection

Tools and lessons learned (for internal collaboration use)

This should be a list of useful things we have developed which could help in minimizing the effort for a continuing analysis and a list of things to improve or avoid

• BtSystemTest
• use of pipeline II - how much effort?
• bad documentation of merit and svac tuples
• confusing naming for tkr hits variables (took a long time to realize that hits variables in merit are actually clusters variables and real hits in the svac)