Performance of the ATLAS Muon Trigger and Phase-1 Upgrade of Level-1 Endcap Muon Trigger

The ATLAS experiment utilises a trigger system to efficiently record interesting events. It consists of first-level and high-level triggers. The first-level trigger is implemented with custom-built hardware to reduce the event rate from 40 MHz to100 kHz. Then the software-based high-level triggers refine the trigger decisions reducing the output rate down to 1 kHz. Events with muons in the final state are an important signature for many physics topics at the LHC. An efficient trigger on muons and a detailed understanding of its performance are required. Trigger efficiencies are, for example, obtained from the muon decay of Z boson, with a Tag&Probe method, using proton-proton collision data collected in 2016 at a centre-of-mass energy of 13 TeV. The LHC is expected to increase its instantaneous luminosity to $3\times10^{34} \rm{cm^{-2}s^{-1}}$ after the phase-1 upgrade between 2018-2020. The upgrade of the ATLAS trigger system is mandatory to cope with this high-luminosity. In the phase-1 upgrade, new detector called New-Small-Wheel (NSW) will be introduced at the inner station region. Finer track information from the NSW can be used for the muon trigger logic to enhance the performance significantly. In order to handle data from both TGC and NSW, some new electronics have been developed, including the trigger processor board, Sector Logic. The Sector Logic has the latest FPGA mounted, to make use of the Multi-Gigabit transceiver techniques, which will be used to receive NSW information. The readout system for the trigger data has also been re-designed, in which data transmission is planned to be implemented by TCP/IP, instead of by a special ASIC. The poster will outline the performance of the muon trigger in 2016 and the planned upgrades of the first-level endcap-muon trigger system. Particular emphasis will be placed on the electronics and its firmware. The performance of the software readout system, and the latest results of the trigger performance study will also be discussed.