Study of timing differences between Super Cells in ATLAS Liquid Argon Calorimeter for the feasibility of using summed signals for the Digital Trigger.

The current Digital Trigger for Liquid Argon performs worse than the Legacy Trigger for low energy interac- tion, this is a problem for Ultra Peripheral Heavy Ion collisions. The Phase I upgrade improved granularity by dividing up Trigger Towers into Super Cells allowing for more information about the shower to recorded. This change also required the Trigger calculations to change from analogue to digital, to process more com- plex algorithms. These improvements have created challenges for lower energy particles as this improved granularity has divided up the signals amplitude to the same order of magnitude as noise. Therefore, low energy showers in the detector have failed noise cuts and not been passed onto the later levels of the Trigger, when they would have been in the Legacy Trigger. One potential solution, is to sum the digital signals from the Super Cells into a structure similar to a Legacy Trigger Tower, this would create larger signals passing the noise cuts. For this to be possible, the timings of different Super Cells need to be aligned to create a summed peak. The real time of each Super Cell is different due to the electronics. However, the calculated τ time from the Optimal Filtering Coefficients has shown to be closely aligned from Pulseall data. The Super Cells are most closely aligned within their layer with averaged standard deviations of 0.1 ns and have a average standard deviation of 0.5 ns within Trigger Towers. This has shown positive feasibility of Super Cells being closely aligned to be able to be summed within a structure of a layer or a Trigger Tower. However, the improvement for Heavy Ion collisions is not clear as the summed samples require special Optimal Filtering Coefficients which have not been calculated yet. With these coefficients a full investigation into whether this technique would improve the Trigger to the same level of the Legacy Trigger could be concluded.