Data Flow in the Mu3e DAQ

The Mu3e experiment at the Paul Scherrer Institute (PSI) searches for the charged lepton flavor violating decay
$\mu ^{+} \rightarrow e^{+} e^{+} e^{-}$
. The experiment aims for an ultimate sensitivity of one in
$10^{16} \mu $
decays. The first phase of the experiment, currently under construction, will reach a branching ratio sensitivity of
$2\cdot 10^{-15}$
by observing
$10^{8} \mu $
decays per second over a year of data taking. The highly granular detector based on thin high-voltage monolithic active pixel sensors (HV-MAPS) and scintillating timing detectors will produce about 100 Gbit/s of data at these particle rates. The field-programmable gate array (FPGA)-based Mu3e data acquisition (DAQ) system will read out the different detector parts. The trigger-less readout system is used to sort, time align, and analyze the data while running. A farm of personal computers (PCs) equipped with powerful graphics processing units (GPUs) will perform event reconstruction and data reduction. This article presents the ongoing integration of the subdetectors into the DAQ system, especially focusing on the time aligning and the data flow inside the FPGAs of the filter farm. It discusses the DAQ system used in the Mu3e Integration Runs performed in spring 2021 and 2022, while providing results of the synchronization of the different detectors.