The Data Acquisition (DAQ) system of LHCb is a complex, real-time system connecting more than 300 readout boards with more than 1500 servers by means of high-performance network 68 switches. The ...total data rate through this network is more than 60 GB/s. The DAQ network has a FAT-tree topology, composed of an aggregation and a distribution layer, where traffic flows unidirectionally to the server farm. This system will be upgraded to provide LHCb with an all-software, trigger-free readout starting from 2020. Consequently more CPU power in the from of servers are needed and the DAQ network will grow to a capacity of 40 Tbps. A PC-based readout system would receive data incoming from the detector, which would then be scattered across builder nodes, and further distributed to a computing farm for data filtering. The design bandwidth of such a DAQ system requires rates as high as 400 Gbps single-duplex per node. These builder nodes will be connected with inexpensive, high-bandwidth data-centre switches in order to minimize the system cost. The behaviour of such a event-building network can of course be studied in simulation but experience tells us that it is imperative to test, in particular to find out limitiations in the switches themselves and to which extent various event-building protocols can mitigate these limitations. We present a protocol, topology and transport independent emulation software DAQPIPE. It allows us to test different communication architectures, such as push or pull, with regards to the initiator of the communication. Different topologies and transport protocols can also be tested. We also present throughput and stress tests on an Infiniband FDR multi-rail based LAN network setup, with a focus on the network performance.
Long-lived particles (LLPs) are highly motivated signals of physics Beyond the Standard Model (BSM) with great discovery potential and unique experimental challenges. The LLP search programme made ...great advances during Run 2 of the Large Hadron Collider (LHC), but many important regions of signal space remain unexplored. Dedicated triggers are crucial to improve the potential of LLP searches, and their development and expansion is necessary for the full exploitation of the new data. The public discussion of triggers has therefore been a relevant theme in the recent LLP literature, in the meetings of the LLP@LHC Community workshop and in the respective experiments. This paper documents the ideas collected during talks and discussions at these Workshops, benefiting as well from the ideas under development by the trigger community within the experimental collaborations. We summarise the theoretical motivations of various LLP scenarios leading to highly elusive signals, reviewing concrete ideas for triggers that could greatly extend the reach of the LHC experiments. We thus expect this document to encourage further thinking for both the phenomenological and experimental communities, as a stepping stone to further develop the LLP@LHC physics programme.
